One of my clients is a very good runner. Good enough to qualify for Boston. At his peak, he was running five days a week, sometimes six. He’s also had recurring bone-stress problems that have forced him to stop running for extended periods.

I’m not his running coach.

I handle his mobility, strength, and conditioning. Someone else programs his running.

I’m not saying that running five days per week caused his injuries. Bone stress injuries are multifactorial. But I am asking whether frequency belongs in the discussion.

His situation has made me think harder about a question that sounds simpler than it actually is: how often do we really need to run?

I’ve been asking that same question about myself. I’m currently preparing for a Spartan Trifecta, three races in one weekend, with two ACL-deficient knees and chronic lateral knee issues that tend to get worse when I run more often. I’m running twice a week at the moment: one shorter interval session on the treadmill, one longer trail run.

That’s not because two runs a week is optimal. I have no idea if it’s optimal. For me, the question is how much running I need to develop the specific abilities I’ll need on race weekend. Because running does two things at once: it trains your cardiovascular system and mechanically loads your body. That distinction matters.

The research isn’t as clear as you might expect

Faster runners generally accumulate more mileage and run more frequently. A recent observational study of 917 Boston Marathon runners found that weekly running frequency was associated with marathon performance, along with total distance and quality sessions.

That doesn’t prove frequency caused the performance. Nobody randomly assigned identical runners to three versus five running days while holding mileage, intensity, and training history constant. That’s the experiment we’d really want and, as far as I can tell, nobody has done that.

Interestingly, the same study found that runners who reduced their weekly run frequency relative to an earlier training block performed better than those who maintained or increased it. That result is also observational, and may reflect successful tapering rather than a general case for fewer runs, but it’s a reminder that more frequent running isn’t necessarily what drives better performance.

So the most defensible conclusion isn’t that more frequent running is better, or that less frequent running is better. It’s that running frequency in isolation is something we understand less well than you’d expect. That leads to a more useful question: not how many days should I run, but what am I trying to accomplish with each run?

A run starts several clocks

Finish a run and we tend to talk about “recovery” as though your entire body entered one process.

It didn’t.

Your cardiovascular system experienced one kind of stress. Your muscles experienced another. Your tendons, bones, joints, and nervous system each had their own loading, and none of them define recovery in quite the same way.

We don't have evidence good enough to build a universal table that says exactly how long each one takes after any given run, across every athlete and every tissue. What we do know is that these systems don't move in lockstep. There isn't one recovery clock. There are several, and the one you feel first isn't always the one that matters most. Sore muscles are obvious. Bone and tendon less so.

Bone gives us a fascinating example

Every time your foot strikes the ground, your skeleton experiences mechanical strain. Cells within bone sense that strain and coordinate the response to loading. But bone’s response doesn’t keep increasing at the same rate as you pile up more repetitions. In a foundational animal experiment, bone became less sensitive to repeated loading over the course of a session, and when the same total stimulus was broken into separate bouts with recovery between them, bone formation increased compared with loading delivered continuously.

Those experiments were performed in rats. They don’t prove humans should run every other day. But the underlying biology has shaped thinking around bone-stress injuries, and a recent scoping review of return to running after tibial bone stress injury notes a mechanistic rationale for initially spacing running exposures, while emphasizing individualized, graduated progression.

I’m not going to tell a healthy runner that bone biology dictates a mandatory recovery interval. I take something more modest from it: more mechanical loading doesn’t necessarily produce proportionally more adaptation. The mechanical cost keeps accumulating even though the adaptive response begins to level off. Bone-stress injuries are thought to develop when repeated loading exceeds the bone’s capacity to adapt and repair over time, a process influenced by much more than training alone.

Tendons are running their own experiment

Tendons complicate the picture too. Human research shows tendon collagen metabolism responds to loading, but that response depends on the tendon, the exercise, and whether the tissue is healthy or already symptomatic. Animal work shows Achilles tendon mechanical properties change across hours, days, and weeks of repeated exercise, but translating that into “wait 48 hours before running again” goes well beyond the evidence. The takeaway isn’t a specific waiting period. It’s that tendon recovery doesn’t map neatly onto a training calendar either.

Age doesn’t give you the answer

I expected the research to hand me a simple answer: older athletes recover more slowly, so they should run less frequently.

It didn’t.

Masters athletes retain remarkable endurance capacity, and running economy can stay comparatively well preserved in well-trained masters runners even as other determinants of performance decline with age. Some evidence suggests that recovery from prolonged or eccentric-heavy exercise can differ with age, particularly at the neuromuscular level, but that’s a long way from saying every 55-year-old needs another day between runs.

Age by itself isn’t enough to prescribe frequency. What matters more is what you’re asking your body to recover from. A flat 30-minute easy run isn’t the same exposure as two hours on trails, and a healthy lifelong runner isn’t dealing with the same constraints as someone returning from a stress fracture.

That’s a better question than how old you are: what tissue or system is currently limiting how much running you can tolerate?

Here’s where cross-training gets interesting

Suppose you want four cardiovascular sessions this week. Why do all four have to be runs?

A 2026 systematic review and meta-analysis of randomized trials comparing running-only training with cycling-only or combined running-and-cycling approaches found no clear between-group difference in treadmill VO₂max or running performance across seven studies.

That doesn’t mean cycling and running are interchangeable. The studies were few, short, and heterogeneous, and the confidence intervals were wide enough that the authors explicitly cautioned against concluding equivalence. But the finding still points somewhere useful: some cardiovascular adaptations transfer across modalities.

That creates options.

That’s what I’m testing on myself

I’m running twice a week, but I’m not only conditioning twice a week. A SkiErg gives me a serious high-intensity aerobic stimulus without adding thousands more foot strikes.

What it can’t give me matters just as much: it doesn’t rehearse descending a rocky trail, condition my feet and lower legs to repeated impact, or practice the stiffness and coordination involved in economical running. It certainly doesn’t prepare my knees for hours of uneven terrain. That’s why the long trail run stays.

That’s the experiment: which adaptations require running, and which ones can I get somewhere else at a lower orthopedic cost?

Every run should serve a purpose

Before adding another run, ask what you’re buying with it. A long trail run buys terrain exposure, downhill tolerance, time on your feet, and race-specific durability. Hard to replace. A shorter quality run buys practice at race-relevant speeds and a chance to build the coordination and economy that come with faster running. Also useful.

But if the answer is simply “I need more cardio,” you have options: cycling, deep-water running, rowing, SkiErg. Deep-water running appears capable of producing cardiorespiratory improvements broadly comparable to land-based training while substantially reducing weight-bearing load. Not better than running. Just a different tool.

Resistance training belongs in this conversation too. It’s a weak driver of aerobic capacity, so it’s not standing in for a missed run the way cycling or rowing can. What it does instead is change what your running needs to accomplish. Systematic reviews and meta-analyses of controlled trials in middle- and long-distance runners suggest that heavy resistance training, plyometric training, and combined strength methods can improve running economy, the amount of oxygen a given pace costs you. That’s not replacing the running stimulus. It’s building the qualities that support the running you’re still doing.

So how often should you run?

I don’t know, and based on the literature I’ve spent far too much time reading, nobody else knows your number either.

Running frequency itself isn’t consistently associated with running-related injury. Reviews find conflicting evidence across frequency, volume, duration, and intensity, while previous injury remains the more consistent signal. Newer work suggests large jumps in the distance of a single run may matter more: in a prospective study of more than 5,000 runners, a run that exceeded the athlete’s longest run from the prior 30 days by more than 10% was associated with a higher overuse-injury rate. That matters because cutting run days while trying to preserve weekly mileage can turn one or two runs into their own kind of load spike.

This isn’t an argument that fewer runs are automatically safer. Sessions get longer, you lose reps at practicing running, and if you’re training for a marathon, swapping too much running for a bike eventually collides with specificity.

The objective isn’t to minimize running. It’s to justify it.

Ask three questions:

• What adaptation am I trying to produce?

• Does that adaptation require running?

• What is currently limiting my ability to tolerate another running exposure?

Your answers might say six days this week, or three. I’m betting on two, and I won’t know if that was enough until I race.

The goal isn’t to run as little as possible. It’s to reserve running for the adaptations that actually require it.

Running is an expensive way to buy some adaptations. It’s the only way to buy others. Know which one you’re paying for. Your heart can get a powerful aerobic stimulus from running or pulling on a SkiErg.

Your knees know which one you chose.

For the first two weeks of this Spartan experiment, I’ve been trying to protect my knees from the very things they’ll eventually need to handle. That was intentional. But ten weeks out, I can’t keep dancing around the demands of the race.

If you’ve read my previous articles, you know that both of my ACLs are torn and I have degenerative changes in both knees. They’re a constant reminder that I don’t have much margin for careless training.

So when I started preparing for a Trifecta twelve weeks out, I didn’t begin by running trails. I kept the running volume low and all of it on a treadmill. Much of my lower-body strength work has been concentric dominant, and I’ve used the sled heavily.

The idea was to build fitness without immediately piling on eccentric loading, impact, and torque that my knees already struggle to tolerate. I still think that was the right decision.

But Spartan isn’t contested on a treadmill.

Protection and preparation aren’t the same thing

Spartan racing isn’t particularly friendly to knees. The terrain is uneven. There are climbs and descents. Foot placement isn’t always predictable, and obstacles interrupt your running rhythm.

Fatigue makes all of those things worse.

I can improve my cardiovascular fitness on a treadmill. I can develop lower-body strength and power with exercises that don’t irritate my knees very much. Those are smart choices, but none of them prepares my knees to absorb a bad step on a technical descent.

That’s the uncomfortable part of training around an old injury: eventually, you have to train the thing you’ve been protecting. The question is how much.

I’ve gotten that wrong before.

A couple of years ago, while training for a 50K, I gradually increased my running distance and frequency. At first, the knees would complain and then settle. Eventually they stopped settling altogether.

Mild discomfort became persistent pain, and by the end of that training cycle, I was hobbling around.

There wasn’t one workout I can point to and say, That’s the one that did it. It was the accumulation.

That experience has influenced this Spartan build more than anything I’ve read about how many miles I should be running ten weeks before a Beast.

I don’t want to find out how much running I can survive. I want to find out how much running I can repeatedly recover from.

The first trail test

Sunday was my first trail run in three months and only my fourth this year. I chose a roughly three-mile loop I know well. It starts with a steep climb.

My heart rate climbed quickly, but my knees were reasonably quiet. As I kept running, the left became a little more noticeable. Then I misstepped. A sharp pain shot through the right knee.

That’s exactly the kind of thing I’ve been worried about.

I adjusted my gait and kept moving, and the pain settled. A few hours after I finished, both knees felt about the same as they had before the run. That was the most useful piece of information I got from the run.

The trail stressed my knees. They reacted, and then they returned to baseline.

One run doesn’t tell me much about what will happen over the next ten weeks, but that’s the response I need if this is going to work.

I’m watching the reset

I’ve spent a lot of time considering how much knee pain I’m willing to tolerate during this experiment. I’m beginning to think the better question is what happens after the pain.

A misstep can produce a surprisingly sharp response. That gets my attention in the moment, but the intensity of an individual pain spike doesn’t necessarily tell me what happens next.

What worries me more is when the knee doesn’t return to where it started.

That’s what happened during the 50K build. A run would leave something behind, then I’d run again. Eventually the residual irritation from one session became the starting point for the next.

That’s the pattern I can’t allow to develop this time.

That principle applies to more than bad knees. If the stress from one training session is still affecting what you can do when the next one arrives, the problem is no longer the individual workout. It’s the accumulation.

So I’m tracking pain and performance before training, during training, immediately afterward, and the next morning. I’m less interested in whether every number is zero than I am in whether the baseline keeps resetting.

Two runs, two different jobs

I’ve been trying to keep my running volume to the minimum I think will prepare me for the races. I’m even more convinced that’s the right approach now.

Rather than adding more runs, I’m going to make the two I already have more specific.

The weekday run stays on the treadmill. That’s where I can deliberately manipulate pace, incline, interval duration, and eventually the spacing between obstacle-like efforts. As the training progresses, I can also break the running into intervals that better reflect the distance between obstacles in the different Spartan races.

Sunday has a different job.

I don’t need to manufacture specificity on the trail. Climbs, descents, uneven footing, changing pace, and bad steps are already built in.

And unlike 40 minutes of easy treadmill running, I actually look forward to doing it.

For now, I’m not particularly interested in adding a third run. My previous mistake wasn’t that I failed to run enough. It was that I eventually accumulated more running than my knees could recover from.

I don’t see a reason to repeat that mistake.

The risk has changed

At the beginning of this experiment, the obvious risk was doing too much too soon. That risk hasn’t disappeared, but another one is starting to matter: doing too little of the things the race actually requires.

I could spend the next ten weeks making my training increasingly knee-friendly. I could get stronger, improve my conditioning, and keep my symptoms relatively quiet.

And arrive in Dallas with knees that have barely seen a technical descent.

That doesn’t strike me as particularly good preparation either.

So the balance changes from here. I’m going to expose my knees to the demands I’ve been protecting them from, carefully.

Sunday was the first dose. My knees complained, and a few hours later they were back where they started.

Next week I’ll give them another one. If they keep resetting, I’ll gradually ask for more. If they stop resetting, the plan changes.

You may still be lifting, running, racing, or playing sports.

The problem is not that you stopped trying.

The problem is that recovery is less forgiving, old injuries carry more influence, and training decisions that once produced progress can now leave you managing the same recurring problems.

That does not mean you need to stop training hard.

It means you need a better system.

I’ve been training people since my mid-twenties. I’m 55 now, and I’m still lifting, running, and preparing for competition with two torn ACLs, osteoarthritis in both knees, and more than three decades of training history behind me.

The central idea behind Athlete for Life is simple:

Staying athletic long-term requires more than effort. It requires judgment.

That means knowing how to apply stress, how to respect recovery, how to build the capacities your sport demands, and how to adjust training to the body you have now without lowering your standards.

The articles below will give you the clearest introduction to that approach.

1. Begin with why the old playbook stops working

You Don’t Stop Being an Athlete After 40 →

Most training advice assumes that the same methods should keep working as long as you remain disciplined enough to follow them.

After 40, that assumption becomes less reliable.

The fundamentals do not disappear, but your margin for error changes. Recovery becomes less forgiving, joints carry more history, and small programming mistakes begin to accumulate instead of quietly resolving themselves.

This article introduces the central idea behind Athlete for Life:

Age does not require you to stop being an athlete. It requires your methods to evolve.

2. Understand the difference between fitness and durability

Fitness and Durability Are Not the Same Thing →

You can be strong, lean, conditioned, and highly motivated—and still be unable to tolerate the training required to express those qualities consistently.

Fitness describes what you can do.

Durability describes what your body can repeatedly withstand.

That distinction becomes increasingly important after 40, especially when old injuries, joint limitations, and slower recovery begin influencing what happens between workouts.

This article explains why durability must be trained deliberately rather than treated as a side effect of getting fit.

3. See the system applied to a real problem

How I’m Training for Spartan With Two Bad Knees →

Theory matters, but training decisions become clearer when there are real stakes and real constraints.

I am currently preparing for a Spartan Trifecta Weekend: three races over two days, including a Beast, Super, and Sprint.

I am also doing it with two torn ACLs, osteoarthritis in both knees, and a clear boundary: completing the challenge is not worth permanently worsening my knees.

This series documents how I am balancing strength, running, power, conditioning, joint capacity, recovery, and restraint.

It is not a story about ignoring pain or proving that age does not matter.

It is an experiment in how to keep pursuing meaningful physical goals when age and injury history demand better decisions.

4. Identify the weak link in your own training

Download the Train Hard After 40 Diagnostic Checklist →

If your body keeps breaking down in the same places, the painful area is not always the whole problem.

The issue may be a mismatch between your training load, joint capacity, movement options, recovery, conditioning, or program structure.

The Train Hard After 40 Diagnostic Checklist will help you examine the major parts of your training system and identify where the weak link may be.

It takes less than five minutes.

What you can expect from Athlete for Life

I write about:

• joint capacity and movement quality;

• strength, power, and speed;

• conditioning and endurance;

• recovery and fatigue management;

• training around injury history;

• the psychology and purpose behind continuing to compete;

• and how all of those pieces fit into one coordinated system.

The goal is not to collect more isolated exercises, recovery hacks, or longevity tips.

The goal is to build a body and a training process that can continue compounding from one season to the next.

Need help applying this to your training?

I coach men over 40 who want to remain strong, athletic, and capable without repeatedly breaking themselves down.

That may mean returning to training after an injury, preparing for a race or event, rebuilding strength, or creating a program that finally accounts for the body you have now.

Learn more about coaching →

You can also reply to any email and tell me:

What are you trying to keep doing—or get back to doing—and what is getting in the way right now?

I read every response.

Steve Bubel

You need a training system that accounts for your goals, injury history, schedule, recovery, and the body you have now.

I coach men over 40 who still want to be strong, athletic, and capable.

Some are preparing for races or events. Some want to return to training after an injury. Others are still working hard but keep running into the same problem: progress builds for a while, something flares up, and the whole process resets.

The issue is rarely a lack of motivation.

More often, the training no longer matches the athlete.

Who this is for

My coaching is for men over 40 who want to:

• keep lifting, running, racing, or competing

• rebuild after an injury or recurring setback

• improve strength, power, conditioning, and movement quality

• prepare for a specific event or physical challenge

• train consistently without repeatedly breaking themselves down

• stop guessing how hard to push and when to pull back

You do not need to be an elite athlete.

You do need to care about remaining capable.

The problem with most programs

Most programs are built around exercises, sets, reps, and weekly schedules.

Those things matter, but they are only part of the picture.

A useful program also has to account for:

• what your goal actually demands

• which tissues and capacities are limiting you

• how much stress you can currently tolerate

• how your training sessions affect one another

• what your work, sleep, family, and recovery allow

• how the program should change when your body gives you feedback

Fitness describes what you can do.

Durability determines whether you can keep doing it.

My job is to help you build both.

How coaching works

We start with an intake process that gives me a clear picture of your goals, training history, injury history, schedule, equipment, and current limitations.

From there, I build a program around your actual situation.

Your training may include:

• strength

• power and speed

• conditioning

• mobility and joint capacity

• movement preparation

• recovery strategies

• event-specific preparation

The exact mix depends on what you are preparing for and what currently limits you.

You receive your training through a coaching app, with exercise instructions, progress tracking, regular check-ins, and adjustments based on your feedback and performance.

This is not a static template handed to you and forgotten.

The program evolves as you do.

What makes this different

I have been training people since my mid-twenties. I am 55 now.

I have spent more than three decades coaching strength, conditioning, movement, and performance. I also continue to train and compete myself.

That matters because the problem I help solve is not theoretical.

I know what it is like to want more from your body while also respecting the history it carries.

I am still lifting, running, and preparing for competition with two torn ACLs, osteoarthritis in both knees, and more than three decades of training history behind me.

The goal is not to prove that limitations do not matter.

The goal is to make better decisions because they do.

That same principle guides my coaching.

We do not lower the standard.

We improve the strategy.

What coaching is not

This is not:

• random workouts

• punishment disguised as training

• endless corrective exercise

• generic fitness programming

• constant intensity for its own sake

• a plan that ignores pain until it becomes a problem

You will still train hard.

The work will simply be organized around what your goals require and what your body can adapt to.

A good fit usually sounds like this

“I know how to work hard, but I am no longer sure how to organize it.”

“I keep making progress until the same area flares up.”

“I want to prepare for something difficult without wrecking myself.”

“I am fit, but my body does not tolerate training the way it used to.”

“I do not want to stop. I want a smarter way forward.”

Interested in working together?

Send me an email and tell me what you are training for, what keeps getting in the way, and what your current training looks like.

I will let you know whether I think I can help and what the next step would be.

Email Steve about coaching →

A person can be strong, lean, well-conditioned, and highly motivated, and still be unable to train consistently.

That sounds contradictory until you separate the two qualities involved.

Fitness describes what you can do.

Durability describes what your body can repeatedly tolerate.

They overlap, but they are not the same thing.

You can have the cardiovascular fitness to run six miles and still have knees that revolt if you do it twice in one weekend. You can be strong enough to deadlift twice your body weight and still have a back that can’t tolerate how your week is organized. You can finish a hard workout, hit a number that looks great on paper, and still be quietly accumulating more stress than you can recover from.

The performance proves you were capable of doing it.

It doesn’t prove you were prepared to absorb it.

After 40, that distinction starts determining whether training compounds or repeatedly breaks you down.

Fitness is easy to see. Durability isn’t.

Fitness leaves evidence everywhere. The weight on the bar goes up. Your mile time drops. You finish more intervals. Your heart rate recovers faster. You finish the event.

These are real outcomes. They show adaptation happened. But they don’t tell you what it cost.

A workout can improve one quality while quietly exceeding the tolerance of another. Your lungs might be ready for more running before your tendons are. Your muscles might be strong enough for a load before your joints are ready for the volume. Your motivation stays high while your recovery capacity is already sliding.

A program can make you fitter and less durable at the same time, sometimes for weeks, before you notice.

Durability is harder to see because it mostly shows up as absence. The knee that doesn’t swell. The Achilles that isn’t stiffer this morning than it was yesterday. The shoulder that tolerates another week of pressing. The back that settles before the next lower-body session.

It’s the ability to repeat a hard effort without dismantling the rest of your week and to come out the other side of a training block with more capacity than you started with, instead of just having survived it.

Durability isn’t the absence of discomfort. It’s the ability to absorb what your goal requires, recover from it, and still be available for the next exposure.

That last part is the one people miss.

The best program isn’t the one that produces the hardest single workout. It’s the one your body can keep adapting to.

Your fastest adaptation can outrun your slowest one

A run doesn’t stress one system. It hits your cardiovascular system, muscles, tendons, bones, joints, and nervous system all at once. None of those adapt on the same timeline.

Your aerobic fitness comes back fast. Your confidence comes back even faster. Connective tissue takes its time.

That mismatch is the trap. The part of you that feels most capable starts setting the pace for the whole system.

Your lungs say you can run farther. Your muscles say you can add load. Your motivation says you should do more. Meanwhile, the knee, tendon, foot, or back is still trying to catch up.

This is exactly why returning athletes so often get hurt right as training starts to feel good again. Their performance capacity comes back before their tissue tolerance does.

The workout feels manageable.

The week isn’t.

Durability is never general. It’s specific to the demand.

Nobody is durable in the abstract. You’re durable relative to something.

A cyclist can log hours of steady-state work and still break down from a modest increase in running. A powerlifter can move enormous loads and still struggle with repeated jumping or changes of direction. A runner can handle high mileage and react badly to heavy lifting.

Someone can be durable enough for three sessions a week and not five. Durable on flat ground and not on steep descents. Fine with steady running and not with sprinting. Able to finish one race but not three across two days.

So the useful question was never, “Am I durable?”

It’s:

Durable enough for what?

Your training has to prepare you for the specific forces, ranges of motion, speeds, volumes, and recovery demands your actual goal requires.

General fitness helps.

Specific tolerance decides whether you can repeat the work.

Pain tells you something, just not the whole story

When something hurts repeatedly, your attention narrows fast. The knee hurts, so the knee becomes the problem. The shoulder hurts, so the shoulder becomes the problem.

Sometimes the painful tissue really is the main limitation. Just as often, it’s simply where a bigger mismatch happens to surface.

The real driver might be:

• too much load added too fast

• too many hard sessions stacked too close together

• insufficient strength in a specific position

• poor tolerance to speed, impact, or eccentric stress

• limited movement options elsewhere in the chain

• fatigue carried from one session into the next

• a goal that’s asking for more capacity than you currently possess

Chase the symptom alone and you may buy temporary relief without changing the pattern that produced it.

Durability is built by identifying what the task requires, finding the part of the system that cannot yet tolerate it, and raising that capacity deliberately.

Recovery won’t rescue a mismatched program

Sleep matters. Nutrition matters. Stress management matters.

None of it is a magic eraser.

You can’t keep exposing your body to more stress than it can handle and expect better sleep, a supplement stack, some mobility work, or an occasional deload to fix the mismatch.

Good recovery supports adaptation to appropriate training stress. It doesn’t make inappropriate stress appropriate.

This gets more important as your margin narrows with age.

When you were younger, you could stack several bad decisions. You could add too much volume, train through a warning sign, place hard days back to back, or change surfaces and mileage all at once, and nothing obvious happened.

It looked like it worked.

Later, those same errors stop disappearing quietly. The body starts talking back.

That’s not fragility.

It’s reduced tolerance for imprecision.

Durable doesn’t mean cautious

It’s easy to hear “durability” and think backing off. Less intensity. More corrective exercise. Less of the training you actually want to do.

That’s not it.

A durable athlete still needs real stress. Muscle needs tension. Bone needs load. Tendons need force. Power needs speed. Conditioning needs physiological strain.

You build tolerance by being challenged, not by being protected from every hard demand.

The difference is dosage. You need enough stress to drive adaptation, but not so much that the cost keeps outrunning the benefit.

Durability isn’t built by avoiding the thing you want to do.

It’s built by progressively earning the ability to keep doing it.

Train the bottleneck, not just the strength

Most athletes gravitate toward what they’re already good at. Strong people like lifting. Runners like running. Competitive people like hard efforts.

Nothing is wrong with any of that, but it’s rarely what determines whether training continues.

Your actual limiting factor might be ankle capacity, single-leg strength, hamstring tolerance, trunk strength, aerobic recovery, sleep, or simply your ability to handle two hard days close together.

The most valuable training in your week is often not the session that sharpens your best quality.

It’s the one that keeps your weakest quality from interrupting everything else.

So change the question you ask after a session.

Not:

“Did this workout improve my fitness?”

But:

“Did this week increase my ability to tolerate the training my goal requires?”

Those are different questions.

A hard session can answer yes to the first and no to the second. That gap is where training programs quietly fail.

The goal is repeatable performance

One great day isn’t the standard.

Repeatable performance is.

Can you train again when it’s scheduled? Can you hold quality across the whole week? Can you progress without resetting every time the same area flares up? Can you finish the block healthy enough to start the next one? Can you chase the event without sacrificing the months that follow it?

After 40, this is where training gets strategic instead of just hard.

You don’t need to prove you can survive one brutal workout. You already know you can.

What you need is a system that lets you train hard, recover, and come back consistently enough for the work to actually compound.

Fitness gives you the ability to perform. Durability keeps that ability available.

You need both.

But when training keeps breaking down, getting fitter usually isn’t the problem to solve first.

Sometimes the missing quality is not more fitness.

It is the ability to tolerate the fitness you already have.

They didn’t.

So this week, real training toward the Dallas Spartan Trifecta Weekend began.

Friday’s lower-body session included a series of maximal resisted sprints on my Technogym SkillRun.

Knees were about a 1 (on a 10 scale) when I started and a 0 when I finished. That was encouraging (and interesting), but it was not the real test.

The real test would come Saturday afternoon, when I tried to run on legs that had already lifted twice and run once that week.

Why runners avoid lifting

Runners often avoid lifting because they assume heavy strength work will leave them too sore, slow, or tired to complete the sessions that matter most. Sometimes they’re right. A high-volume leg workout filled with unfamiliar exercises, slow lowering, and sets taken close to failure can compromise running for several days. Under those conditions, the lifting simply created more fatigue than the athlete could afford.

Done well, it looks nothing like that. The exercises get chosen for their recovery cost, not just their training effect. Sets stop well short of failure. Volume gets sized to what the runner can actually absorb that week, not to whatever a generic template calls for. The legs get stressed enough to adapt, and no more.

That distinction matters to me because at 55, I do not have much recovery capacity to waste. I am preparing for three races over two days and my knees, not my cardiovascular system, set the limit on how much running I can currently tolerate.

So the question this week was not whether I could train hard. It was whether I could create enough strength and power stimulus to improve while preserving the quality of the training it is meant to support.

What I trained this week

The week was built around one priority: develop strength and power without compromising my running.

I trained upper body on Monday, then completed my first lower-body session on Tuesday, combining strength work with resisted sprints on the SkillRun.

On Wednesday, I ran 2.67 miles in just over 25 minutes on my treadmill. The effort was deliberately controlled. My knee score rose from 1 before the run to 2 during and afterward, but the increase remained mild and did not alter my gait or force me to stop.

Thursday was another upper-body session and Friday brought the aforementioned second lower-body day.

Saturday was reserved for the longer run: 6 miles on the SkillRun, a controlled, continuous effort.

On Sunday, instead of running again, I hiked 3 miles with my daughter.

What the label doesn’t tell you

Right now, the priority is rebuilding running and terrain tolerance without giving up the strength and power that may help me preserve performance late in the weekend.

On paper, two lower-body sessions, two resisted-sprint exposures, two runs, and a hike may look like a large amount of leg stress packed into six days.

But the label attached to a workout tells us very little about its actual recovery cost.

A set of trap-bar deadlifts stopped with several repetitions still available is not the same stress as a set taken to failure. A resisted sprint stopped when power output peaks is not the same as continuing until every effort slows. And neither are the same as a high-volume session of lunges, step-downs, and slow eccentric squats.

The purpose of the week was not to make my legs as tired as possible. It was to expose them to force, speed, impact, and repeated locomotion while preserving enough capacity for the training that followed.

That required managing five variables:

1. Exercise selection

2. Eccentric loading

3. Proximity to failure

4. Total volume

5. Placement within the week

For now, much of my lower-body strength and power training is deliberately concentric-dominant. I produce force against the trap bar or SkillRun resistance while minimizing unnecessary lowering and braking work.

That does not mean the week was low in eccentric stress, however. The running and hiking already supplied repeated braking and impact demands. Every running step required my legs to absorb and control force and Sunday’s hike added over 7,000 steps and 420 feet of descending.

The goal is not to eliminate eccentric loading. It is to control where it comes from.

As my tolerance improves, I will add more deliberate eccentric strength and downhill exposure. The race demands it: descending forces the quadriceps to contract while lengthening, absorbing load instead of producing it, which does more mechanical damage per rep than the concentric work of climbing or flat running. In at least one controlled downhill-running protocol, knee-extensor force fell by roughly 25 percent, with recovery requiring several days. That’s exactly the kind of cost I’m not ready to add on top of everything else just yet.

The goal was stimulus, not exhaustion

Exercise selection was only part of the fatigue-management strategy. The other part was knowing when to stop.

Most of my strength work ended with two or three good repetitions still available, what coaches call repetitions in reserve, or RIR. A set completed at three RIR means I believe I could have performed three more technically sound repetitions if I had needed to.

That does not make the set easy. I stop after creating enough tension to support adaptation, but before the final, most expensive repetition, the one most likely to add fatigue, technique breakdown, and joint stress without adding an equivalent amount of useful stimulus.

When training volume is reasonably matched, taking every set to momentary failure does not appear necessary for strength or hypertrophy, but it generally produces more acute fatigue and perceived effort, and may increase muscle damage.

For an athlete whose only goal is maximizing muscle size, training close to failure may sometimes justify that cost. For someone trying to coordinate lifting, running, power, obstacle work, and knee tolerance within the same week, the extra fatigue has to earn its place.

My SkillRun sled sprints used a different version of the same principle. The two tests targeted different portions of the force-velocity spectrum. The heavier resistance emphasized strength-speed: producing relatively high force while still moving quickly. The lighter condition emphasized speed-strength: expressing force at a higher movement speed.

In both cases, I stopped when my measured power output stopped improving. I did not continue simply because I had planned a certain number of sprints or because I still felt capable of doing more. Once the output had peaked, additional repetitions would have produced more fatigue without necessarily producing more peak-power work.

Once output falls far enough, the quality being trained begins to change.

Later in the program, I will allow a small, predetermined decline in power. Spartan racing does not ask for one perfect effort while fresh. It asks me to keep producing useful force after running, climbing, carrying, and accumulating fatigue. At that point, the decline itself will become part of the prescription. For now, the goal is to raise the ceiling. Later, the goal will be to resist falling away from it.

Why this can work

Strength training is often treated as a competing demand in an endurance program: useful in theory, but liable to leave the legs too heavy for the running that matters.

The research does not support removing it so quickly. Heavy and explosive strength training can improve running economy, the energy required to hold a given pace, and may improve running performance even when VO₂ max changes little. Strength work may not enlarge the aerobic engine, but it can help the athlete use that engine more efficiently.

A productive strength stimulus and an unnecessarily exhausting workout are not the same thing.

Many runners experience the worst possible introduction to concurrent training. They add unfamiliar walking lunges, Bulgarian split squats, slow negatives, high-repetition squats, or plyometrics to an already full running schedule. The exercises are new, the volume is high, the sets finish close to failure, and the long run arrives before the legs have recovered. Then they conclude that lifting makes them worse runners.

The problem may not be strength training. It may be the version of strength training they selected.

What happened when the weekend arrived

The strength work had done its job only if the running still worked.

Saturday’s longer run was therefore a test of performance retention. I wanted to know whether Friday’s lower-body work had left behind the kind of fatigue that undermines performance: unusually heavy legs, deteriorating mechanics, an elevated effort at a familiar pace, or knees that became progressively more irritated.

I ran 6 miles on the SkillRun in 60 minutes and 48 seconds. My knee score was 2 before the run. During it, the discomfort rose briefly to 4 before settling back to 2. It remained at 2 afterward.

The run was not symptom-free, and I don’t want to spin it as proof that Friday’s work had no effect. But the discomfort eased rather than compounded, and my stride and effort stayed unaffected. By the end, the knees had returned to where they started.

The more useful observation was that Friday’s strength and sprint work did not produce the deep soreness or loss of function I would expect from a higher-volume, eccentric-heavy leg session. I could still complete a meaningful aerobic run rather than merely survive one on compromised legs.

Sunday’s hike added more than an hour on my feet and some controlled downhill exposure without becoming another hard cardiovascular session. It extended the weekend training while keeping the cost manageable.

What runners can take from this

The lesson is not that runners should avoid eccentric exercises, lift only with a trap bar, or perform sled sprints on a specialized treadmill. It is that strength training should be designed around the athlete’s recovery budget.

Choose exercises by recovery cost, not tradition. A movement does not deserve a place in the program simply because it is considered a good exercise. Walking lunges, split squats, step-downs, slow eccentric squats, and plyometrics may all be useful. They may also create more residual fatigue than the athlete can currently absorb. Their dose, timing, and novelty are what matter.

Stop before the set becomes disproportionately expensive. Most working sets do not need to reach failure. Two or three repetitions in reserve can provide meaningful strength work while leaving more capacity for the next run. Technique loss, pronounced slowing, or rising joint symptoms can also end a set regardless of the number written in the program. The question is not simply whether you could perform another repetition. It is whether that repetition would improve the intended adaptation enough to justify what it may take away from the next important session.

Give power training an output-based stop rule. Power work needs to remain powerful. When output plateaus or begins to fall, continuing may turn peak-power training into fatigue tolerance or conditioning.

Manage volume before removing strength. The problem may be too many exercises and sets, not the presence of lifting itself. Before cutting strength training from an endurance plan, reduce its cost:

• Use fewer hard sets.

• Keep most sets shy of failure.

• Avoid large doses of unfamiliar eccentric work near the long run.

• Choose exercises with a favorable stimulus-to-fatigue ratio.

• Place the highest-cost session farthest from the key endurance work.

Judge the arrangement by what happens next. Soreness is useful information, but it is not a complete measure of recovery. An athlete may feel little soreness and still show lower power, altered mechanics, higher effort at a familiar pace, or rising joint symptoms. The better test is performance retention. Did the next run still look and feel like running?

What the week showed

The week did not prove that strength training will never interfere with my running. It showed that this particular dose did not appear to.

Running and hiking already supplied plenty of impact and braking work. The strength sessions trained force and power without needlessly adding to that cost. That is the standard I will keep using.

Strength work stays if it makes me more capable without degrading the sessions that determine whether I am prepared for October.

The next challenge will be more expensive. I still need to build the downhill tolerance the race demands without provoking the knees that limit the entire plan.

The goal is not to avoid fatigue. It’s to spend it where it buys the adaptation I need most.

That question carries more weight than it once would have.

I have completed more than 30 Spartan races. I have stood on age-group podiums six times. In 2023, I won my age group at the Austin Spartan Super 10K.

But time can be a bitch.

At the last race of 2024, a Spartan Sprint I ran with my daughter, sharp pain flared on the outside of my left knee and forced me to walk almost the entire course. For a while after that, I wondered if my racing days were over.

I still do.

I’m 55 now, and both of my knees are garbage. I have two torn ACLs: the right one on Thanksgiving Day in 2014, the left one years earlier, skiing in college. Neither was surgically repaired. They have carried me through years of lifting, running, trail races, and Spartan racing since, and they have also made it clear that fitness does not grant unlimited tolerance. Both get worse with higher running volume.

But, damn, I miss it. Nothing clears my head like a race does: no past, no future, just the obstacle I’m on or the pain I’m in. And, if I’m being honest, I miss the training just as much as I miss the racing itself. The focus, the dedication, the discipline, all make me a better trainer, husband, and father.

And that is why I want back in.

I recently coached someone else through a Trifecta Weekend. I’ve never done one myself, and I can’t leave the challenge unfinished. Three races, two days, in twelve weeks is now the plan. Will my knees cooperate? Can I protect them enough to find out?

Ten weeks ago, I ran Spider Mountain, 11.63 miles with steep, punishing downhills that beat my knees up badly. Two comeback attempts since then had both failed: an interval session on June 6 (”Right knee shut me down on the 2nd hard interval”), and a Billat RABIT test on June 14 (”My knees, right in particular, were killing me. Couldn’t finish.”). Bleachers had been about as close as I’d come to running lately.

This time, with a new goal in front of me and more rest behind me, I needed to know two things: whether my knees could handle running again at all, and whether they could handle it on back-to-back days, since that’s exactly what race weekend will demand. Yesterday and this morning were the first true running since Spider Mountain.

After a couple months off, the pain in my right knee had dropped to zero out of ten. The left was a two. Nothing changed while I ran. Afterward, both knees sat around a two. My legs were sore, the ordinary soreness of two conservative efforts back to back, but the soreness was muscular. The knees themselves didn’t feel like they were asking me to stop.

That was the test. Not a training run, but the answer to a smaller and more important question: whether I should even attempt this experiment at all. If two runs in two days had left my knees worse off than I found them, twelve weeks of training toward a Trifecta weekend would have been the wrong project to start.

They didn’t. I passed the first test.

Next week: the actual plan. How much running I really need, why OCR changes the mileage equation, and the rules that decide whether I move forward or hold back. After that, I’ll be reporting from inside the training: what’s working, what isn’t, and what the data says.

A 49-year-old triathlete recently reached out to me after reading one of my articles.

He has been racing triathlons for five years, has completed a full IRONMAN, and is now chasing Kona. He is already training consistently: three swims, three bike rides, and three or four runs most weeks.

His endurance coach does include some strength work, but it is generally 20 to 30 minutes of mostly bodyweight exercises. He has never trained seriously or consistently with weights and wanted to know: what would a more structured strength program provide that he is not already getting?

It’s a reasonable question.

The answer is not simply “harder workouts.” And it is certainly not more fatigue for the sake of feeling productive. The goal is to build the physical qualities that allow an endurance athlete to absorb training, maintain performance under fatigue, and continue competing well as he moves through his 40s, 50s, and beyond.

The endurance engine is only part of performance

Endurance athletes naturally spend most of their time developing the cardiovascular and metabolic systems required by their sport. But race performance depends on more than the size of the aerobic engine. It also depends on the physical structure carrying it: muscle strength, tendon capacity, joint control, force production, movement efficiency, and fatigue resistance all influence how much of an athlete’s fitness can actually be expressed, especially late in a race. All three disciplines draw on these qualities, but the research is clear on which one carries the most weight in the final result.

A 2026 systematic review of 86 studies on IRONMAN 70.3 performance found that cycling was the strongest predictor of overall race time as it accounts for the largest portion of the race and influences how much running capacity remains afterward. Although the review was conducted on 70.3 racing, the same bike-to-run relationship holds at least as strongly over a full IRONMAN, where pacing errors and local muscular fatigue have even longer to accumulate.

A fast bike split is not necessarily a good bike split. A good bike leg is fast enough to be competitive and controlled enough to preserve the run: producing force efficiently, holding a sustainable position, regulating intensity, and reaching the final discipline without having spent every available resource. Those demands are not purely aerobic. They also depend on strength, postural endurance, and fatigue resistance, which is part of what a structured strength program is built to provide.

Running is where aging shows up most clearly

The same review found that running performance declines most sharply with age. Cycling remains comparatively stable, while running is more affected by reductions in aerobic capacity, muscle mass, neuromuscular function, and the cumulative demands of weight-bearing impact.

Running alone may not preserve all the qualities required to keep running well, or to run faster. As athletes age, they gradually lose muscle mass, maximum strength, power, tendon stiffness, rate of force development, and neuromuscular efficiency. Endurance training can slow some aspects of that decline, but it does not fully protect against all of them. A large volume of low-intensity endurance training may leave some of these qualities undertrained entirely.

That is where strength training becomes increasingly valuable. Not because the athlete wants to become a powerlifter. Because strength and power are part of the infrastructure of endurance performance.

Strength training should not compete with endurance training

Another question I often get is: how do you actually fit strength training into a schedule that’s already full?

Many endurance athletes are hesitant to lift because they assume it will make them sore, heavy, or too fatigued to complete their important sessions. Time is the other worry: where do two more sessions come from in a week that’s already full swimming, biking, and running? That concern is legitimate when strength training is programmed poorly. A strength program should not simply be placed on top of an already demanding endurance schedule. It should be integrated into it.

This athlete is already completing nine or ten endurance sessions per week. Adding two high-volume powerlifting or bodybuilding workouts would be foolish. The goal is two targeted sessions that complement his swim, bike, and run work without creating unnecessary recovery debt. Those sessions might last 30 to 45 minutes, not dramatically longer than the time he's already spending on bodyweight work, and could be shortened during higher-volume or race-specific phases. The difference is not the time on the clock. It is what happens inside that time: progressive loading, exercises chosen from what an assessment reveals, and a clear target instead of a generic circuit. For one athlete that means calf and soleus capacity. For another it's hip strength and trunk endurance. For a third, it’s shoulder function and tolerance of the aero position.

Bodyweight training is not useless

Bodyweight exercises can be effective. They can improve coordination, movement quality, muscular endurance, and general fitness. They are convenient, accessible, and often appropriate for beginners. But the body adapts to the demands placed upon it, and quickly. At some point, repeated sets of air squats, lunges, bridges, planks, and push-ups may stop providing enough overload to create meaningful improvements in strength or force production. The issue is not that bodyweight work is bad. The issue is whether the program progresses.

An athlete chasing Kona does not merely need to move. He needs to become measurably more capable, and that usually requires progressive loading: more resistance, greater range of motion, better unilateral control, increased force, more difficult variations, improved tendon capacity, greater power. Without progression, strength training can become little more than a warm-up.

The two primary goals: durability and force production

A useful endurance-strength program should accomplish two things simultaneously.

1. Build durability

Durability is the ability to tolerate training and maintain performance as fatigue accumulates. For a triathlete, that may include calf and soleus strength, Achilles tendon capacity, hip and knee strength, hamstring strength, unilateral control, trunk stability, upper-back strength, shoulder function, and the ability to maintain posture.

Durability does not mean becoming injury-proof. No program can guarantee that. It means increasing the athlete’s physical capacity so that the demands of training occupy a smaller percentage of what the body can tolerate. When capacity rises, the same training load may become less threatening.

2. Improve force production

Endurance performance still requires force. Every swim stroke, pedal stroke, and running stride requires the athlete to produce force against the water, the bike, or the ground. Stronger athletes may be able to produce the required submaximal force using a smaller percentage of their maximum capacity, which can improve economy and reduce local muscular fatigue.

For a triathlete, this shows up first on the bike. Building maximal strength lowers the percentage of available force a rider needs for each pedal stroke, but only when that strength is trained alongside the bike itself. Strength that never transfers to the saddle does not improve economy on its own. Integrated correctly, it leaves more in reserve for the back half of the ride and for the run that follows. An IRONMAN bike leg is 112 miles and can take most age-groupers between five and six hours. Holding an aero position for that long depends on strength as much as it depends on bike fit and postural endurance. Since cycling is the single strongest predictor of overall finish time, force production gained here does not stay on the bike. It carries straight into the run. The purpose is not to turn an endurance athlete into a maximal-strength specialist. It is to raise the ceiling so race-level force becomes relatively easier, on the bike most of all.

Coordination between coaches matters

This athlete already has an endurance coach. That is not a problem. In fact, it can be an advantage when roles are clearly defined. The endurance coach may oversee swim volume and intensity, bike development, running progression, race-specific preparation, pacing, tapering, and overall endurance load. The strength coach may oversee strength, power, joint capacity, tendon loading, movement assessment, corrective priorities, and progression of resistance work.

The mistake would be for both coaches to operate independently. A heavy lower-body session placed before a key brick workout could undermine the athlete’s race preparation. A high-volume strength block added during peak endurance volume could create fatigue without providing enough time for adaptation. The programs must communicate. Strength volume should rise and fall according to the endurance calendar. During general preparation, there may be room to build strength more aggressively. During race-specific preparation, the goal may shift toward maintaining strength with less total volume. Good programming is not about proving which coach’s training matters more. It is about making the pieces work together.

More training is not always the answer

The same review cites full-distance research showing that increasing weekly training volume beyond 14 hours did not consistently produce better performance. That does not make 14 hours a universal ceiling, but it does challenge the assumption that more volume automatically creates more progress.

That should matter to the masters athlete. When progress stalls, the instinct is often to add more. Another ride. Another run. More mileage. A longer weekend session. But the limiting factor may not be insufficient endurance volume. It may be that the athlete lacks the strength, tissue capacity, recovery, or mechanical efficiency to benefit from additional volume. Adding training to a system that cannot absorb it does not create adaptation. It creates debt.

The real value of strength training after 40

A well-designed strength program does not promise that an athlete will never get injured or never slow down. It does something more realistic. It gives the athlete a better chance to preserve the qualities that endurance training alone may gradually allow to decline: muscle mass, maximum strength, power, tendon capacity, bone health, running economy, force production, movement options, confidence under load.

Those qualities do not matter only in the gym. They affect how an athlete climbs, accelerates, absorbs impact, maintains posture, tolerates fatigue, and continues training year after year.

You may not need harder workouts

You may need more specific ones. The endurance athlete does not need random intensity. He does not need to finish every strength session exhausted. He does not need soreness as proof that the workout worked. He needs the minimum effective dose of the right training: training that strengthens the tissues most exposed to load, training that improves force without compromising key endurance sessions, training that progresses over time, training that fits the athlete he is now and the athlete he intends to remain.

The best strength program for an endurance athlete is not one that competes with the sport. It is the one that allows him to keep doing the sport, and express more of his fitness when it matters. Because after 40, the goal is not simply to build a bigger engine. It is to make sure the chassis can still carry it.

Then someone got the last word, and it was the fairest point in the whole thread: at the average level, endurance really is easier to fake your way into. Anyone can half-ass his way to a slow marathon in 6 months. That won’t build you an impressive physique.

But that argument still misses the point. “Which is harder?” is the wrong question entirely.

Hypertrophy, strength, and endurance hit their ceilings for different reasons, on different timelines. Lumping them together is why this argument keeps going in circles. How fast each ceiling arrives, and how long you can keep climbing before you hit it, is what changes how you train from here on out.

Early progress doesn’t tell you where any of these ceilings actually sit. A 20-year-old novice has room to grow in all three directions at once: muscle, strength, and endurance move together for a while. A man in his 40s or 50s with real training years behind him almost never has that luxury. One of these three ceilings is usually much closer than the other two, whether he’s noticed it yet or not.

The hypertrophy ceiling: the one you hit first

Muscle mass has the closest ceiling of the three, and it’s the one ceiling you can’t program around or push through. The timeline is well-mapped. Year one, an untrained male gains 15 to 25 pounds of lean mass. Year two, roughly half that. Year three, half again. By year five, you’re fighting for a pound or two per year. Alan Aragon’s model, Lyle McDonald’s model, and Casey Butt’s formula all converge on the same picture: 3 to 5 years of proper training gets a natural bodybuilder to 80 to 90% of his genetic potential. The last 10 to 20% takes another decade. Even then, the gains are marginal.

Fat-Free Mass Index tells the story cleanly. Among natural bodybuilders who’ve trained hard for years, FFMI settles into a range of 22 to 25 kg/m², the ceiling for men who’ve actually gone after it, not a number most men will ever get near. Anything above 25 is either elite genetics or a needle. Muscle fiber count is fixed at birth, and no amount of training adds more of it.

Past 50, it gets worse. Anabolic resistance sets in: muscle protein synthesis response to training drops, along with testosterone. In one 6-week study, older subjects gained only about a third of the muscle thickness their younger counterparts did on the same program.

Hypertrophy is hard because once you hit the ceiling, nothing moves you past it, and you hit it fast.

The strength ceiling: still climbing after hypertrophy stops

Strength has a longer arc because it isn’t just about muscle size. It’s neural drive, motor unit recruitment, tendon stiffness, and force transmission through connective tissue, adaptations that mature far slower than muscle does.

World-class powerlifters peak in their mid-30s, a decade or more after most natural bodybuilders have already hit their muscle ceiling. That’s the whole point: strength keeps climbing long after hypertrophy has hit its wall. The 5 years before peak alone show a 12% total improvement, driven largely by neural drive, technique, and connective tissue finally catching up.

Tendons are the slowest tissue to adapt. Meaningful strength improvement takes 6 to 24 months of progressive loading, and the full remodel continues for years after. That’s why aging lifters who push past what their connective tissue can handle end up with elbow tendinopathy, patellar issues, and shoulder problems.

Strength is hard because the neural and structural adaptations take decades to fully express.

The endurance ceiling: it’s not just VO2max

Most world-class long-distance runners need 8 to 10 years of systematic training before reaching international standard. Elite marathoners train 500 to 700 hours a year, 10 to 15 hours a week, 11 months a year.

But here’s what most people miss: VO2max isn’t the ceiling. It plateaus within 4 to 12 months of consistent high-intensity training. Once your heart hits its structural stroke volume limit, VO2max is largely done improving. Lactate threshold keeps climbing. Running economy improves for years, sometimes decades. Fatigue resistance, fueling capacity, thermoregulation, mitochondrial density, capillarization, and fiber-type shifts all continue to adapt. One 12-year case study of a British marathon runner showed velocity at VO2max climbing 15% and lactate threshold 13 to 19%, while VO2max stayed flat.

Elite endurance athletes peak in their mid-30s because they learn to use the engine they already have, not because they build a new one. There isn’t one ceiling. There’s a stack of them, each with its own trainable timeline.

That’s what makes endurance hard: the volume required to keep improving is enormous, unrelenting, and multi-dimensional.

Comparing the three ceilings

Hypertrophy is a steep hill with a hard wall at the top. Fast progress, then it stops. Strength is a long, gentle climb, slower per year, but the road keeps going. Endurance is a mountain range: you summit the first peak, VO2max, fast, then discover five more peaks waiting: threshold, economy, fatigue resistance, fueling, thermoregulation.

Start with what’s true across all three: elite is elite. Hard is hard. Reaching a natural FFMI of 25, a 600-pound raw squat, or a sub-3 marathon all put you in rarefied territory among people who’ve already dedicated years to the pursuit. Nobody backs into any of these by accident. That’s not where they differ.

Here’s what makes the hypertrophy wall different. Natural lifters chasing the practical hypertrophy ceiling need something like 1,500 hours to get there. Elite powerlifters and endurance athletes need four to five times that, somewhere in the 6,000 to 8,000 hour range, to reach their own peaks. By raw time investment, hitting your own hypertrophy ceiling costs far less than reaching elite status in strength or endurance.

And it’s also the ceiling almost nobody crosses. The study that first drew the line at a natural FFMI of 25 tested 74 already-serious natural athletes. None of them got past it. The exceptions are outlier genetics, the same handful of pre-steroid-era champions who sit above 27. A 600-pound raw squat sits above the 90th percentile of competitive, drug-tested powerlifters, rare among men who already devote their lives to the sport, but not blocked by genetics the way FFMI 25 is. Roughly 4% of male marathon finishers break 3 hours: rare, but real, same story. Crossing hypertrophy's ceiling is rarer than either. It's the one wall effort alone doesn't move, for almost everyone who hits it.

That’s not because strength and endurance lack genetic ceilings of their own. Of course they do. Nobody has unlimited squat capacity or unlimited VO2max. The difference is what kind of ceiling each one is. Hypertrophy runs through plenty of separate biological processes: satellite cell activity, protein turnover, mechanotransduction. They all point at the same outcome though: how much muscle tissue you can add. That's one number to max out, and you get there fast because there's nowhere else to find more. Strength is neural drive, motor unit recruitment, tendon stiffness, and connective tissue force transmission stacked on top of each other, each maturing on its own clock, several of them taking years longer than muscle ever does. Endurance stacks the same way, just longer: VO2max plateaus in 4 to 12 months, faster than hypertrophy, if it were the whole picture. It isn’t. Everything layered on top of it keeps improving for years after VO2max plateaus.

Hypertrophy takes the fewest hours because there’s only one wall to hit, and you hit it fast. Strength and endurance take longer because they aren’t one wall. They're several, each one topping out on its own timeline, which is why almost nobody trains long enough to run out of room in either one.

The wall you’re already standing at

None of this is a choice you get to make from scratch. If you’ve trained for a decade or more, you’re not picking which ceiling to chase. You’re already standing closer to one of these three walls than the other two, whether you’re aware of it or not.

Here's how you'd know. If your body composition hasn't meaningfully changed in three years of consistent training, that's your hypertrophy ceiling talking, and no amount of extra volume moves it. If your numbers on the big lifts are still climbing, even slowly, strength still has room. If your times are still coming down, even by seconds, endurance still has room. Most men with a decade or more of training age are already at one wall, with real room still open behind one of the other two. The mistake is training all three the same way, like none of them have a ceiling yet.

Spend your hours where they still buy you progress.

Most endurance training calendars are built around what adapts fastest. The cardiovascular system responds in days. Muscle protein synthesis peaks within hours of a hard session. VO2max shifts in four to six weeks. Those timelines feel like the body’s schedule, so training programs run on them.

Tendons don’t.

Tendon collagen turnover runs on a 12- to 14-week cycle. The structural adaptations that determine whether a tendon gets stiffer, stronger, and more capable of doing its job take three months to accumulate, and only when training is designed to drive them. Most endurance programming doesn’t account for that.

The size problem

There’s a reasonable belief that running builds tendons. Indeed, running does add volume. A 2016 study by Stenroth et al. published in the Journal of Applied Physiology measured tendon properties in 74-year-old masters athletes (elite endurance runners and elite sprinters, both with an average of 42 years of consistent training) and compared them against age-matched untrained adults and young untrained controls.

The endurance runners had Achilles tendon cross-sectional area 45% larger than young untrained adults. The sprinters were 71% larger. Decades of running produces impressive tendon hypertrophy.

Stiffness was a different story. Across all the older groups (athletes and sedentary controls alike), Achilles tendon stiffness showed no significant between-group differences. Young’s modulus, the measure of how well tendon material actually handles load at the tissue level, was 31 to 44% lower in all older groups compared to young adults, regardless of training history.

Volume built the tendon bigger. It did not build it stiffer. Bigger without stiffer is a tendon that occupies more space but deforms more under load. That’s not a performance asset. That’s a structural compromise. One that ends in tendinopathy, or worse.

Why stiffness is the variable you should care about

Tendon stiffness determines how efficiently the muscle-tendon unit transfers force. A stiffer tendon deforms less with each loading cycle, which means force gets to the ground faster, with less energy lost in the spring. For runners, this translates directly to running economy, the oxygen cost of maintaining a given pace.

Werkhausen et al. (2019) demonstrated the mechanical consequence of this in a 10-week isometric training study. An 18% increase in Achilles tendon stiffness through targeted loading reduced how much the tendon deformed during each running stride by 30%. That shift altered the timing and magnitude of energy return at push-off. The muscle doesn’t have to work as hard to produce the same propulsive force. Over thousands of steps, that’s the difference between a runner who fades and one who doesn’t.

Stiffness doesn’t accumulate from mileage. It accumulates from specific load applied at the right intensity over enough time.

The middle-aged collagen problem

A 2024 study by Nulty et al. in the American Journal of Physiology used a crossover design: the same resistance-trained men averaging 49 years old completed a heavy lower-body session three times, once with no supplementation, once with 15 grams of hydrolyzed collagen, and once with 30 grams. Collagen synthesis was measured via blood markers after each session. When they trained with no supplementation, collagen synthesis showed zero change from baseline.

The researchers named this finding connective tissue anabolic resistance: a specific reduction in the collagen synthesis response to exercise in middle-aged men. The muscles still responded. The connective tissue didn’t get the signal. Not until collagen was added to the equation. The dose mattered: thirty grams produced a meaningfully greater synthesis response than fifteen.

The same research group published a 12-week intervention in 2025 in the European Journal of Sport Science. Men averaging 47 years old completed twice-weekly resistance training for 12 weeks. One group received 30 grams of hydrolyzed collagen plus 50 milligrams of vitamin C after training. The other received placebo.

Muscle and strength gains were identical between groups. Tendon adaptation was not. The collagen group saw patellar tendon stiffness increase by 661 N/mm. The placebo group: 247 N/mm. Tendon cross-sectional area grew six times more in the collagen group and the quality of the tendon material itself improved more than twice as much.

The collagen supplement did not touch muscle. It specifically and measurably accelerated tendon remodeling, in the exact population where the baseline signal is blunted.

What the training calendar gets wrong

The standard masters training calendar sequences load by duration and intensity: easy weeks and hard weeks, a build phase and a taper. What it does not sequence is connective tissue. A 12-week collagen turnover cycle requires 12 consecutive weeks of the right stimulus to complete. Running-focused training rarely provides that stimulus deliberately, and when a training block ends or gets interrupted by a race, a taper, or travel, the clock resets.

The loading type matters. Mileage loads the tendon in a repetitive, low-force pattern that builds cross-sectional area without changing material properties. Heavy and slow resistance training, and isometric work at high force outputs, drive the stiffness adaptations. These are different stimuli producing different structural outcomes. Most endurance programs only deliver one of them.

A note on eccentric loading: the Alfredson protocol (heel drops off a step, high volume, pure eccentric) has 20 years of clinical evidence behind it and it works. The mechanism is slow loading under high tension sustained long enough to drive collagen turnover. Heavy slow resistance (HSR) captures that same mechanism and adds the concentric phase, which is why RCTs comparing the two produce equivalent or better outcomes with HSR. Eccentrics are not wrong; they are a subset of the broader loading principle. HSR is the fuller application of it.

The protocol that has produced consistent tendon stiffness gains in the research combines three approaches, sequenced across a 12-week block:

1. Heavy slow resistance (twice weekly, weeks 1–12): Compound lower-body movements (squat, leg press, single-leg variations) performed at loads progressing from 55% up to 85–90% of 1-repetition maximum. Tempo is the critical variable: 3 seconds down, 2-second pause, 3 seconds up. The slow tempo keeps the tendon under sustained tension long enough to drive collagen synthesis. Four sets per exercise, 6–10 reps. This is the loading structure Agergaard et al. used in their 12-week patellar tendinopathy rehabilitation trial, where structural improvements were still measurable 3 to 4 years after the intervention ended.

2. Isometric work (added to the same sessions, weeks 1–12): Plantarflexion or leg press holds at 70–80% of maximal effort, 5 sets of 45-second holds with 2 minutes rest between sets. The Werkhausen et al. protocol used explosive onset, 1-second holds with 5-second rest between reps; that format maximizes stiffness adaptation while minimizing muscle hypertrophy. Both formats load the tendon at high force with minimal joint movement, which is the mechanical signal for stiffness change.

3. Plyometrics (introduced in weeks 7–12 only): Pogo hops, drop jumps, and single-leg bounds apply high tendon forces at short contact times. The force rate is what matters: the tendon encounters similar demands during running, but plyometric loading reaches magnitudes running alone never produces. This is the stimulus for rate-sensitive stiffness, the tendon’s ability to resist deformation rapidly rather than just under sustained load. Introducing plyometrics before the structural base is established in weeks 1–6 puts a high-rate demand on tissue that hasn’t yet adapted to handle it. The sequence is not optional.

Supplementation sits on top of this loading structure:

Collagen timing: 15–30 grams of hydrolyzed collagen with 50 milligrams of vitamin C, taken around each training session. The Nulty 2025 trial delivered it post-training and produced significant tendon adaptation at that timing. The case for pre-training delivery is mechanistically plausible but not yet tested in a controlled trial: collagen synthesis peaks in the first hour after a loading bout, and having the amino acid pool elevated before that window opens should amplify the response. That inference is coaching reasoning built on the mechanism, though, and not a study conclusion.

The weakest link rule

A 50-year-old runner with excellent cardiovascular fitness and a tendon that never fully adapted to his training load is not limited by his VO2max. He’s limited by the tissue that hasn’t caught up.

Training will continue to build on top of that gap until the gap closes, or until the tendon decides for him that it’s time to stop.

That’s the finding buried inside a systematic review and meta-analysis just published in Frontiers in Physiology — 46 studies, 1,280 participants, every one of them comparing how older and younger muscle responds to the same anabolic signals.

The part nobody quotes

Post-exercise muscle protein synthesis showed no significant age-related difference in five of eight studies. When exercise was combined with protein intake, seven of nine studies showed no difference between young and older adults.

The findings that do get quoted: resting muscle protein synthesis is modestly lower in older adults and post-meal protein synthesis is also reduced. When you eat protein, the anabolic response is attenuated compared to a 25-year-old.

Those are real effects. They’re just not the whole story.

Breakdown isn't the problem

The researchers tracked muscle protein breakdown across every condition: post-meal, post-exercise, and combined. Breakdown rates were unchanged with age. Most studies reported no difference at all.

Your body isn’t tearing down muscle faster. The building signal has gotten quieter. The mTOR pathway — the primary molecular switch for muscle protein synthesis — still activates. It needs a stronger input to fire fully. Part of what drives that is reduced sensitivity to leucine at the cellular level. Part of it is a temporal shift — older muscle shows a delayed anabolic response after combined exercise and feeding, with synthesis rising later in the recovery window rather than immediately after. The machinery runs the same sequence. It runs it on a different clock.

What to actually do with this

Leucine content matters more than total protein grams. Katsanos et al. (2006) found that older adults matched younger adults’ protein synthesis response when given an amino acid mixture with 41% leucine content, but showed a significantly lower response when leucine dropped to 26%, with total protein held roughly constant. Whey, eggs, and meat are high-leucine sources. If you supplement, check leucine content, not just total grams.

The per-meal dose needs to go up. A retrospective analysis of 108 participants (Moore et al., 2015) found that muscle protein synthesis in older adults plateaus at roughly 0.4g of protein per kilogram of bodyweight per meal — around 33g for a 180-pound man. The 20g recommendation you’ve seen everywhere was built on younger populations, whose plateau sits closer to 0.24 g/kg. Targeting 40g post-training puts you above that threshold with room to spare.

Training volume and load interact differently in older muscle. Kumar et al. (2009) found age-related differences in MPS at high loading schemes (60–90% 1RM), with younger adults outpacing older ones. The same group later showed that doubling set volume at lower loads (40% 1RM) eliminated that gap entirely, while higher loads at moderate volume produced no age-related difference at all. What this means practically: older muscle responds to mechanical work, but the dose-response curve has shifted. You need either higher volume or higher load to reach the same synthetic output a younger athlete gets from a standard session. Protein timing compounds this — the delayed anabolic response in older muscle means the feeding window after training is wider than the literature built on younger athletes suggests. Don’t rush the post-training meal, but don’t skip it either.

Knowing this changed how I program and what I put on my plate. It should do the same for you.

Worth noting: this is acute data. The studies measured protein synthesis over hours, not muscle gained over a training cycle. The inference is reasonable. It isn’t proven.

This week I assessed a second runner. Different athlete, different injury — a recent right-sided Achilles he’d been self-treating with a protocol that didn’t fit his specific problem.

Different side. Similar pattern.

His original question, when he first reached out to me: “Do you work with runners to improve their elasticity and spring? Short-contact plyos and strength work?”

Good question when your joints and tendons are ready. For him — and for most runners over 40 — it was the wrong place to start.

He was thinking about outputs — ground contact time, stiffness, pop — the performance qualities you can see and measure. I needed to back him up to inputs: what his hip, ankle, and Achilles could actually tolerate, repeatedly, without leaking force or breaking down. You can’t reliably improve the output if the inputs aren’t there.

Restricted ankle dorsiflexion on the right. Restricted hip abduction on the right. In his hip assessment you could see the compensation — his ankle recruiting to help drive hip flexion, his trunk shifting to manufacture abduction range his hip couldn’t express on its own, effort written all over his face.

He’d been treating the Achilles. Nobody looked at what was driving the load into it.

Two runners. Opposite sides. Different injuries. One principle: if joint dysfunction exists, training is just making the dysfunction stronger.

Getting stronger at the wrong things

Most runners who care about strength train like the second runner: squats, deadlifts, lunges, plyometrics. Load the patterns, build the posterior chain, get more spring. The research is clear that well-designed strength work improves running economy, so the logic seems sound.

The limitation is that pattern training loads whatever is already there. If compensation is present, the training reinforces it.

A hip that can’t internally rotate on one side will still squat — by dumping motion into the lumbar spine or letting the knee cave. A stiff ankle will still lunge — by lifting the heel, tipping the chest, or loading the medial knee and Achilles. An asymmetric pelvis will still deadlift — with one hamstring and one glute working overtime while the others coast.

From the outside the pattern looks fine. The load goes up. The numbers improve. You get stronger.

The glute that isn’t contributing in mid-stance doesn’t suddenly join the party because you added weight to a squat. The hip that can’t abduct cleanly doesn’t recover that range because you stacked clamshells on top of a joint that still can’t get into position. The Achilles that’s been overloaded for months doesn’t become more resilient if the joint restriction driving that overload is still there.

You’re getting stronger at compensating.

Joints and connective tissue adapt on a different timescale

Muscle and neural adaptations show up in days to weeks. Tendons, ligaments, and joint capsules adapt over months — and for runners over 40, that mismatch is amplified. You can increase your deadlift or your weekly mileage in six to eight weeks. Your connective tissue capacity is still catching up three, six, twelve months later.

When you stack pattern-based strength on top of that — heavy lunges, split squats, plyos — without first confirming the joints can get into and out of those positions, two things happen simultaneously. Your nervous system leans harder into the compensations it already has. And your tendons and joints absorb more load at the exact angles they're already being overloaded in.

It doesn’t matter whether the load comes from a barbell or a 100-mile week. When the joints can’t do their jobs, everything above and below them compensates. Stack enough load on top of that — in the gym or on the road — and the tissue with the least capacity fails first.

That’s how you get a 100K hamstring blow-up at mile 31. That’s how you get an Achilles that fails on day six of a big mileage week.

The second runner had been averaging 7 to 9 hours of running per week. The week it broke down he ran 100 miles — roughly 13 hours on his feet. “Too much, too soon,” he told me. “Classic.”

The joint restriction had been quietly compounding stress on that tendon for years. The load spike didn’t create the vulnerability. It revealed it.

These asymmetries don't start with running. You can see them in kids, field sport athletes, and lifters who have never laced up a pair of running shoes. The sport doesn't create the pattern — it exposes it.

Start here

You don’t need a formal assessment to start paying attention to your joints.

Controlled Articular Rotations — CARs — are slow, active circles that take each joint through its full available range under muscular effort. Not passive stretching, not momentum. You’re actively moving the joint while keeping everything else still. Developed by Dr. Andreo Spina within the Functional Range Systems framework, they work as both a training tool and a daily diagnostic — a way to maintain joint health while generating a real-time readout of how that joint is functioning.

Take five minutes and move each hip through its rotational range.

What you’re looking for: asymmetry between sides, pinching or compression at end range, a hip that has to recruit the ankle or trunk to complete its arc. These are signals most runners never notice because they’ve never been taught to look for them. You don’t need to interpret what you find — you just need to notice whether both sides feel the same, and whether they feel the same today as they did last week. Hips that feel consistently worse than they did three months ago are telling you something, even when your running still feels fine.

The sequence that works

Joint-first training lives below the pattern level. The questions change: not “Can you squat?” but “What can this hip do on its own?” Not “Can you lunge?” but “What can this ankle express in dorsiflexion without the knee or trunk compensating?” Not “Can you bound?” but “Can your pelvic control and Achilles tolerate the landing angles you’re about to practice a thousand times?”

The Functional Range Systems model works in that order — joint first, tissue second, strength and movement patterns third. The point isn’t a better exercise program; it’s starting where the problem actually lives.

Three components:

Mobility — not how far someone can push you into a stretch, but how much range a joint can actively express and control under its own power.

Control — whether you can own that range slowly, with precision, without compensating elsewhere.

Load Capacity — how much force the joint and its connective tissues can absorb and transmit, not just at the angles your sport demands, but well beyond them.

A joint that can only tolerate what running requires has no reserve. The first runner proved that — perfectly adapted to running fast in a straight line, completely unable to function outside that narrow range.

Pattern training loads whatever mobility, control, and capacity you bring to it. Joint and connective tissue training changes those inputs — which is exactly what both runners needed. For the first, that meant restoring hip rotation and extension so the glute could do its job. For the second, it meant building genuine hip abduction strength so the pelvis stopped dropping on every right-side step. In both cases, the ankle needed more usable dorsiflexion so the structures above and below it weren’t constantly compensating.

After that work is done, squatting, hinging, lunging, and jumping hard make sense. Patterns become the test of your joint and connective tissue work, not the treatment for it.

That’s the flip most runners never make. Not because they don’t work hard enough — but because nobody told them the order mattered.

For most runners over 40, joints and connective tissue have been quietly losing capacity for years. The fitness is real. The compensation is impressive. Both have a ceiling — and that ceiling tends to appear exactly when the miles pile up or the tendon runs out of tolerance.

Both of these runners are now working on the foundation.

The question isn’t whether your joints need attention. It’s whether you realize it before the injury — or after.

That’s what I posted to Substack after the session. I meant every word.

The dude can flat out run. But I wasn’t expecting what I found on the table.

Dr. Andreo Spina, founder of Functional Range Systems, says the goal of movement training is simple: “Make shit work nice.” Not a single joint on this man’s body does.

Both hips tight. Quads and hamstrings tight bilaterally. Both ankles limited in dorsiflexion — left worse than right. He could barely touch his shins, let alone his toes — and only by rounding his upper back so aggressively it was doing the work his hips and pelvis couldn’t do. His pelvis was unlevel. His right foot turned out when he walked.

Range was limited. Control was worse.

His all-time best in the mile is 4:23. His marathon PR is 2:14. His 50K best is 3:12.

Built to run. Not built to last.

His body organized itself around one thing

Running fast in a straight line.

The hips don’t need full range if every run is forward motion. The ankles don’t need to dorsiflex if the terrain is flat. The upper back doesn’t need to rotate if the arms are just driving forward. The pelvis doesn’t need to be level if compensation has become the baseline.

Compensation is not failure. Compensation is brilliance. It is the body finding a way to keep producing output despite lost options elsewhere.

But compensation has a ceiling.

This runner came to me after a national championship 100K fell apart between miles 31 and 37. Left adductor and hamstring progressively shutting down in the second half of a race he was otherwise executing perfectly.

The sports hernia years earlier — left side. The hamstring rupture before that — left side. Now this. Three separate injuries, same side, same structural environment expressing itself at different tissue failure points across decades of high-mileage training. Physical therapy addressed the injuries. Nobody addressed the pattern.

He told me the dysfunction is always there. He just runs through it.

Until he can’t.

What the table showed

My lane is movement assessment and strength coaching — evaluating how athletes move, where capacity is missing, and what that means for how they should be training. I’m not a physical therapist or physician. What I found on the table wasn’t a diagnosis. It was a picture of a system that had adapted brilliantly to one demand and abandoned everything else.

The pelvic asymmetry — left ASIS higher and more medial than the right — pointed toward a structural finding that warrants confirmation from a qualified manual therapist. But you don’t need to resolve that question to understand what it was doing downstream. When the pelvis sits asymmetrically, everything attached to it gets forced to solve a different problem: the adductor origin shifts into a chronically compromised position, the glute gets inhibited, the rectus femoris shortens, and the hamstring quietly takes over work it was never designed to do.

He felt it himself during the hip assessment. “The left is harder. My left adductor feels tighter.” He noticed it before I said a word.

The prone knee bend confirmed bilateral quad stiffness. Hip extension confirmed the motor pattern: on the left side, the hamstring fired before the glute. That’s not an injury. It’s a compensation that became permanent.

For ten miles it’s manageable. For twenty, sustainable. For 100K at championship pace, the hamstring accumulates load it was never designed to carry. The adductor, already sitting at its mechanical limit, goes with it.

At mile 31 they shut him down.

When the engine outruns the chassis

Most runners hear a story like this and think: weak glutes, weak hips, needs more strength work. That’s the right diagnosis and the wrong picture of what it means.

The conventional answer is to add strength training. Squats, deadlifts, lunges. Build the posterior chain. Fix the glutes. That’s not wrong — but it’s incomplete. Arbitrary movement patterns don’t address the joints and tissues that make a runner durable. They don’t restore the ranges a hip has stopped expressing. They don’t teach a glute to fire before a hamstring. They don’t build the tissue tolerance an adductor needs to survive 100K.

What this runner needs isn’t to become a powerlifter. He needs his joints to work properly — each one, with access to the ranges his sport demands and the ranges his sport has slowly taken away. That’s an entirely different method and an entirely different way of thinking about strength.

It’s also exactly what FRS is built to do.

This runner has no race on the calendar. He’s not rushing back. What he has is a clear picture of what’s actually wrong and an open window to address it before the next start line.

In Part 3, we’ll get into what that actually requires — why joints and connective tissue are where most runners over 40 are most exposed, and the system I use with my clients and myself to address it.

DNF.

This runner reached out after a national championship 100K fell apart on him. He’d done everything right — the training, the pacing, the fueling — and his body failed him anyway. He wanted to know why.

I had my suspicions.

It’s a pattern I see repeatedly with runners over 40. They do everything right from an endurance standpoint and still end up sidelined. Their aerobic system is prepared.

But their connective tissue isn’t.

That’s the timeline most runners and coaches fail to account for.

Fitness improves faster than durability

Your cardiovascular system adapts quickly. Add mileage consistently and within a few weeks VO2 max improves, lactate threshold shifts, mitochondrial density increases. Muscle responds almost as fast: neural adaptations within two weeks, noticeable strength gains by week four, structural changes following shortly after.

That speed is part of the problem.

Tendons, ligaments, and fascial tissue adapt on a slower timeline. Tendon adaptations show minimal change before two weeks of loading. Meaningful collagen synthesis and stiffness increases require 2–8 weeks of consistent mechanical stress. Peak structural changes — the kind that increase cross-sectional area and mechanical stiffness — take 12 to 14 weeks.

The biology is specific: within four hours of a resistance session, genetic activity shifts in tendon cells. After four days, type I collagen production increases substantially, accompanied by a 35-fold spike in the enzyme responsible for cross-linking newly formed collagen. But collagen content doesn’t equal tendon stiffness. The tissue has to synthesize new protein, organize it along lines of stress, then cross-link it into a mechanically robust structure. That process can’t be rushed. Increases in collagen content precede increases in tendon stiffness by roughly one month.

One study of triathletes following a 12-week heavy slow resistance protocol measured a 39% increase in Achilles tendon stiffness and a 16% increase in patellar tendon stiffness. Not at four weeks. Not at eight. Twelve weeks minimum.

Most runners make training decisions based on how they feel. Muscles, lungs, and motivation all improve faster than the tissues that have to absorb the load.

Two ways runners break down

There are two common ways this mismatch shows up.

The first is a strength mismatch. You add 40 pounds to your squat over eight weeks. Your quads are stronger, glutes fire better, you feel powerful. But tendons adapt to new loading demands over 12–14 weeks. Muscles adapt fast. The tendon is still in process. You ramp up tempo runs and hill repeats because you feel strong. Your muscles can generate the force. Your tendon can't yet absorb it at that volume and intensity. Week nine, you develop patellar tendinopathy.

The second is pure volume. No strength training, no sudden increases in intensity. Just a runner who has been logging big weeks, month after month. Tendons accumulate microdamage with every footstrike. Given enough recovery, they repair. Without it, the damage compounds. By the time he feels it, it’s been building for weeks.

Different pathway. Same root problem.

The connective tissue adaptation timeline was never respected.

The margin narrows after 40

For runners over 40, this matters more. Collagen turnover slows with age. Growth factor responses diminish. Recovery between loading sessions takes longer. The adaptation windows that worked in your 30s are longer now.

Injury history tightens the margin further. Scar tissue from old strains, tears, or surgeries creates areas that don’t lengthen, glide, or absorb load the way healthy tissue does. They may hold fine at 40 miles per week. They fail at 60 miles in a single day.

This runner had a sports hernia and a hamstring rupture, both on the left side, a few years ago. Extensive PT got him functional — strong enough to train, mobile enough to race. But functional isn’t the same as durable. Under sustained championship-level load, those structures couldn’t hold. Not because he was unfit. Because the tissue capacity was never rebuilt to match the demand.

Generic strength training isn’t enough

The solution seems obvious. Start strength training. But that’s only true if the training is built around the tissue timeline, not just the training calendar.

Strength training matters. A large-scale analysis found it reduces overall injury risk by around 30%. Specific protocols do better: Nordic hamstring curls cut hamstring injury risk by 63%. Targeted hip strengthening reduces groin injuries by 31%.

But generic strength training — what most runners actually do — is not the same as tissue-specific capacity work.

A randomized controlled trial of 720 first-time marathoners tested a structured 12-week, three-times-per-week program targeting hip abductors, quads, and core. The intervention group showed no reduction in major overuse injuries compared to controls. Essentially identical injury rates, even among athletes who adhered at least twice a week.

This wasn’t a poorly designed program. It was structured, consistent, and long enough to produce adaptation — and it still failed.

Three reasons it fell short.

No individual assessment. Some athletes need tissue remodeling. Others need motor control work. Everyone in this trial got the same exercises regardless of their actual restriction.

Started too late. Twelve weeks before a marathon doesn’t give connective tissue enough time to adapt when you’re simultaneously ramping mileage.

Wrong loading parameters. Generic strengthening doesn’t drive the collagen synthesis, cross-linking, and stiffness adaptations that reduce tendon and ligament injury risk.

The answer isn’t more strength work. It’s the right loading, applied to the right tissue, early enough for adaptation to actually happen.

If you only follow how fit you feel, you will outrun what your tissues are prepared to handle.

That’s how strong runners still get injured.

In Part 2, we’ll look at how to find the deficits before they become injuries.

This piece goes deeper into those questions—what’s actually changing in your muscle, why running more doesn’t fix it, and what does. It’s longer and more technical than what I usually write here. I’ve tried to make the biology accessible without losing the specificity that makes it actionable. If you want the mechanism, it’s here. If you want to skip to the practical prescription, it’s at the end.

But I’d encourage you to read the whole thing. Most aging athletes who dismiss this topic don’t fully understand what they’re dismissing.

Two kinds of muscle fiber, and why only one really falls apart with age

Human skeletal muscle contains two primary fiber types.

Type I fibers are slow-twitch. They’re oxidative, fatigue-resistant, and built for sustained output. They’re your endurance engine. Every easy run, every long trail, every zone 2 session is primarily a Type I fiber event.

Type II fibers are fast-twitch. They generate high force rapidly. They’re responsible for power, rate of force development, and the capacity to produce explosive contractions. They’re what let you surge on a climb, catch yourself when you clip a rock, or hold your form when everything else is falling apart in the back half of a long race.

Here’s what almost no one in the endurance world talks about: these two fiber types do not age the same way.

A 2025 study in Experimental Physiology recruited healthy, lean, recreationally active men — matched for body mass, BMI, and activity level — at two ages: 22 and 69. No couch potatoes. No frail elderly. Just healthy, active men, half young, half old.

Result:

Type I fiber size in the older group: essentially preserved.

Type II fiber size in the older group: about one-third smaller.

The proportion of Type I fibers shifted from roughly one-third to over half of the total fiber pool. Type II fibers weren’t just smaller — they were more irregular in shape. The proportion of denervated fibers (fibers losing their nerve supply) was markedly higher, and Type I fiber “grouping” had exploded compared to the young men.

The authors’ takeaway was blunt: a normal, recreationally active lifestyle — exercising two to three times per week — is not sufficient to preserve fast-twitch fiber size and innervation in older adults. These weren’t inactive men. They were doing what most “fit” guys do. It wasn’t enough.

I’m watching a version of this in my own training right now. I’ve been rebuilding my trail and mountain running capacity this year after time away. My lungs aren’t the limiter. My legs are. That’s not a basic fitness deficit: my heart and lungs are fine. It’s the factory floor telling me exactly what this research describes.

If you’re a 40+ runner who mostly “does some lifting” with light weights or circuits on the side, there’s a good chance some version of this is happening in your muscle, too.

The neuromuscular junction: where the clock starts ticking

To understand why this happens, you need to understand the neuromuscular junction.

The neuromuscular junction (NMJ) is the synapse where a motor neuron meets a muscle fiber. It’s the electrical interface that makes voluntary movement possible. When your brain sends a signal to contract, that signal travels down a motor neuron and crosses the NMJ to trigger the muscle fiber.

With age, NMJs deteriorate — and they deteriorate preferentially in fast-twitch fibers. The structural and functional degradation at Type II fiber NMJs is more severe and begins earlier than at Type I fiber NMJs. This isn’t a footnote. It’s the upstream cause of a cascade of remodeling in aging muscle.

Here’s the sequence.

Motor neurons begin withdrawing their connections from fast-twitch fibers. Once a fiber loses its innervation, it begins to atrophy. A compensatory mechanism called reinnervation attempts to rescue it: adjacent motor neurons — often slow-twitch units — sprout new branches and reconnect to the denervated fiber.

When reinnervation succeeds, the rescued fiber takes on the characteristics of the new motor neuron. A fast-twitch fiber converts toward a slow-twitch phenotype. Over time, more fibers get converted, and motor units become larger groupings of similar fiber types.

This is why older muscle shows more Type I fibers and fewer Type II. The conversion is happening constantly, driven by chronic, low-level denervation and reinnervation.

For years, this cycle compensates surprisingly well. Muscle strength and function can look acceptable on the surface while the underlying wiring is being rewired and pruned.

But the compensatory capacity doesn’t hold forever. At some point, denervated fibers that can’t be successfully reinnervated become apoptotic — programmed for cell death. They are not replaced with new, functional fibers. What started as a gradual conversion becomes an outright loss of muscle fibers and motor units.

Longitudinal neuromuscular aging studies show that these processes, with fewer but larger surviving motor units, start as early as 50-60 and accelerate in adults over 70-75. Other work shows a fast decline in alpha motor neuron cell bodies in the spinal cord beyond 60, along with a parallel decline in motor unit numbers.

If you’re in your 40s or early 50s, this isn’t a distant future event. The remodeling has likely already started — it just hasn’t hit the point where everything feels like it’s suddenly falling off a cliff.

Mitochondria make this worse. They are clustered on both sides of the neuromuscular junction, which may increase NMJ vulnerability to age-related mitochondrial dysfunction. As mitochondrial respiratory capacity declines, ATP production falls, oxidative damage accumulates, and apoptotic signaling increases — all of which can further undermine NMJ stability.

Large cohort work in older adults has found that greater muscle fiber disorganization is associated with lower VO₂peak, lower leg power, and reduced mitochondrial oxidative phosphorylation, even after controlling for muscle volume. The data is correlational, but the structural deterioration and the functional decline appear to be connected at the cellular level.

Why your mileage doesn’t fix this

This is the part that matters most if you’re reading this as a 40+ endurance athlete.

A recent study in the Journal of Applied Physiology compared four groups, all with actual muscle biopsies: young recreationally active adults around 25, lifelong strength-trained master athletes around 73, lifelong endurance-trained master athletes around 72, and recreationally active older controls around 75.

The endurance masters had significantly higher relative VO₂max than the strength masters — about 47 vs. 33 mL/kg/min. Their aerobic engine was clearly superior. Decades of systematic endurance training had done exactly what endurance training is supposed to do.

Their muscle fiber profiles looked very similar to the recreationally active older adults.

On key measures — Type II fiber distribution, fiber type grouping, atrophic fiber content — the endurance masters and the older controls were statistically hard to distinguish. Both groups showed reduced Type II representation and signs of remodeling and denervation. The authors were blunt: neither general physical activity nor high levels of long-term endurance training appears sufficient, by itself, to maintain Type II fiber properties and innervation with aging. The specific loading pattern matters more than the sheer volume of training.

This is not a failure of endurance training. It’s a description of what endurance training does.

Endurance work is sustained, moderate-force, high-repetition, and mostly low to moderate intensity at the muscle level. It’s extremely effective at developing slow-twitch oxidative capacity and the cardiovascular system. But the quality aging attacks most aggressively — the capacity to generate high contractile force quickly from fast-twitch fibers — is not what endurance training is built to train.

A nuance for trail runners and obstacle racers

Technical trail running, obstacle racing, weighted carries, steep descents — these are not neuromuscularly passive activities. Compared to flat road running, they recruit more muscle mass, demand more stabilization, and use more fast-twitch fibers, at least intermittently. That’s a big part of why trail and mountain runners often stay more “durable” than pure road runners.

But even demanding trail running is still dominated by sustained, moderate-force, high-repetition contractions over long durations. What erodes fastest with age is peak force production and the capacity to generate high force quickly. Hills and technical descents help more than flat mileage, but they still do not replicate what heavy compound loading does to Type II fibers and their motor neurons. Think of them as complementary tools, not interchangeable ones.

If your training is 90% endurance with a bit of light strength work tacked on, you’re developing the systems that age least, and neglecting the system that age strips away first.

What heavy loading does that nothing else quite matches

Here’s why loading intensity matters so much.

At the neuromuscular junction level, high-intensity mechanical loading triggers structural adaptations that low-load contractions simply don’t generate. The signal that stabilizes NMJ architecture requires heavy loading to fire. Bands and bodyweight circuits may help maintain what you currently have, but they are unlikely to rescue fast-twitch fibers already being abandoned by their motor neurons.

At the fiber level, the evidence is just as specific. A meta-analysis of strength training in older adults found no measurable strength improvements below about 50% of one-rep max. In one study, 100 bodyweight squats per day for four months did not increase maximal strength in older adults because the intensity was too low relative to their capacity. Volume and intensity are not interchangeable.

What heavy loading at 80-90% of 1RM produces in older adults: preferential Type II fiber hypertrophy, improvements in maximal strength and rate of force development, and neural adaptations — greater motor unit recruitment and firing rates — that don’t appear to the same degree with light loads.

Biopsy data shows that very heavy strength training in older adults can increase Type II fiber area and distribution — moving the needle back toward a younger muscle profile.

Even more striking: lifelong strength-trained master athletes showed muscle fiber type distribution and grouping patterns similar to young, moderately active adults. The denervation markers that characterized every other older adult group were largely absent.

The most likely explanation: decades of regularly forcing the nervous system to recruit high-threshold, fast motor units under heavy load helps preserve their innervation and function.

There’s also a motor neuron maintenance mechanism worth spelling out. The descending neural drive — from motor cortex to spinal motor neurons to muscle fibers — declines with age. Heavy strength training produces large increases in this signal. Recreational activity doesn’t, because it never fully recruits the fast motor units that need the stimulus. Occasionally picking up something truly heavy sends a “keep this system online” message to your nervous system in a way that jogging and circuits don’t.

Safety, intensity, and what the guidelines miss for aging runners

Current guidelines for older adults often recommend 60-70% 1RM for strength training. That’s a reasonable starting point. But three decades of research suggest that heavier loading — 80-90% 1RM — has unique benefits for preserving fast-twitch fibers and neuromuscular function once technique and tolerance are in place.

The evidence base for heavy loading in older and even clinical populations is now substantial. Studies have implemented it safely in healthy adults in their 60s, 70s, and beyond; nursing home residents in their 80s; hip fracture patients; stroke survivors; osteoporosis patients; and cancer patients undergoing therapy.

In these trials, heavy loading was introduced from the first sessions, with careful coaching and progression. The key isn’t avoiding heavy loads forever.

The key is how you get there.

Risk of injury comes primarily from uncontrolled eccentric loading (the lowering phase), poor technique, and inappropriate jumps in load — not from the concentric force production itself. Protocols that have been used safely across these populations share a pattern:

• Slow, controlled eccentrics (2-3 seconds)

• Brief pause in the bottom position

• Explosive concentric intent (trying to move the weight fast), even though the bar itself moves slowly because the load is heavy

• Most sets should stop with 1–3 reps in reserve, not to true failure

Two additional findings are directly relevant for the endurance athlete.

Heavy, low-rep strength training usually produces a lower overall cardiovascular load than higher-rep, moderate-load training — making it the safer end of the strength spectrum for athletes with any cardiac concerns.

And heavy strength training reduces the oxygen cost of locomotion. Running economy improves following maximal strength training across multiple populations. It’s not in competition with your running. It makes your running more efficient.

The take-home: once you’ve built basic technique and tolerance, staying permanently in the 15-rep, “toning” zone is a missed opportunity. Heavier work — done well — is both safe and specifically targeted at the system aging is degrading.

The practical prescription for a 40+ athlete

You don’t need a powerlifter’s schedule to get the benefit. You need a focused, repeatable protocol.

Core principles:

• 2-3 sessions per week

• Built around compound lower-body movements: horizontal leg press, squat variation (back, front, safety bar, or goblet depending on your level), deadlift variation (trap bar is often friendlier), single-leg work (split squat, step-up, RDL variations)

• Some plyometric or power-oriented work once you have a base (jumps, bounds, medicine ball throws)

• Most sets stopped with 1-3 reps in reserve

• Strength sessions separated from hard run sessions by several hours when possible

Off-season: build maximum strength

Goal: raise your ceiling — maximum force and Type II recruitment.

• 2-3 sessions per week

• 3-4 compound exercises per session

• 4 sets of 4-6 reps at roughly 80-90% of 1RM on the main lifts

• 3-4 minutes rest between sets

• Tempo: slow controlled eccentric (2-3 seconds), brief pause, then concentric with maximal intent to move fast

• Progression: once you can complete 5-6 quality reps for all sets at a given load, add weight next time

If you’re newer to lifting or coming back from injury, start closer to 60-70% 1RM, learn the movements, and work up over a few months. The destination, not the starting point, is the heavy loading zone.

In-season: maintain the neuromuscular signal

Goal: keep fast motor units recruited and innervated with minimal fatigue cost.

• 2 sessions per week

• 2-3 sets of 6-8 reps at about 60-75% 1RM on key lifts

• Focus on bar speed: move with maximal intended velocity while maintaining solid technique

• Velocity mindset: stop the set when rep speed noticeably drops, even if you have reps left

You are not trying to add weight to the bar in race season. You’re trying to remind your nervous system, twice a week, that those high-threshold units are still required. You cannot replace this signal with bodyweight circuits and get the same effect. You can, however, keep the volume low enough that it doesn’t trash your legs for key run sessions.

A seven-month study of elite soccer players — athletes with very high concurrent aerobic and strength volumes — found that a power-oriented resistance protocol not only maintained but improved relative power and strength across the season. The neuromuscular gains were gradual and not obvious week to week, but they accumulated. The athlete “not feeling it doing anything” was still adapting. That’s exactly the pattern you should expect.

The window — and why this matters more than your next PR

The denervation-reinnervation cycle is remarkably effective for a long time. The losses are gradual, and for years the compensatory mechanism keeps pace. This is why most athletes don’t notice anything until they suddenly notice everything — a plateau that doesn’t respond to more mileage, a back half of long efforts that keeps getting slower, recovery that feels a little worse every season.

But the compensatory mechanism does eventually fall behind. And once motor neurons die back and fibers go apoptotic, you’re not regrowing that tissue in any meaningful way. You’re managing around its absence.

NMJ reinnervation becomes increasingly difficult once denervation is established. Alpha motor neuron losses accelerate after about 60. The window to get ahead of this — to maintain the heavy, high-threshold stimulus that keeps fast motor units recruited and their NMJ connections intact — is widest in your 40s and early 50s.

If you’re past that window — 60, 70, or beyond — it is still absolutely worth lifting heavy in a way that’s appropriately scaled. The goal shifts: you’re fighting to slow losses and raise function above the “expected” curve, rather than simply protecting what’s already there. But that fight is still worth fighting.

This is not just a performance argument. It’s a longevity and quality-of-life argument.

The fitness you build on top of a deteriorating neuromuscular infrastructure is fragile. The fitness you build on a maintained infrastructure compounds. The difference shows up not just in your race photos next year, but in your ability to get off the ground quickly and confidently in your 70s.

In that earlier piece I said: you can rebuild fitness; you can’t rebuild the decade you spent letting the infrastructure erode.

Everything I’ve read since has reinforced that idea.

The athletes who figure this out aren’t just stronger this season.

They’re still athletes next decade.

If this piece raised questions about your own training — what you’re currently doing, what might be missing, or how to build a program that addresses this — I’m happy to talk. Reply to this email or leave a comment below. That’s what this is for.

Next week: why joints and connective tissue may be the most neglected layer in the durability conversation — and what training actually addresses it.

It’s not whether you can get faster. It’s whether you’ll still be able to do this at 55. At 60. Whether the body that’s been carrying you through races and training blocks for twenty years will keep cooperating — or whether you’ll slowly become someone who used to run.

That’s the question most endurance athletes are quietly carrying. And it’s the question the strength training debate, for all its rigor, has almost completely failed to answer.

A few months ago I left a comment on a Niki Micallef article at Born on the Trail. His piece was titled “Why Runners Should Not Strength Train” — a deliberately provocative headline for what turned out to be a genuinely rigorous argument. My comment pushed back slightly, suggesting that strength training for runners is less about chasing the final 2-3% of performance and more about protecting the ability to keep accumulating the stimulus that matters most: mileage.

Niki agreed more than he disagreed. He responded at length, clarified what his argument was and wasn’t saying, and then told me publicly, in his own comment section, that I should write the article making the case for resistance training.

So here it is.

I want to be clear about something before I make this argument. Niki and I aren’t really in disagreement. His central premise — that running performance is primarily driven by running — is correct. I’m not here to dispute it.

What I want to do is answer the question his framework wasn’t designed to address. His piece is about optimizing a season. I’m interested in protecting a decade. Those aren’t the same question, and they don’t have the same answer.

The question Niki is answering: Will strength training make me faster?

The question I’m interested in: Will I still have the fitness to run hard at 55? At 60?

And the research that answers the second one points somewhere the performance literature hasn’t been looking.

Your aerobic ceiling has a floor

Here’s what most endurance athletes — and most of the strength training debate — miss.

VO₂max is typically framed as a cardiovascular number. How well your heart pumps blood, how efficiently your lungs oxygenate it, how effectively your muscles extract oxygen from it. Cardio improves it. Lifting doesn’t. That’s the conventional model.

But the conventional model is incomplete.

Your heart and lungs are the supply side of the system. They deliver oxygen to your muscles. Your muscles are the demand side — they’re what actually consume that oxygen and convert it into movement. And here’s the part that changes the conversation: if your muscles can’t generate enough power, your cardiovascular system never gets asked to work at its ceiling. There’s no demand pulling it there.

Think of it as a factory. Your cardiovascular system is the supply chain — capable of delivering a thousand units a day. But if the factory floor can only process two hundred units, those delivery trucks are mostly parked. The supply chain’s capacity is irrelevant because the demand never shows up.

Your muscles are the factory floor.

Researchers at Harbor-UCLA Medical Center, using a modified exercise test called the musculo-cardiopulmonary exercise test (mCPET), have been measuring this relationship directly. By testing peak isokinetic cycling power — the maximum force the legs can apply at a fixed cadence — alongside standard VO₂max measurement in the same test session, they found something that should reframe how we think about aerobic decline.

Peak neuromuscular power correlates strongly with VO₂max. When researchers normalized VO₂max to isokinetic muscle power rather than body mass or lean mass, the age-related gap in aerobic capacity essentially disappeared. I’ll be honest: this research is still early — one lab group, small samples, some animal model data. But the mechanism is physiologically coherent, and the uncertainty cuts in a specific direction.

The apparent aerobic decline with aging isn’t primarily a story about failing hearts and lungs. It’s substantially a story about weakening muscles that can no longer generate the demand that drives the aerobic system to its ceiling.

The aging problem

Niki’s argument is built almost entirely around performance optimization — what makes you faster, what predicts ultramarathon success, what the highest-return intervention is for a competitive runner. The Knechtle data, the Casado data, the Koop hierarchy — all of it is oriented toward the performance question. That’s legitimate. That’s his audience.

But there’s a biological reality the performance conversation tends to ignore.

As we age, muscle mass, force production, and aerobic capacity tend to fall together. They’re connected systems, not separate ones — driven by overlapping biology centered on mitochondrial dysfunction and neuromuscular junction degradation. The losses are modest in early older age, then accelerate sharply. The implication is uncomfortable: you cannot fully protect your aerobic ceiling through endurance training alone if the neuromuscular substrate underneath it is eroding. More running develops the supply side. It does relatively little for the factory floor.

This is not a small caveat. This is the central issue for anyone over 40 who intends to still be running hard at 60.

A fair objection

There’s one version of the counterargument I take seriously.

Trail running, hill running, obstacle racing — these are not neuromuscularly passive activities. Downhill eccentric loading, steep climbs, carrying awkward weight over uneven terrain — athletes doing this kind of work are generating significant neuromuscular demand through the sport itself. The argument that endurance training neglects the factory floor is more defensible for someone running flat roads than for someone descending four thousand feet in a Spartan Beast.

I don’t dismiss that. If you’re regularly running technical trails, doing heavy carries, and grinding out long descents, you’re getting a neuromuscular stimulus that a road marathoner isn’t.

But here’s the distinction worth holding onto. The neuromuscular stimulus from running — even demanding trail running — is primarily endurance-oriented. Sustained, moderate-force, high-repetition contractions over long durations. What erodes fastest with age isn’t that quality. It’s fast-twitch fiber recruitment, peak force production, and the capacity to generate high force quickly. Trail running preserves some of that better than road running. It doesn’t replicate what heavy compound loading provides. The quality your sport helps maintain and the quality aging attacks most aggressively are not quite the same thing.

What the research actually shows

In 2024, researchers proposed that endurance performance has a fourth determinant beyond the three variables in the classical model — one they called physiological resilience (or durability, as I've been calling it here): the ability to resist fatigue and maintain performance as exercise proceeds. The striking finding from the research they reviewed wasn’t just that resilience matters — it’s that baseline fitness doesn’t predict it. Critical power can fall anywhere from less than 1% to 32% after two hours of heavy exercise in different athletes with nearly identical starting values. VO₂max, lactate threshold, running economy measured fresh — none of them tell you how someone will hold together in the back half of a long race. They named strength and plyometric training as a candidate intervention for improving resilience, and noted the question remained open.

It has since been answered.

A 2025 randomized controlled trial out of Loughborough University, conducted at marathon-equivalent intensity, found that ten weeks of strength and plyometric training improved running economy durability and increased time to exhaustion after a 90-minute run by 35%. The endurance-only control group showed no improvement. Fresh-state running economy didn’t change in either group, which is consistent with what Niki found in the performance literature.

The argument was never about what happens at the start line.

Two different questions, two different athletes

Niki is writing for a competitive trail runner who wants to optimize performance next season. His advice for that athlete is sound: if you’re under 10 hours a week, run more before you lift more. The opportunity cost argument holds.

But that’s not who reads this newsletter.

The athlete I’m writing for has been running for twenty years. He’s not under 10 hours a week because he lacks the base — he’s under 10 hours a week because he has a job, a family, and two knees that need managing. He's not asking whether lifting will take 30 seconds off his 10km time. He's asking whether it will keep him running at 60.

For that athlete, the neuromuscular floor under the aerobic ceiling is the right thing to be thinking about. Not because strength training replaces running — it doesn’t, running is still the primary stimulus — but because maintaining the muscular capacity that keeps the aerobic system operating at a high level is not optional. It’s the infrastructure that everything else runs on.

The debate about whether runners should lift has been fought almost entirely on performance grounds. More running vs. lifting for race times. Economy improvements vs. volume accumulation. That’s a useful debate for a specific athlete at a specific stage.

It misses the longer game entirely.

What this looks like in practice

The concurrent training research is specific about what works. Two to three resistance sessions per week, focused on compound lower body movements — squats, deadlifts, single-leg work — with some plyometric loading. Separated from hard running sessions by several hours. Not taken to failure. Not to the point where it compromises the quality of the next run.

That’s not a major time commitment. And it’s not in competition with your running. It’s protecting the system that makes your running possible — not just next season, but for the decade after that.

Niki ended his follow-up piece with the same ACSM Position Stand I’ve been referencing here — and arrived at a conclusion that’s closer to mine than his headline suggested. For athletes who have surpassed the volume threshold, for those frequently sidelined by injury, or for those specifically optimizing for long-term health and longevity, resistance training becomes an important addition.

That’s his reader at one stage of the journey.

My reader is further down the road. He’s been running for twenty years. He’s not debating whether to prioritize volume or lifting this season — he’s trying to figure out how to still be doing this in ten years. He’s asking a question that the performance literature, for all its rigor, wasn’t built to answer.

For that athlete, the argument isn’t about opportunity cost. It’s about what happens to your aerobic ceiling when the neuromuscular floor underneath it quietly gives way — and whether you addressed it before it was too late to matter.

Niki is right that the factory floor isn’t where most runners should start. But at some point — and for most of the men reading this, that point is now — it becomes the thing most worth protecting.

Because you can rebuild fitness. You can’t rebuild the decade you spent letting the infrastructure erode.

The athletes who figure that out aren’t just stronger this season.

They’re still athletes next decade.

If this landed, forward it to the runner in your life who keeps saying he’ll start lifting after his next race. He’s been saying it for years.

If you're an athlete over 40 and your body keeps breaking down in the same places, this checklist will show you exactly why. It covers five areas where most older athletes have gaps they don't know about. Download it, work through it honestly, and you'll know where your system is failing within five minutes.

Download your free Train Hard After 40 Diagnostic Checklist here

Which section has the most checks for you? Reply and let me know.

My heart rate wouldn’t cooperate. The plan was to run — 6.0 mph at 3% incline. But to stay under 135 bpm — my aerobic ceiling for this section of the workout — I had to drop the speed to 4.5 and pull the incline back to 2%. Not because my lungs gave out. Not because my aerobic system was failing. Because after having already performed an hour and fifteen minutes of incline work — capped by 30 minutes of power hiking at 3.0 mph and 10% grade — my hips and posterior chain were cooked. That local muscular fatigue was driving my oxygen demand up enough that running at the prescribed pace pushed me out of the aerobic zone entirely.

I knew exactly why it happened. I haven’t been consistent with my lower body strength training.

I’ve been consistent with everything else — long aerobic sessions, sled work, daily mobility. But the sled work, while valuable for uphill force production, is primarily concentric loading. Low eccentric stress, which is great for my knees, doesn’t build the musculotendinous stiffness that protects running economy when fatigue accumulates. And while my mobility work has genuine value for joint capacity and tissue quality, it isn’t a substitute for the heavy loading that drives the neural and structural adaptations strength training produces.

Weeks without heavy loading. The hips noticed.

The HR trace from this morning. The spike between 1:40 and 1:45 is what happened when I tried to run after an hour and forty minutes of incline work — including 30 minutes of power hiking at 10% grade. The legs quit before the lungs did.

The gap in the durability conversation

Durability — the ability to maintain performance as fatigue accumulates — has gotten real traction in endurance circles lately. The concept is legitimate and important. But the conversation around it is almost entirely aerobic. Zone 2 volume. Cardiac drift. Fatigue resistance built through chronic endurance work.

Everyone’s building the engine. Nobody’s checking the chassis.

What the research shows

A 2025 randomized controlled trial from Loughborough University tested this directly. Well-trained male runners were split into two groups: endurance training only, and endurance plus twice-weekly strength training for ten weeks. Both groups ran the same volume. After the intervention, both groups ran for 90 minutes at marathon-race intensity, then immediately ran to exhaustion at near-maximal speed.

The endurance-only group’s running economy deteriorated 4.7% over the 90-minute run. The strength group’s deteriorated 2.1% — less than half. Then came the number that should stop every endurance athlete cold: time to exhaustion improved 35% in the strength group. The endurance-only group got slightly worse.

This is the finding the mainstream durability conversation is missing. Strength training didn’t improve VO2max. It didn’t raise lactate threshold. What it did was slow the mechanical breakdown that makes the second half of a long race progressively more expensive.

The mechanism is straightforward. Stronger muscles require a smaller fraction of their maximum force output per stride. That delays fast-twitch fiber recruitment — which means less lactate, less efficiency loss, less drift. It also increases musculotendinous stiffness, returning more energy from each ground contact instead of absorbing it as waste. Economy holds.

What this morning actually showed

My aerobic system is adapting well. In the week since my last long session, average heart rate dropped from 132 to 129 bpm while total time increased 33% (from 1h 45m to 2h 20m) and Zone 1 and 2 time jumped from 55% to 72%. The engine is building.

But the legs let me down exactly where Utah will test them most — transitioning from a long climb into a run. And I can trace it directly to weeks without consistent heavy loading. Mobility has genuine value for joint capacity and tissue quality — I’ll make that case in a future article. But it doesn’t replace the neural and structural adaptations that come from loading tissue under tension. The hips and posterior chain that failed this morning need more range of motion, yes. But they also need to be stronger.

That’s where most endurance athletes get it wrong. The aerobic side gets meticulous attention. Strength work gets treated as optional — something for the off-season, something that competes with training rather than enabling it.

The research says otherwise. Two sessions per week. Heavy lower body loading, kept simple and consistent. To be clear, the evidence isn’t perfect and one session proves nothing on its own. This was supposed to be a durability test — the aerobic system never came close to its limit. But it exposed something more useful: exactly where the real limit is.

Strength goes back in this week. Not to set records in the weight room. To make sure the legs hold when the climbing stops and the running starts.

12 weeks out.

If you're an endurance athlete over 40 and strength work keeps falling off your schedule, reply and tell me why. I read every response.

Slow down… or suffer through?

By this point the inclined walk had turned into a power hike. Hands on thighs. My breathing was still under control. I could still hear my music.

I just couldn’t sing along anymore.

If I had to rate that section—and I did—it was a 6 out of 10. Not too hard. Definitely not easy. Just work.

Here’s what caught my attention:

Going purely by feel, I ended up moving much faster than the week before when I kept a heart‑rate cap. By the end of the session I’d gone farther and climbed 15% more vertical.

I’d also nearly doubled the training load.

Same perceived effort. Completely different cost.

That gap is what this article is about.

The Questions That Actually Matter

Spend any time in endurance circles and you’ll hear the same advice:

Stay in Zone 2. Watch your heart rate. Don’t let it drift.

It’s become the gold standard for aging athletes—and to be fair, it works. Keeping your heart rate controlled builds your aerobic engine, improves efficiency, and lets you stack training without constantly digging a hole you can’t climb out of.

But there’s a problem.

Most athletes aren’t training for a heart rate number. They’re training for an outcome.

A race.
A finish line.
The ability to go long, go hard, and still hold it together when everything starts to fall apart.

That’s where the conversation breaks down.

On one side: train by heart rate. Control the effort. Stay disciplined. Walk if you have to. Build the base.

On the other: train by feel. Listen to your body. Push when it’s there. Back off when it’s not.

Both sides are right. Both sides are missing something.

Because neither one is really asking the questions that matter most:

What are you getting from this workout?
What is this effort actually costing you?

Not what it feels like.
Not what your watch says.

But what it takes out of you—and what you get in return.

That’s what I wanted to find out.

The Experiment

I’ve always leaned toward training by feel. So I decided to test it.

I repeated the same workout two Sundays in a row.

Same treadmill. Same structure. Same goal: prepare for the Spartan Beast in Utah—a long, grinding, mountain race where the real problem isn’t how fast you go early. It’s what happens after 90 minutes when your legs start to fade and the cost starts to compound.

The only variable: how I controlled the effort.

Week 1 — Heart Rate

I kept things tight. Heart rate as my governor, staying in my Zone 2 / VT1 range, keeping a lid on the effort. Honestly? It felt too easy. Like I was holding back the whole time — which, for me, is exactly the point. I’m notorious for going too hard too early. The HR cap isn’t a suggestion. It’s the only thing that keeps me honest.

The goal was simple: build the engine, control the cost.

Week 2 — RPE

No cap. No guardrails. Just effort.

I used RPE to guide the entire session—letting pace float based on how I felt, pushing when it felt right, backing off when it didn’t. Same structure. Same blocks. But instead of asking what does my heart rate say, I was asking what can I handle right now.

I didn’t expect a dramatic difference. Maybe the RPE day would drift a little higher. Maybe the HR day would be a little more controlled. But I figured they’d land in the same neighborhood.

I was wrong.

What the Numbers Actually Showed

By design, the sessions were nearly identical: same grades, same duration. Perceived effort ended up being the same, too—both sessions averaged a 4 out of 10. Somewhat hard. Controlled. Repeatable.

But when I looked under the hood, the story changed completely.

The output: The RPE session produced more work across the board. I moved faster in key sections, covered more distance, and climbed 15% more vertical. And none of it felt harder.

The cost: Higher average heart rate. Higher peak heart rate. Significantly more time in the upper zones. And then the number that stopped me cold:

Training load: 148 vs 83.

That’s not noise. That’s nearly double. That’s my body saying: this is going to take a lot more to recover from.

The capacity:

Garmin tracks something called Stamina—a running estimate of how much energy you have left as a session progresses. Think of it as a gauge for how much of your system you’ve burned through.

Here’s what it showed:

• Week 1 (HR-guided): 97% → 81% — a drop of 16 points

• Week 2 (RPE-guided): 100% → 71% — a drop of 29 points

Same perceived effort. Nearly double the drop in available capacity.

If you only looked at Session RPE, you’d call these the same workout. If you only looked at output, you’d say the second one was better. But when you factor in cost—and what was left in the tank afterward—the picture gets a lot more complicated.

The Part That Changes Everything

For a 25-year-old, that cost might be manageable. Recover hard, go again a day or two later.

For those of us north of 40, that changes. Recovery is no longer a 48-hour footnote. It’s a variable that determines whether next week’s training happens at all. Dig too deep too often and you’re not building fitness — you’re just accumulating fatigue and wondering why your performance has plateaued. Or why you got injured.

Here’s what I noticed in the hours after the RPE-guided workout: my legs were significantly more tired and sore than they were at this point after the HR-guided session. Not destroyed. Not injured. Just noticeably heavier — the kind of fatigue that confirms the data wasn’t lying about the cost.

The good news? My knees feel fine.

For an athlete with a history of ACL tears and a knee that used to swell after long runs, that matters. The muscular system absorbed the work and is telling me about it. The joints held. That’s exactly the response I want — soreness in the right places, silence in the wrong ones.

That’s durability. And after 40, that’s the whole game.

How to Actually Use This

Stop picking sides. Use both—but use them for different jobs.

Use RPE to drive the session. Push when it’s there, back off when it’s not. Feel is a real, integrated, multi-system signal. Trust it.

Use heart rate to audit the cost. Watch for drift. Watch for accumulation. If your heart rate is climbing while your effort stays flat, something is happening that RPE isn’t catching.

Match the tool to the goal:

Building base? Control the cost. Heart rate is your governor.

Expanding capacity? Push the output. RPE is your guide.

Race prep? Practice managing both at the same time, because that's exactly what race day demands.

The simple version: some days you control the cost. Other days you raise the ceiling. The athletes who last—and keep improving past 40—are the ones who know which day is which.

When you can hear the music but can’t sing along — that’s your body talking. Learn to listen.

Trail races, Spartan races, road races. It didn’t matter. I always tried to get near the front early. I didn’t want to get stuck in packs, and I didn’t want to assume other racers were going to fade. So I pushed the pace early and tried to put myself in position.

The first mile almost always felt great. Smooth, relaxed, controlled. I would settle into a pace and think the race was going to go well.

Then somewhere around miles four through six, everything started to fall apart.

The pace drifted. Hills turned into hikes. Running turned into jogging, jogging turned into walking. Obstacles felt harder. My legs felt heavy. I went from racing to surviving.

And almost every time, the same thing happened. The people I passed early started passing me back.

For a long time, I thought the problem was fitness. I thought I needed a bigger engine. More mileage. Harder intervals. Higher VO₂max.

So I kept trying to get faster.

The Misconception About Endurance

Most endurance athletes think performance is mostly about fitness. VO₂max, threshold pace, mileage, intervals, heart rate zones, running economy. Those things matter. They determine how fast you can go when you are fresh.

But endurance races are not run when you are fresh. They are run when fatigue is already building.

Endurance performance depends on how much of your ability you still have after an hour, two hours, or the second day of a race weekend. Two athletes can test the same in a lab, but if one athlete’s mechanics fall apart after an hour while the other athlete still moves well, they are not equal endurance athletes.

The difference is durability.

A simple way to think about endurance performance is this:

Performance = Maximum Ability − Fatigue

The athlete who can maintain the highest percentage of their ability for the longest time usually wins. Races are rarely won by the athlete who is fastest at the beginning. They are won by the athlete who slows down the least.

What Happens When Fatigue Builds

Most people assume they slow down in long races because their heart and lungs can’t keep up. In many endurance events, that is not the main limiter.

After about 60 to 90 minutes of continuous work, movement starts to change. Running economy gets worse. Stride length shortens. Ground contact time increases. Force production drops. Muscle damage accumulates, especially from downhills. Posture starts to collapse. Grip strength drops. Fuel stores decline and body temperature rises.

The engine may still be capable of producing power, but the body becomes less efficient with every mile.

Durability is the ability to resist that decline and keep moving well when fatigue builds.

Changing How I Train

After taking a year away from racing, I came back with a different focus. Instead of just trying to get fitter and faster, I started focusing on durability and variable pace running.

My intervals are now hard and easy instead of hard and stop. I keep moving during recovery instead of standing still. That forces my body to recover while still moving, which is what races actually require.

I also do more training when fatigued. Running after strength training. Carrying weight after long efforts. Back-to-back hard days. Long sessions where the goal is not pace but staying functional late in the workout.

I manage downhill running more carefully now. Downhills create a lot of eccentric muscle damage and joint stress. If you cannot handle that damage, the rest of the race becomes survival. So I build eccentric strength gradually instead of destroying my legs early in the season.

Strength training has probably improved my durability more than anything else. If every stride requires a smaller percentage of your maximum strength, you fatigue more slowly. Stronger muscles and stiffer tendons help maintain mechanics when you are tired and protect your legs on descents.

I am also training my Spartan athletes this way. One athlete is preparing for a Trifecta weekend, all three Spartan distances over two days. We are not focusing on pace. The goal is to still be functional on the second day.

Most endurance athletes train for the first half of the race. We train for the last half.

The Lesson

Looking back at my racing history, my best performances did not come from getting dramatically faster. They came from building strength, distributing effort better, and slowing down less, whether or not I knew it at the time.

Armed with this knowledge, durability has now become my focus. I still want to get fitter and faster, but I care more about what happens an hour into a race than what happens in the first mile. I care more about how well I can move when I’m tired than how fast I can move when I’m fresh. I care more about finishing strong than starting fast.

That has changed how I train and how I coach. More strength work. More variable pace running. More training when fatigued. More focus on pacing and effort distribution. The goal is no longer just to build a bigger engine. The goal is to build an athlete that doesn’t fall apart when the race really starts.

If you want to perform well in endurance sports, durability matters. If you want to compete for a long time, durability matters even more.

The goal is not just to win races this year.
The goal is to still be racing years from now.