Running Durability: Why You Fade Late in Races and How to Improve It

We spend a lot of time in endurance sports talking about VO₂ max, lactate threshold, and running economy.

And rightly so.

These are some of the key physiological qualities underpinning endurance performance.

But there’s another concept that’s rapidly gaining attention in endurance physiology and marathon performance circles: Durability.

Now, while the term may sound new, the concept itself isn’t. Coaches and athletes have probably observed it for decades, even if they didn’t have a name for it.

Because we’ve all seen it.

Two runners can look very similar early in a race. Similar pace. Similar physiology. Similar training history.

But by 30km, one athlete is still moving efficiently while the other is completely falling apart.

That’s where durability starts to show up.

So What Actually Is Durability?

At its simplest, durability refers to your ability to resist fatigue over time.

Or more specifically:

• How well you maintain physiology and performance as fatigue accumulates.

Because one of the biggest misconceptions in endurance sport is assuming the physiology you start a race with is the same physiology you finish with.

It’s not.

As prolonged exercise continues, several physiological changes begin to occur:

• Running economy can worsen

• Lactate threshold can drift downward

• VO₂ max can decline

• Neuromuscular fatigue builds

• The energy cost of maintaining pace increases

And importantly, this can all happen even if the pace stays the same.

That’s a really important point.

A pace that felt sustainable early in a marathon may become progressively more physiologically demanding later in the race, despite not speeding up at all.

Why This Matters for Marathon Performance

Marathon performance isn’t just about how fit you are fresh.

It’s about how much of that fitness you can preserve once fatigue builds.

This is where durability may become one of the missing links in understanding endurance performance.

Because two athletes with very similar “fresh-state” physiology can respond very differently once they accumulate significant fatigue.

Recent work from Michele Zanini and colleagues has shown that prolonged running can progressively worsen running economy and physiological thresholds. Importantly, the athletes who resist these deteriorations best appear to perform better over long distances.

In other words, the runner who slows the least physiologically often performs best in practice.

Running Economy and Durability

One of the major areas durability research has focused on is running economy.

Running economy is essentially the energy cost of running at a given speed.

More economical runners use less oxygen and less energy to maintain pace.

But here’s the important part: Running economy is not necessarily stable over prolonged exercise.

As fatigue accumulates:

• muscle recruitment changes

• stiffness characteristics may alter

• movement efficiency declines

• energy cost rises

Meaning your body gradually becomes more “expensive” to run.

And if your running economy deteriorates significantly late in races, fatigue accelerates quickly.

This is one reason some runners seem to suddenly unravel despite pacing appropriately early.

Are Long Runs Part of the Answer?

Potentially yes.

One of the more interesting findings from recent research is that runners regularly performing longer runs appear to show better running economy durability.

In one study, runners accustomed to regular long runs demonstrated:

• better preservation of running economy

• smaller decrements in strength and power

• less physiological deterioration during prolonged exercise

Importantly, these runners were matched for performance.

That suggests durability may not simply be about talent or fitness, but also how you train.

This makes intuitive sense.

Long runs may not just build aerobic fitness. They may also expose the body to prolonged fatigue states and improve your ability to maintain efficiency as fatigue accumulates.

What About Strength Training?

This is another really interesting area.

Recent research has also shown that supplementary strength and plyometric training may improve running economy, durability and fatigued high-intensity performance.

Now, this doesn’t mean strength training replaces running.

Running specificity still matters enormously.

But strength training may help improve:

• force production

• tendon stiffness

• stretch-shortening cycle efficiency

• fatigue resistance

And importantly, it may help preserve these qualities later in prolonged exercise.

That’s a different conversation from simply “does strength training improve running economy?”

The question may actually become: Can strength training help you maintain performance under fatigue?

Durability Isn’t Just Physiology

This is where things become more complex.

Because late-race breakdown is not always purely a durability issue.

Fueling matters. Pacing matters. Hydration matters. Sleep matters. Non-running load matters.

All of these factors likely influence durability.

And clinically, this becomes really important.

Because when we see a runner fading late in a race, we need to ask:

• Is this poor durability?

• Poor fueling?

• Poor pacing?

• Insufficient training volume?

• Or simply an athlete exceeding current capacity?

The answer is often multifactorial.

Why I Think This Matters Clinically

I think durability has major implications not just for performance, but potentially injury risk too.

Because many running injuries don’t occur when athletes are fresh.

They occur once mechanics, stiffness, coordination, and force production begin to deteriorate under fatigue.

That may explain why some athletes tolerate shorter sessions well but repeatedly break down during longer runs or late in training blocks.

I also think it changes how we view marathon preparation.

Preparing for the marathon isn’t just about building fitness.

It’s about preparing your body to preserve that fitness under prolonged fatigue.

That’s a very different lens.

Final Thoughts

Durability is still an emerging area of research, and there’s a lot we still don’t know.

But I think it’s one of the most exciting concepts currently developing in endurance performance.

Endurance sport isn’t simply about how fast you can run fresh.

It’s about how much of that physiology you can hold onto once fatigue arrives.

And in the marathon especially, that may be the difference between holding pace… and completely falling apart late in the race.

To learn more about this, listen to The Rehab Runway podcast where Luke interviewed researcher Michele Zanini

References

• Zanini, M., Jones, A.M. and Nybo, L. (2025) ‘Viewpoint: Durability, fatigability, repeatability, and resilience in endurance sports: definitions, distinctions, and implications’, Journal of Applied Physiology, 139, pp. 1714–1715.

• Zanini, M., Folland, J.P. and Blagrove, R.C. (2025) ‘Regular long runs and higher training volumes are associated with better running economy durability in performance matched well-trained male runners’, Medicine & Science in Sports & Exercise.

• Zanini, M., Folland, J.P., Wu, H. and Blagrove, R.C. (2025) ‘Strength training improves running economy durability and fatigued high-intensity performance in well-trained male runners’, Medicine & Science in Sports & Exercise.