There are a lot of measures we use in endurance sports to compare one another or gauge our expectations. But one of them is slowly becoming the best predictor of performance. Here's what you should know about fatigue resistance and why it matters.
Everywhere in endurance sports right now, people are talking about fatigue resistance — and for good reason. It's a rare, relatively new idea: the one that explains why two equally fit athletes can have completely different races at the last mile.
Nobody has done more to define, measure, and prove it than David and Megan Roche. David rewrote the Leadville record book with it.
What is fatigue resistance?
Fatigue resistance is your ability to hold your effort — pace, power, output — late in a race instead of it feeling compromised or reduced.
You can think of fatigue resistance as the gap between what you can do fresh and what you can do three hours in.
The Roches built a simple field test around it over a decade ago: run moderate for 90 to 120 minutes, then go hard for 10 minutes, and compare that effort to what you can do fresh.
The offset between the two is your fatigue resistance number, and they've found it can predict long-race performance better than almost anything you can measure while rested.
That last part is the whole point. Two athletes can have the same fitness, the same pacing, the same race plan — and completely different results at mile 20. Fitness tells you what you can do fresh. Fatigue resistance tells you what you'll have left when it matters.
(David wrote about how he tested and transformed this aspect of his training in his blog, which set the course record at Leadville.)
Good news: Fatigue resistance is trainable, and the fastest lever for improving it isn't just more training. It's more carbs. That's the exact move David made.
More carbs = more fatigue resistance
Your body can only store so much glycogen — the fuel your muscles burn during hard efforts. Once it runs low, your pace drops even if your legs still feel capable, because your muscles simply don't have the fuel to keep firing at the same output.
The fix is training your gut to handle more carbs per hour of exercise, then taking in that much on race day. Do that in training, and you get more out of your training. Athletes who increase their carb intake are usually the ones who can hold pace for longer periods.
Your Carb Gel:
Precision Fuel & Hydration PF 30 Gel — Easy to titrate your carbs, as each gel gives you 30g of carbs and is one of our most loved gels athletes consume.
SiS Beta Fuel Gel — One of the OGs of high-carb. Gives you high carbs (40g) in a smooth format.
Amacx Turbo Gel (with caffeine) — Liquidy high-carb with a hit of caffeine.
Maurten Gels — Uses hydrogel technology to help you absorb a high level of carbs without GI distress.
The Big Takeaways:
Train your gut: Practice your target carb intake in training long before race day. Your gut adapts to handling more carbs the same way your legs adapt to more mileage.
Fuel on the clock: Take a gel every 30–45 minutes starting early in the race, before you feel like you need it.
Gradually up your intake: If you've been taking in 30g of carbs an hour, don't suddenly jump to 90g on race day. Build up your tolerance slowly over a few weeks of training.
Test yourself: Want your own fatigue resistance number? Run the Roche test — 90 minutes moderate, then 10 minutes hard — once now and once after a month of better fueling. Watch what happens to the gap.
