Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance

by Alex Hutchinson

The limits of endurance running, according to physiologists, could be quantified with three parameters: aerobic capacity, also known as VO2max, which is analogous to the size of a car’s engine; running economy, which is an efficiency measure like gas mileage; and lactate threshold, which dictates how much of your engine’s power you can sustain for long periods of time.

Avoiding thirst, rather than avoiding dehydration, seems to be the most important key to performance.

In his work with elite marathoners, Stellingwerff aims for 3 to 6 percent dehydration, depending on weather and individual tolerance.

To me, the primary message is that, like oxygen and heat and (as we’ll discover) fuel, the loss of fluids first makes itself felt via the brain. Thirst, not dehydration, increases your sense of perceived effort and in turn causes you to slow down. Eventually, the physiological consequences of dehydration assert themselves, increasing the strain on your cardiovascular system and pushing your core temperature up as the volume of blood in your arteries decreases. But that only happens if you’ve already ignored the signs of thirst.

Cheung hopes people will take from his study, and from the spate of recent research challenging hydration orthodoxy: not that you shouldn’t drink when you have the chance, but that you shouldn’t obsess about it when you don’t. “It’s one less psychological crutch,” he says, “to hold you back from a top performance.”

According to filmmaker and former elite runner Michael Del Monte, who spent months in the heart of Kenyan running culture while filming the documentary Transcend about the rise of marathoner-turned-politician Wesley Korir, it comes down to belief. Even the humblest Kenyan runner, he noticed, wakes up every morning with the firm conviction that today, finally, will be his or her day. They run with the leaders because they think they can beat them, and if harsh reality proves that they can’t, they regroup and try again the next day. And that belief, fostered by the longstanding international dominance of generations of Kenyan runners, becomes a self-fulfilling prophecy.

That lesson, he recalled, stuck with him—first as an athlete and later as a scientist: “You have to teach athletes, somewhere in their careers, that they can do more than they think they can.”

As he disappeared from our sight lines on the press truck, we shook our heads knowingly: confidence is great, but the marathon punishes overconfidence with Old Testament severity.

If you want to run faster, it’s hard to improve on the training haiku penned by Mayo Clinic physiologist Michael Joyner, the man whose 1991 journal paper foretold the two-hour-marathon chase: Run a lot of miles Some faster than your race pace Rest once in a while

If I could go back in time to alter the course of my own running career, after a decade of writing about the latest research in endurance training, the single biggest piece of advice I would give to my doubt-filled younger self would be to pursue motivational self-talk training—with diligence and no snickering.