Pain
Studies have mostly confirmed these findings: athletes, and especially endurance athletes, are consistently willing to tolerate more pain. Like Wolfgang Freund’s study of TransEurope runners, the results pose a chicken-and-egg question: do great athletes learn to endure more pain, or is their greatness a consequence of naturally high pain tolerance? While the truth undoubtedly lies somewhere between those two options, a curious footnote in Gijsbers’s results points toward the former. He retested the elite swimmers at three different times of year and found that they scored highest on the pain tolerance test in June, during their peak racing season; lowest in October, after their off-season; and somewhere in the middle during their regular training period in March.
Pain in training leads to greater tourniquet tolerance, and greater tourniquet tolerance predicts better race performance. Many athletes, of course, make this link intuitively. Triathlete Jesse Thomas, for example, learned to use his deep-tissue massage sessions as a form of pain training: “When I’m hurting like crazy,” he explains, “instead of blocking out the pain, I try to accept it, feel it as much as possible.”
Morris and O’Leary’s study will need to be replicated by other groups under different conditions before its results can be fully confirmed. But it suggests that, at least in recreational athletes, pain tolerance is both a trainable trait and a limiting factor in endurance. And it leaves a ripe and juicy question dangling for future researchers: can you get faster by simply training yourself to better tolerate or block out pain?
Muscle
Runners have a phrase for that feeling, though it doesn’t show up in dictionaries: to rig, as in “I thought I was going to win the race, but I started rigging on the final turn.” It’s derived from rigor mortis, the stiffening of the body after death, and it’s one of those words that perfectly capture an otherwise baffling sensation. Sometimes, when you’re watching a middle-distance race, you can see the exact moment when someone starts tying up (another euphemism in common use), as their stride shortens and their movements get jerky—and, if you’ve been in that situation yourself, you can’t help wincing in sympathy.
So why is it that your muscles fail you when you rig? The traditional explanation has long been that they are overwhelmed by a flood of lactic acid, which is produced when you’re working so hard that oxygen-fueled aerobic energy supplies can’t keep up with demand. After all, rigging typically occurs in events lasting between about one and ten minutes, which corresponds to the duration in which the highest levels of lactate are produced in your blood.
In a 2014 study, Markus Amann and Alan Light, along with colleagues at the University of Utah, tried injecting three different metabolites associated with intense exercise—lactate, protons, and adenosine triphosphate, or ATP—into the thumb muscles of ten lucky volunteers.
The concentrations they used varied from the “normal” concentrations that are always circulating in the body to the higher levels associated with moderate, vigorous, and extreme exercise. On their own, none of the three metabolites had any discernible effect. The same was true when they were injected in pairs, despite the fact that lactate plus protons is what makes lactic acid.
But when they injected all three metabolites together, the volunteers suddenly had the bizarre sensation of extreme fatigue and discomfort—concentrated in their thumbs. At low doses, the sensations reported by the volunteers were mostly things like “tired” and “pressure”; as the doses increased, the sensations ramped up in intensity and shifted to pain-related words like “ache” and “hot.” The results suggest that lactic burn isn’t literally the feeling of acid dissolving your muscles; instead, it’s a cautionary signal created in the brain by nerve endings that are triggered only in the presence of three key metabolites.
Oxygen
While the world’s best breath-holders certainly have some unique physiological skills and adaptations, it’s clear that initial progress in breath-holding—going from one minute to three minutes, say—is mostly a matter of simply accepting and ignoring the rising sense of anguish and panic. It’s in your head. At the same time, mountain climbers who don’t adapt well to extreme elevation—and this seems to be largely genetic, unrelated to fitness or experience—often get sick and sometimes die at the elevations
That’s not in their heads. In practice, assigning the blame to mind or muscles is an often hopeless and sometimes misleading task. After all, the brain is part of the body. This was a point emphasized by Michio Ikai and Arthur Steinhaus in 1961, when they studied the psychological effects of surprise gunshots on muscle strength “[P]sychology,” they wrote, “is a special case of brain physiology.” In other words, feelings and emotions and urges are as physiologically real as changes in core temperature or decreases in hydration, and are mediated by chemical signals. So when oxygen levels in the brain drop, are we compelled by failing neurons or safety circuitry to slow down, or do we simply decide to slow down? Is there a difference? Whatever the answers the outcome is clear. We slow down.
Heat
critical temperature isn’t quite as immovable as the initial studies suggested. Stephen Cheung, an avid cyclocross racer and environmental physiologist at Brock University in Canada, first explored this topic during his doctoral studies
In a military-funded experiment, he showed that fit, well-trained athletes could push to a higher core temperature during a treadmill test than less fit subjects—evidence that the brain’s temperature settings can indeed be altered.
Cheung’s most recent work provides even more remarkable evidence of the brain’s power. He and his colleagues put a group of eighteen trained cyclists through a battery of physical and cognitive tests at 95 degrees Fahrenheit. Then half the cyclists received two weeks of training in “motivational self-talk” specifically tailored to exercising in heat, which basically involved suppressing negative thoughts like “It’s so hot in here” or “I’m boiling,” and replacing them with motivational statements like “Keep pushing, you’re doing well.” The self-talk group improved their performance on one of the endurance tests from 8 minutes to 11 minutes—and in doing so, pushed their core temperatures at exhaustion more than half a degree higher. “We’re now pretty sure it’s not just a physical thing,” Cheung says of the critical temperature concept. “There seems to be a strong mental-psychological component to it.” The right frame of mind, in other words, allows you to push beyond your usual temperature limits: “Even if you’re already fit, you can still improve your perception of heat and how you perform in it.”
Thirst
You’ve heard the warnings. Drink now, because losing just 2 percent of your weight will hurt your performance—and by the time you feel thirsty, it’s already too late. This concept of “voluntary dehydration,” in which thirst is an inadequate barometer of your fluid needs, dates back to a series of wartime studies led by University of Rochester researcher Edward F. Adolph, which he summarized in a classic 1948 book called Physiology of Man in the Desert
With the outbreak of desert warfare in North Africa in 1941, Adolph and his colleagues were dispatched to the Sonoran Desert in California to investigate soldiers’ water needs. At the time, there was a widespread belief that you could train yourself to drink less water, which in turn would minimize “wasteful” sweat losses. Adolph and his colleagues debunked this notion and demonstrated that staying hydrated was important even for well-acclimatized desert veterans. But they also made a curious observation: in long desert marches of up to eight hours, even when the men were allowed to drink as much as they pleased, they finished the marches in a state of dehydration, having lost 2 or 3 or sometimes even 4 percent of their starting weight. Tank crews lost an average of 3 percent of their body weight after a few hours of simulated battle; the eight crewmen of a B-17 Flying Fortress returned from a two-hour low-altitude mission having lost 1.6 percent. The logical conclusion, then, was that you need to drink more than you really want to in order to avoid getting dehydrated.
Dehydration is a greater concern in longer races, because you have more time to sweat; heatstroke, in contrast, is most common in shorter races. That’s because your body temperature is primarily determined by your “metabolic rate”—that is, how hot your engine is running. In a thirty-minute race, you can sustain a fast enough pace to drive your core temperature way up, even though you don’t have time to get seriously dehydrated. In a three-hour race, in most circumstances, you simply can’t sustain a hard enough effort to push your temperature into heatstroke territory, even though you might get seriously dehydrated. It’s true that dehydration can push your temperature up a little bit. But the biggest factor dictating core temperature (aside from the weather conditions) is metabolic rate.
Fuel
The role that fuel stores play in the limits of endurance depends, of course, on what we mean by endurance. If you’re simply concerned with covering the greatest distance possible, without a particular focus on time or outsprinting rivals, then you might not care about pyruvate dehydrogenase. And in particular, if you’re in a situation when your ability to eat is severely constrained—an expedition across the Antarctic, for example, or a multi-day ultra-race where you can eat only what you carry—then the ability to tap into fat stores seems like a considerable advantage. The bigger the gas tank, the farther you can go and the less you need to refuel.
But if your view of endurance involves racing—squeezing as much distance as possible out of the unforgiving minute—then it turns out that your primary fuel-related concern is not how much but rather how fast. How quickly do your muscles burn fuel? How quickly can they access the various sources of fuel scattered throughout your body? And how quickly can you refill those reservoirs as you go?
The hydration plan that Haile Gebrselassie used when he set a world record of 2:04:26 at the Berlin Marathon in 2007, which involved drinking about two liters of fluid during the race. In practice, his plan was as much focused on fueling as on hydration. Of the two liters of fluid he planned to consume during the race, 1.25 L was sports drink (the rest was water), and he also took five sports gels, providing a total of between 60 and 80 grams of carbohydrate per hour. That number is significant, because scientists have traditionally figured that 60 grams an hour (about 250 calories) is pretty much the maximum amount you can absorb during exercise. The rate-limiting step is the absorption of carbohydrate from the intestine into the bloodstream.
But Gebrselassie was taking advantage of newly published (at the time) data showing that if you combine two different types of carbohydrate—glucose and fructose, for example—they pass through the intestinal wall using two different cellular routes that can operate simultaneously, enabling you to absorb as much as 90 grams of carbohydrate per hour.
Stomaching that much carbohydrate in the middle of a race is no easy task—that’s why Nike’s two-hour-marathon scientists spent so much time trying to help their athletes, particularly Zersenay Tadese and Lelisa Desisa, increase the amount they could stomach during training runs. The Nike team also mixed various drinks together to find personalized carbohydrate combinations that would maximize palatability and absorption rate for each runner. For the rest of us, glucose-fructose mixes are now incorporated in standard sports drinks from companies like PowerBar and Gatorade. If you can stomach more than 60 grams per hour, the higher absorption rate should help stave off the depletion of your glycogen stores and allow you to maintain a faster pace for longer without hitting the wall.
In theory, the math behind this sort of fueling plan is simple: the number of calories you need to ingest is the difference between how many you already have stored in your body and how many you want to burn. In practice, though, the body’s workings turn out to be considerably more complicated.
