Book Review: Endure
“Do you notice he’s not dead?” he asked. “It means he could have run faster.”
Endure is by Alex Hutchinson. The subtitle is “Mind, Body, and the Curiously Elastic Limits of Human Performance”.
Mind and Body
The thesis of Endure is that while working out, the mind plays a critical role in deciding when we feel tired and ready to give up — “fatigue ultimately resides in the brain”. Or in other words, “anything that moves the “effort dial” in your head up or down affects how far or fast you can run.” Another basic, brutal expression of this theory is in the epigraph at the head of this review.
There’s lot of discussion of the various science that suggests that this is the case. Consider this experiment of cyclists:
In experiments…cyclists started at a slower pace right from the outset when the temperature was high—and crucially, the amount of muscle recruited by the brain was also lower within the first few minutes. At a conscious level, the cyclists were trying just as hard (as their reported level of effort indicated), but fewer muscle fibers in their legs were contracting thanks to their central governor’s inbuilt caution.
Or another cycling experiment:
Before one of the tests, the subjects spent 90 minutes performing a mentally fatiguing computer task…
After the mentally draining computer game, the subjects gave up 15.1 percent sooner in the cycling test, stopping on average at 10 minutes and 40 seconds compared to 12 minutes and 34 seconds. It wasn’t because of any detectable physiological fatigue: heart rate, blood pressure, oxygen consumption, lactate levels, and a host of other metabolic measurements were identical during the two trials. Motivation levels, as measured by psychological questionnaires immediately before the cycling tests, were the same—helped along by a £50 prize for top performance. The only difference was that, right from the very first pedal stroke, the mentally fatigued subjects reported higher levels of perceived exertion. When their brains were tired, pedaling a bike simply felt harder.
Or, this experiment that involved, uh, more cycling:
At an average target power of 242 watts, which corresponded to 80 percent of their peak power, the players lasted for about 10 minutes, with cash prizes to ensure they fully exhausted themselves. As soon as they gave up—within three to four seconds—they were asked to see how much power they could generate in a single 5-second burst of pedaling. Curiously, although they had just declared themselves incapable of producing 242 watts, they managed to average 731 watts during this five-second sprint.
In essence, a part of athletic training is essentially training yourself to ignore pain:
[Researchers] have shown that regular physical training, especially if it involves unpleasant high-intensity workouts, increases your pain tolerance.
Training can make you better at resisting pain. So then can practicing resisting pain make you better at training?
Morris and O’Leary’s study…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?
Hutchinson goes on to attempt some of these training methods, like using the “mentally draining computer game” (mentioned above) prior to going on long runs. Although pain is an important signal from your body, you can learn to ignore it in a healthy way. For example, every time I run a fast mile, I really feel like I don’t have the endurance to go faster. But then remember the quote from the top of this review, again: “Do you notice he’s not dead?…It means he could have run faster.” I feel like I’m going really hard, and then, when I finish, all I need is ten seconds with my hands on my knees before I can walk over and grab my stuff and jog home. So clearly, these particular feelings of fatigue are ones that I can safely ignore, and push myself a little harder.
He describes the experience of that “mentally draining computer game” during a Brain Endurance Training session: “I have that cotton-headed feeling of total mental exhaustion that’s usually the cue to flop down in front of the TV for a few hours.” To me, this was actually an intriguing phrase: I associate that feeling with times in my life when I’m really pushing myself and learning so many new things that I’m getting truly worn out during the day. Like my first few months living in Shanghai, when I was doing lots of new things at work and studying Chinese for an hour each way on the subway. Some nights I’d come home and just lay on my bed and stare at the ceiling for a while before I transitioned into my evening.
I don’t remember if Hutchinson ever mentions this himself (if so, I didn’t highlight it), but there’s both a mental and a physical aspect, so to speak, to the thesis of mental fatigue. The mental aspect is what I’ve quoted above: the fact that you could go harder if you overcome your brain telling you to stop.
But there’s a physical/muscular aspect too: if you overcome your brain telling you to stop, and run faster, then you’re successfully training harder. And when you train at those higher intensity levels, your body will adapt to that level of activity, and you’ll grow stronger and faster. In other words, you may need to overcome mental fatigue to run a 5:30 mile, but once you’re running those miles in training, your body will adapt — you grow physically stronger and then need less pain-ignoring mental strength to run the same speed. The two pathways complement each other in leading to performance improvements.
The Body’s Real Limits
There are limits to the mental fatigue theory. Studies show that you use the vast majority of your muscular strength — it’s not like you’re only using ~10% of your strength in normal activities, and waiting until your baby is trapped under a car before you actually put all of your muscles to use:
While his subjects voluntarily contracted their thumb muscles, he superimposed a brief electrical twitch. If the voluntary contraction was relatively weak, the force would jump significantly when the twitch was added; but for stronger voluntary contractions, the size of the twitch got progressively smaller. And for maximal contractions, the brief electric shock didn’t add any force at all, suggesting once again that no extra muscle remained unused...
Overall…most healthy people can achieve “voluntary activation scores” of close to 100 percent…typical scores for all-out quadriceps contractions are 92 to 97 percent, and anything less than 90 percent suggests something has gone wrong with the test. Under normal conditions, in other words, we’re utilizing pretty much all the strength our muscles have to offer.
Part II of Endure is titled “Limits” and was full of truly wild anecdotes and scientific studies. The six chapters in Part II are titled, simply, “Pain”, “Muscle”, “Oxygen”, “Heat”, “Thirst” and “Fuel” and are full of stories of: people who survived a week in a desert with no water, people who set free diving or breath-holding world records (“The record for breath-holding after inhaling pure oxygen, a feat made famous by magician David Blaine’s 17-minute hold in 2008, now stands at 24:03, by Spanish freediver Aleix Segura.”), people who climb Mt. Everest with no supplemental oxygen, and more (including, of course, the guy who lifted a car).
In summary, it’s true that the limits are there, but it’s also true that your brain shuts you down before you really get close to those hard-and-fast limits.
Hydration and Nutrition
I’d read in Good to Go that in modern-day distance running, over-drinking is more prevalent than dehydration. Endure explains the science in more detail — it’s pretty interesting.
There was a pseudo-scientific idea in the past decades that in order to stay hydrated, you should try to lose no more than 2% of your body weight during a run. But now that seems to be an unrealistic suggestion. Top marathoners can sweat out about 3 liters per hour:
Like Salazar, Gebrselassie sweats at a prodigious rate: in one lab test, he hit a rate of 3.6 liters per hour, which is among the highest ever recorded.
But, their body can only process about 1 liter of water per hour:
During their pre-Olympic testing in 1984, he and his colleagues had estimated that Salazar’s “gastric emptying rate,” which determines how much fluid can pass through the stomach for absorption from the small intestine, was about one liter per hour while running. Given that his sweat rate was three times higher than that, there was never any chance he would be able to limit his fluid loss to 2 percent.
So you’re bound to lose water and weight while we’re working out in heat. But, the situation isn’t so bad — the body has its own ways to regulate how much water is in your system:
for every pound of weight lost, the amount of water circulating in the body [drops] by only 0.2 pounds…
The chemical reactions involved in burning fat and carbohydrate produce two key by-products: carbon dioxide, which you breathe out, and water—which actually adds to the amount of fluid available in your body. Even more significant, your body stores carbohydrate in your muscles in a form that locks away about three grams of water for every gram of carbohydrate. This water isn’t available to contribute to essential cellular processes until you start unlocking the carbohydrate stores, so your body sees it as “new” water when it’s released during exercise…in 2007 scientists estimated that a marathoner could conceivably lose 1 to 3 percent of his or her body mass without any net loss of water.
However, dehydration is still a real thing. And feeling thirsty is still undesirable, especially since it adds to that mental fatigue load on your brain. Endure and Good to Go have the same suggestion: drink when you feel thirsty, and don’t drink if you don’t feel thirsty.
On the nutrition side, Hutchinson says that for top marathoners, “relatively unsexy talents like the ability to scarf down prodigious amounts of calorie-rich food and keep running without throwing up are absolutely crucial.” When you’re using that much energy, you need to refuel, too:
60 grams an hour (about 250 calories) is pretty much the maximum amount you can absorb during exercise.
But…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.
There’s a chapter about how the body burns carbs for energy during intense workouts and fat during less intense activity. However, the body can be trained using high-fat, low-carb diets to tend towards burning more fats at any level of activity (although it is a less effective fuel source for high-intensity activity). This can be beneficial because you can go much further without re-fueling:
…a well-prepared athlete might be able to store 2,500 calories of carbohydrate…whether you like it or not, you’re lugging at least 30,000 calories of fat with you.
Those Studies Though
Endure is a book full of crazy stories and frankly crazy, even unethical, scientific studies. Here’s a partial recap.
Did you know that animals instinctively respond to being underwater by lowering their heart rate (among other bodily changes). Here’s how one scientist chose to investigate that phenomenon:
Something close to magic occurs when you submerge your face in water—a vestigial reflex that we share with all mammals, both terrestrial and aquatic. In 1894, Nobel Prize–winning physiologist Charles Richet began publishing the results of a series of gruesome experiments in which he tied off the windpipes of ducks and timed how long they took to die. Some were strangled in open air, and lived for an average of 7 minutes; others were dunked underwater and survived for an average of 23 minutes.
I suppose we shouldn’t be too surprised that there was some seriously unethical science going on in early 1900s South Africa. This is how one doctor studied humans’ ability to adapt to heat (to support a mining company’s efforts to get more out of their manual laborers):
Dreosti converted an unused hospital ward into a heat chamber crisscrossed with perforated pipes releasing steam, where up to fifty workers at time could undergo the “Heat Tolerance Test” he devised. The test involved stripping naked and shoveling piles of rock back and forth with a partner for one hour at a temperature of 95 degrees, overseen by a “specially trained native ‘Boss Boy.’” After testing 20,000 workers in his chamber, Dreosti was able to divide his subjects into three groups based on how high and how quickly their body temperature rose, and assigned these groups either 4, 7, or 14-day acclimatization periods.
The way you respond to heat might depend not just on your body temperatures but also on your brain temperature (in other words, keeping your head cool is as important as keeping your muscles cool). How did we find that out, you ask? This one is relatively tame:
Earlier studies with goats and dogs whose brains were cooled by irrigating cold water through their noses had suggested that brain temperature, rather than core temperature… is what determines your ultimate thermal limits.
As mentioned above, there’s a chapter that discusses how the body uses fat and carbohydrates for fuel. Here’s one anecdote mentioned there:
A 1973 journal article by a Scottish doctor reports the case of A.B., a twenty-seven-year-old man who weighed 456 pounds before undertaking a medically supervised fast lasting 382 days, during which he lost a remarkable 276 pounds.
The way we interpret feelings of thirst is also not completely based on an objective state of your body, but depends on mental/psychological processes. Feeling like you’re drinking water can improve your feelings of fatigue more than actually drinking water does:
A famous 1997 study at Yale had subjects exercise for two hours to induce dehydration, then allowed them to drink and monitored the changes in perceived thirst and antidiuretic hormone, the two key regulators of plasma osmolality. Then they repeated the trial, but inserted a tube down through the nose into the stomach to vacuum out the water as soon as it was swallowed. The result: thirst and antidiuretic hormone secretion both decreased anyway, presumably in response to the sensation of water flowing down the throat. And when they reversed the experiment, sending the same amount of water down the nasogastric tube instead of letting the subjects swallow it, it was less effective in quenching thirst even though the water was allowed to stay in their stomachs.
This, in turn, helps to explain why a later study found that swallowing small mouthfuls of water—too small to make any difference to overall hydration levels—boosted exercise performance by 17 percent compared to rinsing the same amount of water in the mouth and then spitting it out.
Training Tips
One reason I read this book was to learn how to train better. Overall, Endure is more about ultimate human limits, and isn’t a book with hard-and-fast training recommendations. Also, it doesn’t discuss how to train for explosiveness; this book is about endurance over a longer period. Although that needs a caveat — explosiveness and endurance overlap:
Even in repeated all-out weightlifting efforts...studies have found that we can’t avoid pacing ourselves: your “maximum” force depends on how many reps you think you have left.
But there are still a few ideas that I took away:
Motivational self talk. Hutchinson says “If I could go back in time to alter the course of my own running career…the single biggest piece of advice…would be to pursue motivational self-talk training—with diligence and no snickering.”
Brain Endurance Training. Although it’s not yet backed up by clear evidence, the idea of training your brain to withstand the feelings of tiredness is enticing to Hutchinson, and is to me, too. I’ve downloaded an app with a “mentally draining computer game” to train with before a few runs each week.
Caffeine. I don’t use caffeine. Maybe I should? Just a little? “To prove the cyclists wrong, Burke and her colleagues designed a double-blinded, placebo-controlled test of low-dose caffeine during exercise—and discovered that it worked…”
Eat ice in hot weather to stay cool: “the “phase change energy” of ice melting to water in your stomach provides an extra cooling boost beyond what you would get from simply drinking a cold drink.”