by Ed Ayres
So, as I glanced at the sun up behind me a bit west of the zenith, my neck was noticeably sore—thanks to the Appalachian Trail, no doubt. But that glance had also been triggered by the demand for another, equally critical, kind of balance—in my internal temperature. The running body burns calories relentlessly—first the glycogen already in the muscles or delivered from the liver; then the high-calorie replenishment you carry or pick up at aid stations, to the extent that you can assimilate it fast enough; and then body fat. If you go long enough even to deplete the fat, like one of Joseph Stalin’s gulag-bound prisoners forced to march across Siberia in winter (whose calories were also being burned to keep him from dying of hypothermia), then the body begins cannibalizing itself—consuming its own muscle for fuel. When it does that, it is doing what our industrial economy has been doing for the past century—spending down the planet’s finite resources. A runner will do well not to follow the example of the industrial economy.
The interconnectedness of all things (foot bone, knee bone; head turning, persistence hunting; envisioning, civilization building) never ceased to amaze me, sometimes with delightful and enlightening revelations, but other times with moments of sheer head-shaking chagrin. Body temperature, for example, “connects” not only to the obvious function of maintaining energy-use efficiency (not having to steal blood from the legs in order to keep the critical organs functioning on a freezing day, etc.), but also to not-so-obvious things such as your ability to tie your shoes. One frigid winter day in Virginia, I had the unnerving experience of having one of my shoelaces come untied in the middle of a race—the Swinging Bridge 50K, if I recall. This never happens to me; I always double-bow my laces. But in this race the course followed a little-used path through heavy undergrowth, and a vine or something must have gotten tangled with the lace and pulled it loose. I stopped to tie it, and—lo—my fingers, despite the gloves, were too frozen to grip the lace. Most of the blood had abandoned my fingers to do more important work inside, and the little finger muscles were helpless. I had to put my hands inside my shirt and under my armpits to warm them for a while, and it must have been ten minutes before I could finally get the shoe tied. Such a little thing! It was like another of those folk-wisdom proverbs about connection: For want of a shoe . . . the kingdom was lost.
So, cold can be a runner’s adversary. But then, so can heat. Excessive heat, too, shunts blood and consumes calories. If it’s a hot day, some of the blood may have to be diverted from the working muscles to carry heat to your face and neck (where the carotid artery brings heat very close to the surface) or to other unclothed surfaces, to get rid of it via evaporative or convective cooling. And then, too, the muscles—getting less blood and therefore less oxygen and fuel—have to work harder to keep up the same pace. Efficiency falls. And if it falls far enough, you fall too.
I was now around thirty-three miles into the race, with new challenges no doubt awaiting me like trolls, and I couldn’t help recalling—with wistful bemusement—all those times I’d heard it said, and in fact said myself, that one of the great appeals of running is its simplicity. In 1977, extolling the virtues of running in one of the first issues of Running Times, I wrote: “As the world gets more complicated, people become more appreciative of the things that remain simple—and few things do. Running is in some ways the simplest of all sports. All you have to do, to run, is open the door and go out.” And then there were all those little encouragements you’d hear from people encouraging their girlfriends or husbands or coworkers to give running a try: “Just put one foot in front of the other! It’s that simple!”
I now understood that while that wasn’t really wrong, it was far from the whole story. As an editor working for scientists, I learned very well how profoundly appealing—but also how much like a mirage—the notion of simplicity can be to anyone searching for answers. For scientists, simplicity is the holy grail of research. If a theory is too complicated, it is suspect. And if a phenomenon can be well explained by a very simple theory that has no contorted equations or loose ends, that theory is described as “elegant.” In the workaday world of real research, though, science is rarely simple and never final. Running is simple to behold, no doubt in part because it has been honed by a hundred millennia of evolution. In look and feel, it can indeed be elegant. Yet scientists like Carrier, Bramble, Lieberman, and Heinrich—and scores of others—had by now devoted thousands of days to studying the biomechanics, physiology, anthropology, and neurology of this simplest of human activities, and the complexities only continued to grow.
From my own limited perspective, informed by my work with the ecology of the human footprint writ large, I knew that while energy supply was not the whole story for either a sustainable society or an enduring individual, energy efficiency—though a far bigger factor than most people thought—wasn’t the whole story either. In my mouth, I still had a taste of the potato I’d picked up at Snyder’s Landing—it’s amazing how long it can take me to chew and swallow a bit of solid food when I’m running and breathing through my mouth—and that taste represented a disconcerting prospect for the miles ahead. I was a very tired sixty-year-old man, and even the most elementary math said that neither new energy supply nor the most highly efficient use of the little energy I had could possibly keep me going this way for another three hours. I had to find a way, and then it struck me: That last taste of potato in my mouth might offer a clue.
10
A Boiled-Potato Miracle
Burning Fat in a Carbohydrate Fire: A Secret of the Inca Messengers
The implications of the energy-efficiency secret for human physiology, as well as for the human economy at large, were huge. I knew that, in endurance training, refueling too readily would be counterproductive, though this is what some athletic energy-supplement companies—echoing their fossil-fuel brethren—were suggesting. If the runner’s body came to rely on constant new supply, it would not be compelled to adapt to greater efficiency in the use of a very limited supply. Again, the trick was balance: In training (as opposed to racing), you don’t want to let yourself run out of fuel totally, but you do need to make yourself adapt to running farther with less. Then, when you race, you have both optimal supply and optimal efficiency, which should produce a better performance than just one or the other.
At Snyder’s Landing, half an hour earlier, looking for my potato, I felt a bit like a vegan dinner guest eyeing the Thanksgiving turkey dinner at his meat-loving cousin’s home. The aid-station crews at the JFK 50 Mile have a friendly competition each year to see which crew can give the runners the greatest support and encouragement (the one at Taylor’s, the station coming up next at mile 38, called itself the “38 Special”), and the resulting spread laid out on the tables looked to me like excess, although maybe that was just me.
Recalling the stop at Snyder’s reminded me of an ultra I had run in Italy a few years ago, called the 100km del Passatore, where over ten thousand people had participated—about a third of them running, the others hiking. Ultras are much bigger in Europe, where maybe the culture isn’t quite as frantic and workaholic as in the US and more people take time for slow pleasures. The Del Passatore had started in the main square of Florence, later in the day than most American races do, then climbed up and over the Apennine Mountains through the evening and night. Along the way, we passed villages where people had set up encampments by the roadside to offer us a continuous repast of Northern Italian cuisine—sausage-and-prosciutto pie, beef carpaccio, pine-nut-stuffed dates, pork-stuffed pasta, and ample wine. Village after village, it never ended, and if some of the hikers behind us had wished, they could have arrived at the Roman ceramics-making city of Faenza, where a large reception awaited us for the finish, completely drunk. There was a place in life, I could see, for long hikes with good food and wine. But not if you wanted to run like a persistence hunter.
In my marathon-running days, I often passed up refueling altogether, depending on that adapt-to-limited-fuel training strategy to
get by with just the glycogen already stored in my muscles and liver when I went to the starting line. When I first tried ultras, I unthinkingly assumed the same strategy would work. It didn’t. At least some refueling is needed if you go beyond your glycogen limit, which for most marathoners seems to be somewhere around twenty to twenty-two miles. What I would eventually learn is that just as there is an enormous leap of capacity as you shift from sprint metabolism to aerobic metabolism, there’s another large leap that can be taken from marathon-range efficiency to the kind that can enable a well-trained man or woman to keep running for twenty-four hours, or even ten days, with only the briefest stops. At this level, humans can outlast horses or wolves. What happens is that, with proper training and fueling, the body shifts from burning carbohydrates as the primary fuel to relying more strongly on fat. Paradoxically, ultrarunners have (and need to have) less body fat than most other people—yet the little we have is of great value. Fat is the ultrarunner’s secret friend.
I had learned about this in two stages—one brutal, the other easy. In the first, a little before I turned fifty, I ran the Angeles Crest 100 Mile over a very rugged part of the San Gabriel Mountains and reached complete exhaustion at seventy miles, where there was a big aid station at the foot of Mt. Wilson. The next four miles would be an unrelenting climb to the top of the mountain. How do you run up Mt. Wilson after running seventy miles over other mountains? I collapsed onto an army cot, nauseated at the very sight of water or food, my stomach in rebellion, my glycogen and blood sugar both long exhausted, wondering how in the world to refuel short of an intravenous injection. After about half an hour of introspection, it suddenly came to me that there was one thing I could eat without hurling—a boiled potato! And while I couldn’t stand water, I could drink tea! Like a quarterback throwing a Hail Mary pass, I had gone deep with the Sheehan mantra—listen to your body—and an answer had come! I asked a volunteer if by any chance in the world they might have a boiled potato and some tea, and to my amazement they did. Evidently others had made this discovery before me. And thank heaven for aid station workers. I ate the potato, drank two cups of the tea, got to my feet, toddled out to the trail, and slowly worked my way from a lurch to a jog. And then, miraculously, I ran the final thirty miles on what could not have been more than ten potato-fueled calories per mile. I knew I’d have to be violating the laws of physics to do that on less than around 130 calories per mile. At the finish in the Rose Bowl, I was thrilled but mystified.
The second phase in my edification took only a minute, although it didn’t happen until a couple of years later, when I mentioned my mystification about the potato to a veteran Virginia ultrarunner, Tom Corris. Tom smiled and told me about a phrase he’d heard from runners who studied exercise physiology: “Fat burns in a carbohydrate fire.” Through a complex process, a small amount of carbohydrate can act as a kind of catalyst to facilitate the burning of fat, which is almost always in good supply in the body. In short, if you’re well trained, you don’t need to supply your body with another five thousand calories of fuel to go another five thousand calories’ worth of distance; you may only need three hundred calories, if it’s a form of carbohydrate your stomach can stand and if you’ve done enough long-distance training to adapt your metabolism so it will use that carbohydrate to ignite the energy-rich fat you already have. No matter how admirably lean you might be, unless you are actually starving, you still have enough fat to go for days. And what the carbohydrate does for that fat is like what kindling does for an oak log. At the Angeles Crest 100, I now understood, that little potato had set free my inner hunter. Back there at Snyder’s Landing, I had thought, I don’t want a feast. But I sure could use a boiled potato.
Some months after my conversation with Tom Corris, I found a Web site that provided a physiological explanation that did not just rely on a kindling-and-oak log analogy. It was from the American Council on Exercise:
Fat burns in the flame of glucose, meaning that fat can only enter the mitochondrial energy pathways when there is enough of the end-product of glucose catabolism—pyruvic acid—along with oxygen, also present in the muscle cells. One of the key physiological adaptations of improved aerobic fitness is an enhanced capacity to utilize stored fat for ATP production. Functionally, it means that the lactate threshold is not reached until a much higher absolute intensity (caloric expenditure) is reached. This allows for more intense, as well as long duration, aerobic exercise.1
Translation: When you’re running under normal conditions, some of the carbohydrate you consume breaks down to a substance (pyruvic acid) that then enters tiny power plants (mitochondria) within the muscle cells, where it meets up with the oxygen you inhale to convert the fat and other nutrients you’ve consumed into carbon dioxide and water—exhalation and sweat—thereby releasing energy. In this process, the nutrients are all broken down into a molecule called adenosine triphosphate (ATP), which is the immediate driver of muscular contraction. If you’re exhausted and all you’ve got left in those tiny power plants is fat, you still need some of that pyruvic acid to turn it into ATP. A little carbo intake can keep those millions of power plants firing.
A coda to my Angeles Crest story: One day not long ago I learned a little more about the Chasquis, those mountain-running messengers of the ancient Incas whose territory spanned the Peruvian Andes where wild potatoes grew. When the Chasquis were on the run, it seems, wild potatoes were their primary fuel. The potatoes provided the glucose that produced the pyruvic acid that combined with that Andean mountain air to produce the ATP that kept them on the move.
A few hundred yards ahead, I noticed a guy running without a shirt. The air was still cold, but running generates a lot of heat. And some men (I’m always conscious of how unfair this is to women, who aren’t granted the same freedom) take off their shirts whenever it gets even a little warm. While heat buildup may be what the guys think they’re responding to, I think there’s something else as well. In the evolution of awareness, one of the key developments was an epochal movement from the very hairy body of an ape to the bare skin of a modern human. To a human, naked means more than just “without clothes,” in the sense that a dog or bear is without clothes. Feeling the sun and air on our bare skin can have a powerful hold on us. Some of that traces to implied sexuality, in the same way that our ability to envision the future may trace to hunting the not-physically-visible prey that has disappeared around the bend ahead. But there’s another powerful trace as well.
In their gradual migration from the shade of forest canopy to the hot sunlight of open grassland, our hominid ancestors had to make tremendous physical adaptations. Yes, they may have had to get up on two limbs in order to see over the high grass, or in order to free the other two limbs to carry weapons or water or their babies. At the same time, though, they no doubt had to adapt to the consequences both of being out in open sunlight and of traversing much longer distances than they had ever traveled as apes. Fast walking—and eventually, running—generates a lot of heat. The body of a runner, like the engine of a car, has to get rid of waste heat as rapidly as it’s generated, or else fail.
I learned this the easy way, by running in a temperate, East Coast climate. One January in Philadelphia, for example, I ran a twenty-mile race during a blizzard. The air was below freezing, and I wore a hooded sweatshirt and shorts. A photographer for the Philadelphia Evening Bulletin, happening to see me go by, considered my bare legs enough of a curiosity in this driving snow to take a picture, which appeared on the front page of the next day’s paper—and then was reprinted on an inside page the following day, along with the caption “Who Is He?”—as if I were some extraterrestrial who didn’t understand cold. But, in fact, I understood it well enough to know that if I wore a hood over my head (which is a major heat-radiator) in order to keep my ears from freezing, I needed some other part of my body to serve as an efficient radiator. Running at a rate of about six minutes per mile, I was generating enough heat that the cold air on my legs nicely b
alanced the high heat output.
If I tried to run at that pace on a hot African savanna, the challenge would be much harder. I would have to cope not only with the heat generated by my metabolism, but also that of the sun’s direct radiation on me. But that’s where the real adaptive genius of naked skin comes into play. The human body, as presently configured, has not just one cooling mechanism, but three. A car has a radiator. But a man or woman in motion, in addition to radiating heat directly, can also cool by convection, which is the transfer of heat by the movement of skin against air or of air against skin (the “breeze” effect), and by evaporation of sweat. The convection and evaporation work much more effectively with bare skin than with heavy hair or fur. One of the reasons we humans are among the most enduring of all large animals is that we are so naked. Give us sufficient water to keep sweating, and we can run for a very long time without overheating. Our nakedness was one of the keys to our ability to outrun woolly mammoths, given enough time to let the heat in the bigger animal build up.
When a three-year-old mischievously flings off all his clothes and runs across the lawn or beach, he’s not just being mischievous; he’s getting at least a fleeting sense of something quite primal in his human nature. The child is probably hardwired to feel pleasure in the movement of air on skin. I know it’s true for me. And if this pleasure is innate, I suspect the reason is that this direct contact of skin with air is part of a larger set of contacts between body and environment that were selected for their capacity to provide critical information, as well as to provide cooling or other homeostatic services. The selection was reinforced by pleasure, and eventually by the conscious prospect of pleasure. Other parts of this information-gathering system include the feel of bare feet on earth (vestiges of which are often enjoyed by gardeners or beachgoers, as well as by some runners), and all the other sensory or kinesthetic connections that still affect what we like or don’t like.
