100-Mile Races Test Limits Of Human Physiology

Theoretically, any reasonably fit person could run 100 miles, but he or she must train for it. After only three months of strenuous training, with runs three to five days a week that include one long session of 30 to 60 miles, the human body learns to use fuel and oxygen very efficiently. A well-trained endurance runner will have a resting heart rate around 43 percent lower than that of a sedentary person and body fat percentages 27 percent lower. Cardiac output, the amount of blood pushed through the circulatory system, expands by 75 percent, so that more oxygen is delivered. The amount of oxygen absorbed by organs and tissues also increases 30 to 50 percent, thanks to a doubling in the number and volume of mitochondria, energy generators in muscle cells. Trason says she not only tries to train her cardiovascular system but teaches her stomach to digest food on the run and toughens her legs to withstand hours on the trail.

Indeed, muscle cells work better with training; the number of capillaries multiplies, delivering more oxygen to the muscle tissue, while the amount of metabolic enzymes, proteins that break down carbohydrates and fats, increases 133 percent. Still, even the fittest have a hard time running 100 miles. "Unlike a marathon, where you can get away with less than optimal nutrition, the margin of error in a 100-miler is zero," says Lindsay Weight, a physiologist at the Sport Science Institute of South Africa in Cape Town, a leading center for research on endurance physiology. On average, an athlete who finishes Western States in 24 hours burns 16,000 calories and sweats 4 gallons of fluid.

It's difficult to take in that much food and water, but runners must try. Of these two essentials, the most critical is water. "You basically have to drink from start to finish if you want to avoid dehydration," Weight says. And it's not just a matter of replacing water: In sweating, the body may lose up to 3 grams of sodium an hour, resulting in imbalances of the key electrolytes, sodium and potassium, that regulate cell function. These imbalances, if extreme, can cause muscle cramping, nausea, fatigue, and confusion. Trason avoids dehydration by eating salty foods (pretzels are a great source of sodium) and carrying water bottles in her hands so she'll remember to drink every 15 minutes. In Western States and other races, runners are weighed en route and stopped by officials if they've lost more than 3 percent of their body weight, which is a sign that they are dehydrated.

Out of gas. Staying fueled during an endurance event is just as difficult. The body uses three sources of fuel--carbohydrates, protein, and fat. At first, protein, which is stored in muscle, supplies 10 percent of energy and body fat supplies 15 percent. The remaining 75 percent comes from carbohydrates stored as glycogen, a complex sugar formed by stringing glucose molecules together in the muscles and the liver. After six hours of continuous effort, the body has consumed most of its glycogen stores, and body fat becomes the primary energy source. But because fats are metabolized less efficiently than carbohydrates, someone who doesn't eat while running will literally run out of fuel.

"Carbo loading," a common runner's practice of eating a 70 percent carbohydrate diet for three to seven days before a race, helps stave off carbohydrate depletion by doubling the glycogen available to both muscles and liver. Eating during the competition helps refuel--but it may cause diarrhea and nausea, which occur when blood flow that would normally aid digestion is diverted to other organs. Trason considers nausea an inevitable part of racing. "The harder I work, the harder it is for me to eat. I just try to get down whatever I can." That includes syrupy athletic supplements like GU and PowerGel, hard candies, and even Coca-Cola, which, thanks to the caffeine, promotes fat metabolism. In races, aid stations along the way provide salty, high-energy snacks such as soup and baked potatoes.

Mastering the metabolic demands of endurance running is just one of the sport's many obstacles. A distance runner also breaks down muscle and tears up cartilage and ligaments. With each step, leg muscles and tendons absorb impacts two to four times a person's body weight and use that energy to generate the force that propels the body forward. With time, the mechanical stress disrupts muscle fibers, tearing them in many places. In addition, a runner's body starts breaking down muscle protein as blood glucose levels fall, using protein's building blocks, amino acids, for fuel. This cannibalization causes further damage. The trauma can be severe; biopsies of runners' leg muscle tissue after marathons clearly show necrosis, or cell death, and swelling. Muscle damage is rarely permanent, but it can take up to three months to repair. Runners describe the fatigue and soreness associated with this long-term tissue damage as "dead legs."

Long-term exertion also may damage muscles' mitochondria, a process that is frighteningly similar to the damage that occurs with aging. In studying an injured 27-year-old endurance athlete, physiologists Alan St. Clair Gibson and Mark Lambert, both from Sport Science Institute of South Africa, found that the athlete's mitochondria were so ravaged that they resembled those of a 60- or 70-year-old. Oxygen free radicals, highly reactive electrons that are a byproduct of oxygen metabolism, are a likely culprit, since they attack cell parts. According to Gibson, prolonged exercise may artificially age muscle mitochondria to the point that they stop working properly.

Sickening. Just as insidious is the toll endurance running exacts on the immune system. In a 1987 study of 2,311 Los Angeles runners, 42 percent of those training for a marathon reported at least one upper respiratory infection in the two weeks before the race. After the event, 13 percent got sick within two weeks, while only 2 percent of the control group, which trained but did not compete, developed infections. Just how exercise suppresses the immune system remains a mystery, but there are clues suggesting that cortisol, a stress hormone, may be involved, since cortisol levels are 15 times higher than normal in post-race endurance athletes. Cortisol is known to suppress the activity of killer T cells and neutrophils, which combat infection. Damage to white blood cells by free radicals and severe nutrient depletion may also be involved. Perhaps the immune system can't marshal itself to protect the body from infectious agents given its starved condition.

Weekend joggers, and even marathon hopefuls, need not worry that they are inflicting serious damage on themselves. According to Weight, damage doesn't accumulate until a person has run more than six hours. "That's why top athletes don't last forever," Weight says; an ultrarunner can expect to remain competitive for eight to 10 years. Trason plans to have surgery to remove scar tissue in her ankle, the product of years of high mileage, after this season and is taking time off to consider life beyond running, including whether she and her husband will have children.

Why is Trason so good, beating most of the men, including her husband (she was fourth overall in this year's competition)? She does have a physiological advantage: She is very light, weighing only 105 pounds at 5 feet, 4 inches. It takes less energy to move a lighter body and puts less stress on bones and tendons. But her greatest advantage may be determination.

Western States competitors have to stay focused for the length of the race, which can take up to 30 hours, with elevation gains and losses totaling 41,000 feet and temperatures ranging from below freezing to over 100 degrees. This year was especially tough, thanks to melting snow from El Niño. Trason ran for about 20 miles on ice and at one point tumbled into a crevasse. It's also possible to get lost. Trason's closest female competitor, Corrine Favre of France, took a wrong turn at Mile 78 and was unable to make up the time. "Paying attention for such a long time is difficult," says Jack Raglin, an associate professor of kinesiology at Indiana University who specializes in sports psychology. "The mental fatigue can be overwhelming." Trason agrees. "You get jumpy when you get that tired, and it's nerve-wracking to run in the dark." For both safety and company, many athletes run with a pacer, a volunteer who helps keep them on track. Trason makes sure her pacer is well briefed on professional sports scores. "You get consumed by Western States and forget that there's life beyond the race." Trason also keeps up a running dialogue in her head to keep herself going. "After 50 miles your body just hurts. You have to keep telling yourself that your mind is stronger than your legs."