Marathons:Going the Distance

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Biology 103

2005 Final Paper

On Serendip

Marathons:Going the Distance

Brom Snyder

26.2 miles, every year hundreds of thousands of people in six continents attempt to run this distance. Running marathons has become popular pastime in the United States, fuelled by the heath and fitness movement sweeping the country, the number of entries continues to grow. The marathon is a test of endurance and to be properly prepared for it one must understand the biology behind the marathon, because running twenty-six miles without that knowledge is a dangerous and potentially fatal proposition.

Having twice attempted to run a marathon ( finishing the first one, dropping out of the second one at mile 18) I have personally experienced "the wall." For me hitting "the wall" meant around mile 21 I started feeling as if my legs had lead weights chained to them, each step an excruciating and exhausting process. "The wall" takes different forms for each individual, sometimes resulting in being unable to feel ones' feet, loss of muscle control, and inability to do some mental processes, forgetting what mile one is on and inability to read watches or calculate pace. (1) In biological terms "the wall" marks the point at which the body has broken down and derived all the energy from the glycogen at its disposal. Glycogen is polymerized form of glucose, a string of glucose molecules. (2) The maximum amount of glucose stored in glycogen for the average person is around 2,000 calories worth. On average, most people burn around 100 calories per mile so by mile 20 all of the available glucose stored in glycogen has been burned and the body is looking for another source of glucose. At this juncture the glucose in fatty acids becomes the source of energy. The process breaking down fatty acids down into usable energy is not as efficient as breaking down glucose, it requires more oxygen than glycogenolysis, thus making the heart work harder delivering the necessary oxygen. (1) (3) As the heart works harder to pump oxygenated blood to the muscles screaming for it, lightheadedness may occur ( the brain is not getting enough oxygen) and various muscle groups do not work as well due to the depletion of glycogen stores.

There are ways to combat hitting "the wall." Many runners "carbo-load" (eating foods rich in carbohydrate days before marathons) in an attempt to maximize the amount of glucose stored in glycogen in the muscles. "Carbo-loading" can be augmented by eating during marathons; most marathons have stations every few miles with power gels (rich in glucose), cookies, and candy. Another strategy utilizes using different sets of muscles, slightly varying the pace and stride length, thereby burning the glycogen in more muscles, allowing the glycogen supplies to last longer. As a runner quickens the pace fast-twitch muscle fibers are utilized. These muscles have not been used as much as slow-twitch muscles in marathons so if a runner is able to use these muscles, they have another source of glycogen, thus holding off the shift to breaking down fat a little longer. (1) (5) Training regimes attempt to acquaint the body with the transfer from the breaking down of glycogen to fat. Repeated exposure to this phenomenon helps runners prepare mentally for when it occurs in the race, forewarned is forearmed. If a runner is willing to put into the miles, between 100-140 miles a week, it can aid the body in adapting to breaking down fat when glycogen supplies are exhausted. (5)

Most runners, and particularly marathoners, fear dehydration. This fear causes many runners( in a study of 488 runners in the Boston Marathon, thirteen percent) to suffer from a condition called hyponatremia. Hyponatremia occurs when too much water is consumed, creating very diluted blood with very low blood sodium levels. In periods of intense exercise the kidneys cannot get rid of the excess water and therefore continuing to drink water results in the dilution of the blood and water moving into cells. If water is moving into cells, these cells swell. If this occurs in the brain, the brain cells will expand pressing against the skull, compressing the brain stem, thereby preventing the performance of vital functions like breathing, possibly causing death. This problem is more prevalent as number of marathon entrants rises. Most of these new entrants are not world class athletes, taking more than four hours to finish the race. The length of time they are running, the frequency of water stations, and fear of hydration all contribute to many suffering from hyponatremia. (1) (4)

There are factors beyond training and knowledge of running which can affect performance in events like the marathon. At the most elite levels of distance running, East Africans, particularly the Kenyans and Ethiopians dominate. The Kalenjins, a tribe in Kenya of 500,000, "win 40 percent of top international distance running honors...three times as many distance medals as athletes from any other nation in the world." (6) While environmental factors, like elevation (the higher the elevation the less oxygen available so one's body conditions itself to deal with situations where oxygen is less available, like during a race), affect the development of athletes; the Kalenjins' dominance points to factors beyond environmental. If it was just a matter of training at higher elevation American athletes could all train in Colorado and be competitive internationally. In laboratory tests where Kenyan runners were compared with Scandinavians, another group which at one point dominated distance running, the Kenyans' muscle fibers contained more mitochondria (where the glucose combines with oxygen resulting in energy) and capillaries. (6) The greater number of capillaries means more oxygen is delivered to the mitochondria and more energy is produced. With more mitochondria and capillaries than the Scandinavians, the Kenyans are more efficient, with each breath resulting in a greater production of energy. Anyone can have an increased number of capillaries and mitochondria but this trait seems to appear more frequently in East African black populations, particularly those of the Kalenjin tribe. While having the right genes does not make an elite distance runner, having the genetic predisposition for more efficient aerobic exercise, like the Kalenjins apparently do certainly helps.

Biology helps us prepare and succeed in running marathons but there are factors beyond biology's current scope that affect one's ability to run a marathon. Where does the desire to put one's self through 26.2 miles of excruciating physical exertion come from? From a biological perspective one is depleting one's body's energy to frighteningly low levels and weakening one's immune system for no discernible benefit. The question of why humans do things like run marathons, is their a deep-seeded undiscovered biological need to do so, are the questions biology must tackle as it moves into the 21st century,

1)marathon and beyond, COMMENTS ABOUT IT Sara Latta, " Hitting 'the Wall'" 2003

2) Kimball's Biology Pages "Glycogen" ,


4)New York Times , Gina Kolata "Study Cautions Runners to Limit Their Water Intake"

5) Boston Globe, Judy Foreman "Is there a limit to how fast, long someone can run?" April 13, 2004

6) Run-Down , Jon Entine "Shattering Racist Myths: The Science Behind Why Kenyans Dominate Distance Running"

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