This is an excerpt from Running by Joseph A. PuleoP & atrick Milroy.
Physiology of Runners
As more nations entered competition, ethnic variations in ability appeared. Afro-Caribbean athletes showed themselves to be the preeminent sprinters, whereas those from higher altitudes became the fastest endurance athletes, their bodies having adapted to a decreased oxygen concentration in inhaled air. The act of sprinting fast uses nearly all the muscles of the body during the event. A still photograph of the top exponents at full speed will show taut neck muscles and bulging eyeballs, not exactly the first areas to be considered when running! But if these muscles, in whatever small way, are used to increase speed, then these muscles must be trained for the event in exactly the same way as the massive thighs that provide the explosive power and high knee lift more usually associated with sprinting. Conversely, the best long-distance runners became almost pitifully thin, especially in the largely underused upper limbs, as it was realized that the less weight that they carried, the less energy would be expended in moving their bodies efficiently for mile after mile. However, one enemy of the distance runner is dehydration, a catalyst for both illness and injury, so adaptation to conserve and absorb water, especially in warmer climates, was at odds with the perceived need to be emaciated. Low fat stores, thin and sinewy muscles, and a low mass of other soft body tissues are not conducive to transporting large volumes of fluid internally during a run. The core temperature of the body needs to remain as close as possible to 98.6 degrees F (37 degrees C), not only to work most efficiently, but also, and more important, to survive. The energy burned when running produces heat, and it is by the mechanism of sweating that the core temperature is maintained. If the body is dehydrated, this cannot occur, so at worst a life-threatening hyperthermia may develop as the body temperature rapidly soars. This may help to explain why some winners of distance races can be comparatively well built, because they are able to store larger quantities of fluid to provide for the event. Science shows that performance deteriorates precipitously as the runner becomes overheated and dehydrated, so as with the tortoise and the hare, the winner may be the runner who has prepared best for the whole distance and not relied on pure speed to win the day.
Transposing the body types and events quickly demonstrates the impracticality of either entering the other’s competition. The sprinter would quickly tire as he carried his comparatively heavy body for more than a few hundred meters, even if he could store sufficient fluid, whereas the undermuscled distance runner would immediately be at a disadvantage in an event requiring brute strength and power. These are extreme examples, but in general most events attract successful competitors who have comparatively similar physiques. It is interesting to consider how rare it is that more than one world record is held by a single competitor; where it is, the events tend to require very similar speeds and skills. Thus, Michael Johnson simultaneously held the 200- and 400-meter records, and Haile Gebrselassie the 5K and 10K, but for success at the highest level, the Olympics and world championships, very few runners enjoy the luxury of being able to prepare for, let alone win, more than one event.
Women have been latecomers to the running scene. Races for women longer than 400 meters were not introduced to the Olympic Games until 1964 because it was considered, without any scientific proof, that they might suffer some unspoken medical ailment if they were to “strain” themselves. Once it was shown that they thrived in competition, their advancement was so rapid that by 1984 they were allowed their very own marathon at the Los Angeles Olympics. Anatomically, women are generally disadvantaged compared to their male counterparts, especially where the long, light levers that make up the lower limbs are concerned, but physiologically they are in some ways better prepared, especially for ultradistance running. Because they have proportionately more fat as a percentage of body weight compared to their male counterparts, they have greater reserves of energy and stored fluid to call on, although it may take days rather than hours of competition for this to emerge. It is in ultradistance racing that the performance of women comes closest to men. With increasing distance, the difference between the sexes in statistical terms in time run becomes less and less marked, so it may well be that one day a woman will win an open race purely as a result of better physiological efficiency. Women are disadvantaged by relatively short thighs, which become exaggerated by their wider hips and bring the pelvis closer to the ground, resulting in a reduction of stride length. Stride length is perhaps the factor with the most effect on the speed of running. Although the fastest runners take no more than double the number of strides of the slowest over a given unit of time, their stride length may be up to four times greater.
Although the abdomen of the male largely consists of the intestinal organs, which are involved in fluid balance and retention, that of the woman also has to accommodate the relatively bulky uterus and reproductive organs, limiting the volume available for the bowels. These are not large differences, perhaps even only 1 percent or 2 percent, but they also determine the differences between the relative athletic performances of the two sexes. Add to that breasts and the limitation of smaller chests and lung capacity, as well as smaller feet, which mean that part of the mechanical leverage of propulsion is reduced, further handicapping women when pure speed is the consideration. However, as the male distance runners have shown, small size is not necessarily a disadvantage, and the physiological differences that become more marked in favor of women with greater time and distance run may ultimately lead to an equalization between the sexes over the longest distances.
Once the genetic core of the body has been established, there is only so much that each individual can do to develop his or her physique as a running machine. Even if one discounts artificial aids to body shaping, such as liposuction or steroid drugs, there are certain limits to the adaptation of the adult human form. No mature adult can lose or gain height voluntarily, and exercise training and dieting will only change or mature physique within the limits of capacity, such that although muscles develop as a result of exercise, there are individual limits to the amount of exercise that any single person can tolerate. So the 280-pounder, whose previous leisure activities had been purely nutritional, can expect to reduce his weight and change his shape by exercising to develop a runner’s physique. However, skin has limits both to elasticity and in its ability to retract once overstretched, so the excess will remain visible however assiduously that individual maintains the training program.
This is an excerpt from Running Anatomy.