There are few stresses to which the body is exposed that even nearly approach the extreme stresses of heavy exercise. In fact, if some of the extremes of exercise were continued for even moderately prolonged periods, they might be lethal. Therefore, in the main, sports physiology is a discussion of the ultimate limits to which several of the bodily mechanisms can be stressed. To give one simple example: In a person who has extremely high fever approaching the level of lethality, the body metabolism increases to about 100 per cent above normal. By compari-son, the metabolism of the body during a marathon race may increase to 2000 per cent above normal.
Female and Male Athletes Most of the quantitative data that are given for the young male athlete, not because it is desirable to know only these values but because it is only in male athletes that relatively complete measurements have been made. However, for those measurements that have been made in the female athlete, almost identical basic physiologic principles apply, except for quantitative differences caused by differences in body size, body composition, and the presence or absence of the male sex hormone testosterone.
In general, most quantitative values for women—such as muscle strength, pul-monary ventilation, and cardiac output, all of which are related mainly to the muscle mass—vary between two thirds and three quarters of the values recorded in men. When measured in terms of strength per square centimeter of cross-sectional area, the female muscle can achieve almost exactly the same maximal force of contrac-tion as that of the male-between 3 and 4 kg/cm2. Therefore, most of the difference in total muscle performance lies in the extra percentage of the male body that is muscle, caused by endocrine differences that we discuss later.
The performance capabilities of the female versus the male athlete are illustrated by the relative running speeds for a marathon race. In a recent comparison, the top female performer had a running speed that was 11 per cent less than that of the top male performer. For other events, however, women have at times held records faster than men—for instance, for the two-way swim across the English Channel, where the availability of extra fat seems to be an advantage for heat insulation, buoyancy, and extra long-term energy.
Testosterone secreted by the male testes has a powerful anabolic effect in causinggreatly increased deposition of protein everywhere in the body, but especially in the muscles. In fact, even a male who participates in very little sports activity but who nevertheless is well endowed with testosterone will have muscles that grow about 40 per cent larger than those of a comparable female without the testosterone.
The female sex hormone estrogen probably also accounts for some of the differ-ence between female and male performance, although not nearly so much as testos-terone. Estrogen is known to increase the deposition of fat in the female, especially in the breasts, hips, and subcutaneous tissue. At least partly for this reason, the average nonathletic female has about 27 per cent body fat composition, in contrast to the nonathletic male, who has about 15 per cent. This is a detriment to the highest levels of athletic performance in those events in which performance depends on speed or on ratio of total body muscle strength to body weight.
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