Control of Body Temperature During Exercise
“Oh, everybody was affected by the heat [in the 1956 Olympic Marathon in Melbourne]. I think that 13 boys were carried from the route on stretchers. We all knew that the heat would not agree with us; in fact, the great Zatopec, just before the race, looked up at the sun in the sky and said, (Today, we all die.9 99
Yet, I repeat, these symptoms, however unpleas-ant and alarming have no baleful significance as of danger. One recalls the historic Marathon race in London in 1908 when the Italian, Dorando, staggered blindly disorientated into the Stadium and fell, lying, according to picturesque journalistic phraseology, for a time between life and death. Yet by the following morning he had completely recovered and subsequently ran a considerable number of Marathon races.
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“At that time biochemistry was in its infancy; modern researchers have made us familiar with the true significance of these symptoms and have taught us to transfer the lesion from the heart, about which solicitude is mistakenly expressed, to less vital structures.99
The runner faces a major problem: the excess heat produced by muscle contraction. Humans are homeotherms, and to live they must keep their body temperatures within a narrow range (35 to 42 °C) despite wide variations in environmental temperatures and differences in levels of physical activity.
During exercise, however, the conversion of chemical energy stored in ATP into mechanical energy is extremely inefficient, so that as much as 70% of the total chemical energy used during muscular contraction is released as heat rather than as athletic endeavor.
Thus, when Bruce Fordyce or Don Ritchie (see post 8) wins an ultramarathon at an average pace of 16.3 km/hr, he utilizes about 56 kJ of energy every minute (see Exercises 4.1, a and b) or about 18,480 kJ in the 5-1/2 hours that he runs. Of this, only 5,940 kJ help transport the athlete from the start to the finish of the race; the remaining 12,540 kJ are nothing more than a hindrance, as they serve only to heat the athlete. Were the athlete unable to lose less than one tenth (1,115 kJ) of that heat, his body temperature would rise above 43 °C, causing heatstroke.
To prevent disastrous overheating and heatstroke and to control the increased heat associated with exercise, the body must be able to call upon a number of very effective heat-losing mechanisms.