. "6. Energetics and Climate with Emphasis on Heat: A Historical Perspective." Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations. Washington, DC: The National Academies Press, 1993.
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Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations
ments are qualitatively similar in hot and temperate areas but may remain quantitatively lessened in tropical climates by the sustained high loss of sweat and anorexia.
The question of whether heat acclimatization (outdoors or in the field) or acclimation (indoors or in laboratories) has an effect on metabolic rate during rest and exercise has been studied intensively with mixed results. Some pertinent studies are cited from among the many in the literature.
Robinson et al. (1945) and Eichna et al. (1950) found that heat acclimation lowered the metabolic rate associated with exercise in the heat by 4 to 8 percent. Shvartz et al. (1977) studied, using cycle ergometry, several groups of men who varied widely in physical fitness and were exposed to 8 days of heat acclimation. Despite interindividual differences in physical fitness, the postacclimation oxygen uptakes were invariably slightly less in all of the environments studied including a 39.4°C (103°F) environment (see Table 6-8).
Sawka et al. (1983) reevaluated the problem. They concluded that heat acclimation, if it had an effect at all, slightly lowered metabolism associated with performance of exercise in the heat. The conclusion was based not only on their studies of 42 subjects of both genders, but on a review of the literature as well. Young et al. (1985) arrived at essentially the same conclusion (see Table 6-12).
Presumably, the small reduction in metabolism is caused by the lesser respiratory and cardiac work caused by more efficient evaporative cooling, peripheral circulation, regulation, and the lowering of body temperature, although as Sawka et al. (1983) have pointed out, the role of such factors is
TABLE 6-12 Statistical Analysis for Comparison of Main Effects of Heat Acclimation and Environment on Respiratory Measurements of Young Men (n = 13)