Fluid Replacement and Heat Stress, 1993
Pp. 85-97. Washington, D.C.
National Academy Press
Michael N. Sawka1 and P. Darrell Neufer
During muscular exercise, the magnitude of core temperature elevation is proportional to the metabolic rate and somewhat independent of the environmental condition (Nielsen, 1938). The elevation of the core temperature represents the storage of metabolic heat, which is a by-product of skeletal muscle contraction. At the initiation of exercise, the metabolic rate increases immediately; however, the thermoregulatory effector responses respond more slowly. The thermoregulatory effector responses, which enable dry and evaporative heat loss to occur, increase in proportion to the rate of heat production (Nielsen, 1966). Eventually, these heat loss mechanisms increase sufficiently to balance metabolic heat production, allowing a steady-state core temperature to be achieved.
An individual's aerobic fitness (Armstrong and Pandolf, 1988), acclimatization state (Wenger, 1988), and hydration level (Sawka, 1988) have
Michael N. Sawka, U.S. Army Research Institute of Environmental Medicine, Natick, MA 01760