Exercise and Core Temperature.
Abstract
In humans the most important responses for removing heat from the body are sweating, which increases heat loss by evaporation, and cutaneous vasodilation, which increases skin blood flow and heat transfer from core to skin. Vigorous exercise can increase heat production within the body ten-fold or more. During the first few minutes of exercise, most of the heat produced is retained within the body, raising core temperature until it elicits heat-dissipating responses sufficient to eliminate heat as fast as it is produced. The steady-state increase in core temperature is proportional to the rate of heat production and, within certain limits, independent of environmental conditions. Because of the levels of skin blood flow needed for high rates of heat dissipation in a hot environment, exercise and heat dissipation make competing demands on the cardiovascular system. Moreover, if water and electrolytes lost as sweat are not replaced, plasma volume eventually is depleted, thus reducing central blood volume and impairing cardiac filling. Through these mechanisms, secondary effects of the thermoregulatory responses contribute to many of the adverse effects of heat stress, though other mechanisms related to high core temperature also have a role, especially in heat stroke. Heat tolerance is increased by aerobic exercise conditioning and by acclimatization to heat. Conversely, poor physical fitness and certain disease states and drugs are associated with impairment of the thermoregulatory responses. The foregoing factors account for most of the inter-individual differences in heat tolerance associated with gender and age. Because of the high rates of heat production, heat-related illnesses are much more likely during exercise than is hypothermia. However, hypothermia may occur during prolonged exercise due to inadequate clothing, changes in the weather, or fatigue or musculoskeletal injury which reduces the level of exercise that can be sustained.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1999
- Accession Number
- ADA377492
Entities
People
- C. B. Wenger
Organizations
- United States Army Research Institute of Environmental Medicine