Thermoregulation and clinical disorders associated with exercise and heat stress

An inevitable consequence of intense or prolonged exercise is hyperthermia. Skeletal muscles that are working at maximum intensity can increase their energy consumption by as much as 60-fold; the Gore temperature of the body increases because much of this energy is converted to heat, which is transferred from muscle to blood. If ambient temperature and relative humidity are high, the capacity for heat loss Is severely limited and prolonged exercise produces severe hyperthermia and impaired athletic performance. There also is increased risk of such heat-induced illnesses as muscle cramps, rhabdomyolysis, heat exhaustion, and heatstroke, Despite an awareness of the harmful effects of hyperthermia on health and exercise performance, equestrian events are commonly held in hot climates, which challenge the body's capacity for temperature regulation and maintenance of fluid balance. There is concern about the ability of horses to safely complete the speed-and-endurance test of the 1996 Olympic Three-Day Event to held in Atlanta, Georgia, where the prevailing conditions are likely to be hot and humid. Average maximum temperatures for this city in July and August are 31 degrees to 34 degrees C (88 degrees to 94 degrees F), with relative in humidity ranging from 60% to 80%. This article reviews the physiology of thermoregulation in horses during exercise and the clinical disorders that are associated with exercise-induced hyperthermia.