During strenuous exercise the body's heat production may exceed 1000 W. Some of the heat produced is stored, raising body core temperature by a few degrees. Rises in body temperature are sensed by central and skin thermoreceptors and this sensory information is processed by the hypothalamus to trigger appropriate effector responses. Other sensory inputs from baroreceptors and osmoreceptors can modify these responses. Evaporation of sweat and increased skin blood flow are effective mechanisms for the dissipation of heat from the body but dehydration impairs the capacity to sweat and lose body heat. Hot, humid environments or inappropriate clothing may compromise the ability to lose heat from the body. Exercise training improves tolerance to exercise in the heat by increasing the sensitivity of the sweat rate/core temperature relationship, decreasing the core temperature threshold for sweating and increasing total blood volume.