For runners who may compete in hot weather it is critical for performance and safety to develop and maintain heat acclimatization. The human body is able to maintain a fairly constant temperature under varying environmental conditions. To do this, it must be able to gain or lose heat. The core temperature is regulated to remain relatively constant, but the temperature of the shell, the skin and the tissues directly beneath it, varies directly with environmental conditions. The hypothalamus in the brain controls the body temperature and calls into play either heat loss or heat production mechanisms.
Regulation comes in response to changes in the skin or blood temperature.
Normal metabolism in the body produces heat. Increased heat production can come from higher metabolic rates, disease, shivering or exercise. During exercise, the increased metabolic rate and energy production both generate heat. Most of the heat gain is due to the lack of efficiency of the body. Convection - transfer of heat by movement of air or water over the body.