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During physical exercise, the production of heat in the working skeletal muscles increases tremendously, inducing an increase in core temperature, which can increase for up to two degrees or more. Thermoregulatory reflexes are activated to eliminate excess heat to the environment. Thermal balance is maintained by a combination of physical and physiological mechanisms similar to those in resting conditions but with a few important differences. During exercise, the cardiovascular system is subjected to opposing thermoregulatory and nonthermoregulatory responses, where the latter increase the blood flow through the working skeletal muscles and maintain appropriate blood pressure and the former increase skin blood flow to eliminte heat. The temperature threshold to induce vasodilation in the skin and sweating is increased and the sensitivity of the responses for heat elimination is changed, which is represented by the skin blood flow rate of change as a function of internal temperature. In addition, the maximal skin blood flow is lowered. The main mechanisms for heat elimination are increased skin blood flow due to increased vascular conductance and sweating, along with increased convective heat transfer in the body due to increased cardiac output. Prolonged sweating results in the loss of electrolytes and water that need to be appropriately replaced. Furthermore, high intensity exercise in extremely hot and humid environment can lead to hyperthermia, hypovolemia and shock. Professional athletes develop mechanisms that enable more optimal heat elimination during exercise.