Normally, the body maintains its internal temperature on hot days by sweating - up to 1 liter per hour. When strenuous activity is involved, the rate of sweat production can increase to as much as 3 liters per hour. It is easy to see why fluid replacement is an important method of preventing heat-related emergencies. When the body sweats, important salts are also eliminated from the body. The body's need for water is only second in importance to its need for oxygen.
Aerobic exercise involves the generation of internal heat through performance of muscular work.
Heat is lost principally through evaporation of sweat from the body's surface, which cools the individual at the price of losing vital circulating fluids. Prolonged strenuous exercise invariably leads to dehydration, which may lead to headaches, muscle cramps, lightheadedness, fatigue, confusion, lethargy, and persistent elevated body temperature. Advanced stages of heat exhaustion from exercise may lead to coma and even cardiac arrhythmia's and sudden death. Drink before, during, and after exercise and don't rely on your thirst mechanism to tell you how much fluid you need. The following are actions to be taken to help prevent dehydration and hyperthermia during exercise.