The loss of body fluids inevitably leads to a decrease in performance, especially when training in hot environments. Therefore, all individuals who exercise, train, and/or compete are advised to rehydrate and replace fluids and electrolytes lost during exercise, especially through sweating. Maintaining adequate hydration is not only a physiological necessity, but it also contributes to a performance advantage and reduces the risk of medical problems or injury due to fluid loss.

Prevent your body from overheating 

The water and electrolyte balance is crucial for thermoregulation and performance in the heat. When exercising in the heat, water and electrolytes are lost through sweating. During exercise, sweat production often exceeds water intake, resulting in a water deficit or hypohydration. The water deficit decreases both intracellular and extracellular fluid volume. It also leads to plasma hypertonicity and plasma hypovolemia, both of which negatively affect heat loss. So proper rehydration prevents your body from overheating.