Dehydration – An abnormal loss of water from the body, especially from illness or physical exertion.

Counteracting Dehydration

Dehydration greater than 2% of body mass decreases aerobic exercise performance in temperate, warm, and hot environments; and as your level of dehydration increases, aerobic exercise performance is reduced proportionally. Acute dehydration will effect performance regardless of whole body hyperthermia or the environmental temperature. However, your time to exhaustion is quicker in hot environments than in cold ones. 

Everyone is different and sweats at different rates, so fluid replacement under identical conditions can be different for each individual. The best way to determine sweat rate is to measure your body weight before and after exercise. Active individuals  should drink at least 1 pint of fluid for each pound of body weight lost. Meals can also help stimulate thirst resulting in fluid balance restoration. Snack breaks during long training sessions can help you replenish fluids and be important in replacing sodium and other electrolytes. The color of your urine can be a simple and inexpensive way to determine adequate hydration; the darker yellow/brown your urine color is the greater degree of dehydration, paler color urine indicates adequate hydration. 

Over Drinking

Over drinking fluids is the mechanism that leads to hyponatremia (water intoxication). Hyponatremia is the consumption of excess water during strenuous exercise, without the adequate replacement of sodium. Sodium is essential for fluid balance, regulation of blood pressure, and a normal functioning nervous system. This can all be prevented simply by not drinking in excess of sweat rate and by consuming salt-containing fluids or foods when participating in exercise events that result in continuous sweating.