Hecker, A. L., & Wheeler, K. B. (1994). Impact of hydration and energy intake on performance. The Journal of the National Athletic Trainers Association, 19, 4-9.

Even moderate levels of dehydration can compromise physical performance. The body attempts to conserve water during exercise by reducing the amount of urine produced. Heat acclimated individuals may have sweat rates in excess of 3.5 quarts per hour.

After significant dehydration (2+%), such as that experienced to "make weight," it takes considerable time to rehydrate. For example, if 4% of body weight is lost as fluid, after five hours of rehydration, performance potential (muscle and aerobic endurance) still will not have recovered.

Dehydration affects power, aerobic and anaerobic parameters, and cognitive functioning. In rifle marksmen, accuracy and detection of cues have been shown to be decreased by between 15-20% of normal.

Thirst alone is not a good indicator of fluid need. Prevention of dehydration during work in the heat requires scheduled fluid intakes.

Affects of dehydration on performance. If water loss is defined as a percentage of body weight loss, the following progressive deteriorations in performance should be expected.

• 0-2%. Impaired thermoregulatory ability.
• 2-3%. Reduced muscular endurance time.
• 3-6%. Reduced muscular strength, reduced endurance time, heat cramps.
• 6+%. Severe heat cramps, heat exhaustion, heat stroke, coma, death.

Implication. Serious attention to fluid replacement on a scheduled basis is required for all sports that induce considerable sweating and/or are performed in hot humid conditions.

Return to Table of Contents for this issue.