Maxwell, N. S., Gardner, F., & Nimmo, M. A. (1999). Intermittent running: Muscle metabolism in the heat and effect of hypohydration [fluid loss]. Medicine and Science in Sports and Exercise, 31, 675-683.

Two studies evaluating the cause of performance deterioration in hypohydrated conditions were conducted. Treadmill running involving repeated 20-second runs of increasing velocity, separated by 100-seconds of rest, were performed in hot-humid (32.8 degrees Celsius, 80% relative humidity) and cooler (21.3 degrees Celsius, 50 % relative humidity) conditions.

Performance was reduced in the hot-humid conditions and further affected by fluid loss.

Implication. Reduced intermittent running performance in the heat is not caused by greater muscle glycogenolysis or lactate accumulation. Fluid loss itself is the principal cause of performance deterioration.

Return to Table of Contents for this issue.