Pahnke, M. D., Trinity, J. D., & Coyle, E. F. (2006). Large interindividual variability in sweat sodium loss in well-trained endurance athletes. Medicine and Science in Sports and Exercise, 38(5), Supplement abstract 1509.

This study determined the variability in sweating rate and sweat sodium concentration in endurance athletes during exercise. Heat-acclimatized athletes (M = 84; F = 48) cycled a stationary ergometer for 30 minutes at 70-75% of maximum heart rate, following an 8-minute warm-up. Sweat rate was calculated from the change in body weight. An absorbent patch (10 x 12 cm) was placed on the right forearm and scapula for sweat collection during the 30 min trial. Trials were performed in a warm environment (30.1 + 2.8°C dry bulb; 60.6±8.5% relative humidity) and Ss were fan cooled (3.5 + 0.4 m/s).

Absolute sweating rate was 1.4±0.5 L/hr with a coefficient of variation (CV) of 33.8%. Between-subject variability was similar when adjusted for body weight. Calculated sodium loss exhibited high variability (CV = 61.1%).

Implication. There is large variation in both the sweating rate and sweat sodium concentration of endurance athletes.

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