Pahnke, M. D., Trinity, J. D., Trombold, J. R., & Coyle, E. F. (2208). Sodium supplementation maintains serum sodium concentration and improves cognitive function in endurance athletes during exercise. ACSM 55th Annual Meeting Indianapolis. Presentation number 887.

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This study determined the effect of sodium supplementation on serum-Na and cognitive function in endurance athletes with exceptionally high sweat sodium losses. Heat acclimated endurance-trained males (N = 13) with high sweat sodium (sweat-Na) losses (sweat rate x sweat sodium concentration, 106+33mEq/h) cycled a stationary ergometer for three hours at 60% of VO2max in a warm environment (~33.0C). Ss completed two trials, separated by 5-10 days, in which placebo or sodium chloride (18.3+4.7g) was ingested via a capsule to match individual whole body sweat sodium losses, which were determined in a prior preliminary trial. Body mass was maintained during the trials by drinking water with carbohydrate to match fluid losses (e.g. sweat and urine) during exercise. An absorbent patch (10x12cm) was placed on the right forearm, scapula, thigh, and calf for 30 minutes at 30 and 120 minutes of the trial to determine sweat-Na concentration. A subset of subjects (N = 8) completed the Stroop Color-Word Test before and after each trial.

Serum-Na declined significantly during the placebo but not during sodium trial. Body mass did not change in either trial. The rate of sweat-Na losses was similar in both trials. Response time for correct responses to the Stroop Color-Word Test improved from baseline during the sodium trial, but did not change under the placebo condition.

Implication. Serum-Na decreased significantly during three hours of moderate intensity exercise in a warm environment in athletes with high sweat sodium losses when body mass was maintained. There is a suggestion that cognitive function might also be improved.

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