Sims, S. T., van Vliet, L., Cotter, J. D., & Rehrer, N. J. (2004). The effect of sodium loaing on plasma volume and running performance in the heat. Medicine and Science in Sports and Exercise, 36(5), Supplement abstract 574.

Male endurance runners (N = 8) completed two running trials (70% VO2max, 32C, 50% relative humidity) to exhaustion separated by 1 to 3 weeks. Sodium was ingested 2 hours after a standard breakfast in seven portions fed every 10 minutes. A low sodium treatment was 10 meq/l and a high treatment was 164 meq/l. Running commenced 25 minutes after the last sodium ingestion.

Plasma volume and time to exhaustion increased significantly under the high sodium condition.

Implication. Sodium ingestion before running improves endurance performance.

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