Baylies, J. L., Philllips, M. D., Mercer, S. P., Mitchell, J. B., & Hugues, A. M. (1997). Interaction between volume and sodium content: Effects on post-exercise rehydration and cardiovascular function. Medicine and Science in Sports and Exercise, 29(5), Supplement abstract 768.

The interaction between sodium content and volume of fluid ingested on post-exercise rehydration and the effect of rehydration of cardiovascular function was examined.

Males (N = 10) completed four trials (60% VO2max for 90 min) in a warm environment (35 degrees Celsius) until dehydration caused a body weight loss of 2.9%. This was followed by 180 min of resting rehydration followed by an additional 20 min of exercise (to assess cardiovascular function). During rehydration, one of four fluids was ingested:

1. low volume (100% fluid replacement), low sodium (25 mM);
2. low volume, high sodium (50 mM),
3. high volume (150% fluid replacement), low sodium, and
4. high volume, high sodium.

Thirty percent of the fluid was initially ingested, the remainder following in 5 equal feedings every 30 min.

Dehydration altered cardiovascular function. High volume fluid produced significantly greater rehydration than the low volume conditions. The degree of rehydration did not influence the recovery of cardiovascular function. Sodium concentration had no differential effect.

Implication. Rehydration is achieved better by ingesting more fluid than that which is lost in exercise. However, this does not influence the recovery of the cardiovascular system.

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