Amorim, F. T., Rodriguez, L. O., Oliveira, A., Bonfim, I. P., & Silami-Garcia, E. (2001). Water replacement and kidney function during exercise in a hot humid environment. Medicine and Science in Sports and Exercise, 33(5), Supplement abstract 787.

Males (N = 6) were observed for sweat loss characteristics (urine volume and specific gravity) during pure water replacement while exercising submaximally at three levels, 175, 300, and 500 kcal/h), for two hours. Four thermal conditions were experienced; thermoneutral (18.7 C WBGT) and variations of heat and humidity (25, 27, and 30.5 C WBGT).

Sweat rate increased with higher exercise intensities and hotter environmental conditions. Urine volume was higher than expected in all conditions and highest at the two high-intensity exercise levels in the thermoneutral condition. Urine specific gravity was similar in all conditions.

These results suggest that the water-replacement protocol was overwhelming/excessive because it did not consider inner water resulting from substrate metabolism, fluid vascular redistribution, and substrate mass losses.

Implication. Water that will be produced during exercise should be considered when planning external water replacement procedures.

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