McConell, G. K., Stephens, t. J., & Canny, B. T. (1999). Fluid ingestion does not influence intense 1-h exercise performance in a mild environment. Medicine and Science in Sports and Exercise, 31, 386-392.

Well-trained males (N = 8) cycled for 45 min at ~80% VO2max, followed by a 15-min "all-out" performance ride, in a mild environment under three conditions: no fluid, receiving a volume of water that prevented body mass loss, or receiving 50% of the fluid volume. Despite some differences in body mass loss, fluid ingestion did not differentially affect heart rate, rectal temperature, plasma volume, plasma sodium or potassium, RPE, or work completed in the 15-min ride.

Implication. Little benefit is gained by drinking water during one-hour of exercise in a mild environment.

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