Hill, D. W., Borden, D. O., Darnaby, W. M., Hendricks, D. N., & Hill, C. M. (1992). Effect of time of day on aerobic and anaerobic responses to high-intensity exercise. Canadian Journal of Sport Sciences, 17, 316-319.

Men (N = 8) and women (N = 6) performed all-out cycle ergometer tests in the morning and afternoon in randomized order. Work rate was a constant 5 W/kg for females and 6 W/kg for males.

Total work performed was 9.6% greater in the afternoon compared to the morning. Aerobic work improved 5.1% and anaerobic work 5.6% in the afternoon. There were no gender differences.

Implication. The capacity to perform exercise work is higher in the afternoon than in the morning.

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