Youngstedt, S. D., Kripke, D. F., Elliott, J. A., O'Brien, P. M., & Huegel, G. O. (2001). Circadian phase-response curves for exercise and bright light. Medicine and Science in Sports and Exercise, 33(5), Supplement abstract 1009.

Physically active young adults (M = 14; F = 21) and older adults (M = 12; F = 21) were observed over a period of four to five days following a 90-minute "ultra-short" sleep-wake cycle (30-min sleep, 60-min wake). Baseline circadian rhythm was assessed over 30 hours. During the following three days, Ss were exposed to experimental phase-shifting treatments (randomly assigned exercise or bright light), centered at one of eight randomly assigned times around the 24-hour day. Treatments were one hour of treadmill exercise at 60-70% VO2peak, and three hours of bright light.

It was found that exercise had a similar influence on circadian rhythms as did bright light.

Implication. Regular exercise affects the circadian rhythm.

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