Regulatory, Integrative and Comparative Physiology

Exercise elicits phase shifts and acute alterations of melatonin that vary with circadian phase

Orfeu M. Buxton, Calvin W. Lee, Mireille L'Hermite-Balériaux, Fred W. Turek, Eve Van Cauter


To examine the immediate phase-shifting effects of high-intensity exercise of a practical duration (1 h) on human circadian phase, five groups of healthy men 20–30 yr of age participated in studies involving no exercise or exposure to morning, afternoon, evening, or nocturnal exercise. Except during scheduled sleep/dark and exercise periods, subjects remained under modified constant routine conditions allowing a sleep period and including constant posture, knowledge of clock time, and exposure to dim light intensities averaging (±SD) 42 ± 19 lx. The nocturnal onset of plasma melatonin secretion was used as a marker of circadian phase. A phase response curve was used to summarize the phase-shifting effects of exercise as a function of the timing of exercise. A significant effect of time of day on circadian phase shifts was observed (P < 0.004). Over the interval from the melatonin onset before exercise to the first onset after exercise, circadian phase was significantly advanced in the evening exercise group by 30 ± 15 min (SE) compared with the phase delays observed in the no-exercise group (−25 ± 14 min, P < 0.05). Phase shifts in response to evening exercise exposure were attenuated on the second day after exercise exposure and no longer significantly different from phase shifts observed in the absence of exercise. Unanticipated transient elevations of melatonin levels were observed in response to nocturnal exercise and in some evening exercise subjects. Taken together with the results from previous studies in humans and diurnal rodents, the current results suggest that1) a longer duration of exercise exposure and/or repeated daily exposure to exercise may be necessary for reliable phase-shifting of the human circadian system and that 2) early evening exercise of high intensity may induce phase advances relevant for nonphotic entrainment of the human circadian system.

  • jet lag
  • shift work


  • This work was supported by grants from the Air Force Office of Scientific Research (F49620–96–1-0252 and F49620–98–1-0028), the Department of Defense (Augmentation Award for Science and Engineering Research Training F49620–96–1-0252), the National Heart, Lung, and Blood Institute of the National Institutes of Health (NIH) (Sleep Research Training Grant T32-HL07909), and the National Sleep Foundation (Pickwick Fellowship). The University of Chicago Clinical Research Center is supported by NIH Grant PHS M01 RR-00055.

  • Address for reprint requests and other correspondence: O. M. Buxton, Dept. of Medicine, MC 1027, Univ. of Chicago, 5841 S. Maryland Ave., Chicago, IL 60637 (E-mail:orfeu{at}

  • The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

  • 10.1152/ajpregu.00355.2002

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