title: Intermittent bright light and exercise to entrain human circadian rhythms to night work.
abstract: Bright light can phase shift human circadian rhythms, and recent studies have suggested that exercise can also produce phase shifts in humans. However, few studies have examined the phase-shifting effects of intermittent bright light, exercise, or the combination. This simulated night work field study included eight consecutive night shifts followed by daytime sleep/dark periods (delayed 9 h from baseline). There were 33 subjects in a 2 x 2 design that compared 1) intermittent bright light (6 pulses, 40-min long each, at 5,000 lx) versus dim light and 2) intermittent exercise (6 bouts, 15-min long each, at 50-60% of maximum heart rate) versus no exercise. Bright light and exercise occurred during the first 6 h of the first three night shifts. The circadian phase marker was the demasked rectal temperature minimum. Intermittent bright-light groups had significantly larger phase delays than dim-light groups, and 94% of subjects who received bright light had phase shifts large enough for the temperature minimum to reach daytime sleep. Exercise did not affect phase shifts; neither facilitating nor inhibiting phase shifts produced by bright light.
authors.affiliation: Biological Rhythms Research Lab, Department of Psychology, Rush-Presbyterian-St. Luke's Medical Center, Chicago, Illinois 60612, USA.
authors.forename: E K
authors.initials: EK
authors.lastname: Baehr
authors.forename: L F
authors.initials: LF
authors.lastname: Fogg
authors.forename: C I
authors.initials: CI
authors.lastname: Eastman
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000328:Adult; D002940:Circadian Rhythm / Q000502:physiology*; D003624:Darkness; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008027:Light; D008029:Lighting; D008297:Male; D017440:Photoperiod; D010789:Phototherapy; D012890:Sleep / Q000502:physiology; D014940:Work Schedule Tolerance / Q000502:physiology*