Phase-Shifting Effect of Light and Activity on the Human Circadian Clock.
Annual technical rept. 1 Mar 1990-28 Feb 1991,
CHICAGO UNIV IL DEPT OF MEDICINE
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To determine whether single presentation of light or physical activity can phase shift the human circadian clock, 8 young male subjects were subjected to the following experimental protocol. Following entrainment to a fixed sleep wake and light-dark cycle for one week, each subject underwent 3 separate studies one baseline study in which measurements of circadian phase positions were performed under constant routine conditions i.e. constant wakefulness in recumbent position under constant dim light with constant caloric intake for 42 hrs, and two studies in which each subject was exposed to a 3-h session of either bright light 5000 Lux or physical activity exercise on a stationary arm-and-leg exerciser during the constant routine regimen. In order to estimate accurately circadian phase positions, 8 overt rhythms were monitored in each subject plasma cortisol, plasma TSH, plasma melatonin, plasma glucose, plasma C-peptide, core temperature, total activity and mental performance. The immediate phase shifting effects of bright light or exercise were measured on the monitored rhythms on the first day following stimulus presentation. Preliminary analysis of currently available data indicate that both light and exercise resulted in a phase advance of approximately one hour.
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