PRELIMINARY STUDIES ON THE IMMEDIATE PHASE-SHIFTING EFFECTS OF LIGHT AND EXERCISE ON THE HUMAN CIRCADIAN CLOCK

The aim of the present research was to determine the magnitude and dir ection of immediate phase shifts of human rhythms following a single e xposure to a 3-hr pulse of bright light or physical activity. The puls e of light or activity was presented under ''constant-routine'' condit ions, and measurements of the resultant phase shifts were performed un der the same constant-routine conditions on the first day following pu lse presentation. Four overt rhythms that are strongly dependent on ci rcadian timing-namely, the rhythms of plasma cortisol, plasma thyroid- stimulating hormone (TSH), plasma melatonin, and body temperature-were monitored. The analysis of the TSH profiles indicated that exposure t o light at about the time of the minimum of body temperature resulted in phase advances averaging less than 1 hr in magnitude. Exposure to l ight approximately 3 hr before the time of the minimum of body tempera ture resulted in phase delays of 1-2 hr. Preliminary analyses of the m elatonin profiles have confirmed these observations. Our findings rega rding the effects of exercise are still inconclusive.