PHASE-SHIFTING HUMAN CIRCADIAN-RHYTHMS WITH EXERCISE DURING THE NIGHT-SHIFT

Appropriately timed exercise can phase shift the circadian rhythms of rodents. The purpose of this study was to determine whether exercise d uring the night shift could phase delay the temperature rhythm of huma ns to align with a daytime sleep schedule. Exercise subjects (N = 8) r ode a stationary cycle ergometer for 15 min every h during the first 3 of 8 consecutive night shifts, whereas control subjects (N = 8) remai ned sedentary. All subjects wore dark welder's goggles when outside af ter the night shift until bedtime, and then slept in dark bedrooms. Sl eep was delayed 9 h from baseline. Rectal temperature was continuously measured. There were fewer evening-types and more morning-types in th e exercise group than in the control group, which should have made pha se delay shifts more difficult for the exercise group. Nevertheless, a majority of the exercise subjects (63%) had large temperature rhythm phase delay shifts (> 6 h in the last 4 days relative to baseline), wh ereas only 38% of the control subjects had large shifts. An ANCOVA sho wed that, when morningness-eveningness was accounted for (as the covar iate), the exercise group had a significantly larger temperature rhyth m phase shift than the control group. As expected, there was a correla tion between the temperature rhythm phase shift and morningness-evenin gness in the control group, with greater eveningness resulting in larg er phase shifts. However, there was no such relationship in the exerci se group; exercise facilitated temperature rhythm phase shifts regardl ess of circadian type. These results suggest that exercise might be us ed to promote circadian adaptation to night shift work.