Youngstedt, S. D., Kline, C. E., Zielinski, M. R., Moore, T. A., & Elliott, J. A. (2006). Circadian phase-shifting effects of bright light vs. exercise and bright light and exercise combined. Medicine and Science in Sports and Exercise, 38(5), Supplement abstract 1005.

This study compared the phase-shifting effects of bright light alone vs. exercise alone (of equivalent durations) vs. bright light plus exercise. Adults (N = 6) completed each of three 2.5-day treatments in counterbalanced order. During each treatment, Ss followed a 180-minute ultra-short sleep-wake cycle, which involved sleeping in darkness for 1-hour intervals, followed by staying awake in dim light for 2-hour intervals, repeated throughout each treatment. Urine was collected every 90 minutes and analyzed. During each treatment, baseline acrophase of 6-sulphatoxymelatonin (aMT6s) (24-hr peak) was assessed from samples collected during the first 24 hours in the laboratory. The phase-shifting stimuli were administered on the second night of each treatment. Ss received 1) bright light (5,000 lux) from 10:10-11:40 pm; 2) exercise (running at 70% max) from 10:10-11:40 pm; or (3) bright light (10:10-11:40 pm), followed by exercise from 4:10-5:40 am. Final aMT6s acrophases were assessed during the last 24-hours in the laboratory.

There was a significant difference between bright light + exercise vs. exercise. There was no difference between exercise alone vs. bright light alone.

Implication. The circadian phase-shifting effects of bright light and exercise are similar. The shift following bright light + exercise was relatively large and significant.

Return to Table of Contents for this issue.