The purpose of this study was to investigate the effect of timed exercise on human circadian rhythms. Subjects were randomized to 5 days of morning or evening treadmill exercise. A measure of internal circadian timing, or phase, was measured at baseline and following the exercise intervention. Change in circadian phase was compared between the morning and evening group.
This study investigated the effect of morning versus evening exercise on internal circadian timing, or phase. Young, sedentary subjects were recruited for this study. Baseline measures included anthropometric, body composition, cardiorespiratory fitness, chronotype, and circadian phase. Subjects were randomized to 5 consecutive days of morning or evening exercise. Thirty minutes of exercise was performed at the designated time and intensity was maintained at a heart rate corresponding with 70% peak VO2. The measure of circadian phase was salivary dim light melatonin onset, indicated by the time when saliva melatonin concentration exceeded 4pg/ml. Post-exercise circadian phase was measured the evening following the last day of exercise. Changes in circadian phase were compared between morning and evening groups.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
67
moderate intensity exercise (70% VO2 max) each morning for 5 days
moderate intensity exercise (70% VO2 max) each evening for 5 days
University of Kentucky
Lexington, Kentucky, United States
Change in onset (time) of melatonin secretion
Difference in onset (time at which salivary melatonin exceeds threshhold; 4pg/mL) from baseline to completion of exercise intervention.
Time frame: baseline and following completion of exercise intervention (approximately 5 days)
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