Timed Exercise Study
Timed Exercise Study
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.
Inclusion Criteria:

 -  BMI 18.5-40.0

 -  sedentary; <=2 hrs structured exercise weekly

 -  medication free (other than birth control)

 Exclusion Criteria:

 -  diagnosed conditions that would contraindicate safe participation in physical activity

 -  diagnosed psychiatric conditions

 -  night or rotating shift work 1-year prior to study

 -  travel across time zones within previous 4 weeks

 -  having children <2 years of age

 -  smoking