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.

Full Title of Study: “Investigating the Effects of Timed Exercise on Human Circadian Rhythms”

Study Type

  • Study Type: Interventional
  • Study Design
    • Allocation: Randomized
    • Intervention Model: Parallel Assignment
    • Primary Purpose: Basic Science
    • Masking: None (Open Label)
  • Study Primary Completion Date: March 9, 2019

Detailed Description

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.


  • Other: Morning Exercise
    • moderate intensity exercise (70% VO2 max) each morning for 5 days
  • Other: Evening Exercise
    • moderate intensity exercise (70% VO2 max) each evening for 5 days

Arms, Groups and Cohorts

  • Experimental: Morning Exercise Group
    • Participants perform moderate exercise in the morning.
  • Experimental: Evening Exercise Group
    • Participants perform moderate exercise in the evening.

Clinical Trial Outcome Measures

Primary Measures

  • Change in onset (time) of melatonin secretion
    • Time Frame: baseline and following completion of exercise intervention (approximately 5 days)
    • Difference in onset (time at which salivary melatonin exceeds threshhold; 4pg/mL) from baseline to completion of exercise intervention.

Participating in This Clinical Trial

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

Gender Eligibility: All

Minimum Age: 18 Years

Maximum Age: 45 Years

Are Healthy Volunteers Accepted: Accepts Healthy Volunteers

Investigator Details

  • Lead Sponsor
    • Julie Pendergast
  • Provider of Information About this Clinical Study
    • Sponsor-Investigator: Julie Pendergast, Assistant Professor – University of Kentucky
  • Overall Official(s)
    • Julie Pendergast, Principal Investigator, University of Kentucky

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