Effect of Time-of-Day on EPOC Magnitude and Duration.

Chia-Ling Lee, Richard P. Mikat, Brian E. Udermann, Karen M. Skemp-Arlt Faculty Advisor: Dr. Richard P. Mikat, Exercise and Sport Science

There is considerable interest in the effect of time-of-day on the caloric cost of exercise. An important component of the caloric cost of exercise is recovery. Because little is known about recovery energy costs at different times of day, the purpose of this study was to examine the effect of time-of-day on Excess Post-Exercise Oxygen Consumption (EPOC) magnitude and duration following a 30-minute bout of moderate-intensity cycling. Eighteen moderate to high aerobically trained women (mean age=21±3 years) volunteered as participants for this study. Each subject performed three-30 minute bouts of exercise on a cycle ergometer at 65% of their age-predicted maximum heart rate. These bouts were separated by at least two days and were randomly ordered for early morning (05:00-07:00), mid-day (11:00-13:00), and early evening (17:00-19:00). Following each exercise bout, subjects rested while their post-exercise oxygen consumption rates were measured by indirect caloricity for 30 minutes. Time and magnitude of EPOC were calculated from this data and were analyzed with repeated measures ANOVA. There were no significant differences (p=0.477) in mean durations of EPOC for morning (15.99±4.10 minutes), mid-day (14.38±4.06 minutes) and evening (16.47±4.70 minutes), or in EPOC magnitude (p=. 877) for morning (17.48±7.50 ml O2/kg), mid-day (18.84±7.77 ml O2/kg) and evening (20.00±5.12 ml O2/kg. The results found no difference in EPOC magnitude and duration across time of a day among trained women. The results suggest that persons interested in finding the optimal conditions in which to exercise beneficially need not focus on time-of-day.

Conclusion:  Time of day doesn't matter when it comes to EPOC (excess postexercise consumption).  The calories burned post workout are used mostly for muscle recovery, which is known as EPOC.  The differences between the times of day were insignificant.

Marc C. David - NGA CPT
Author of NoBull Bodybuilding
www.nobullbodybuilding.com