Time of day has no effect on maximal aerobic and peak power

N Bessot^1,3, S Moussay^1,2, B Dufour^1,2, D Davenne^1,2, B Sesboüé^1,3, A Gauthier^1,2
1Inserm, ERI27, Caen, France; ²University Caen, Caen, France; ³CHRU Caen, Explorations Fonctionnelles, Caen, France

Background: The aim of this study was to explore the effect of time of day on peak power reached during an exercise test and maximal aerobic power achieved when the subject reached maximal oxygen uptake.
Methods: Fifteen male competitive endurance cyclists performed a standardized maximal incremental exercise test at 06:00 hours and 18:00 hours. The test began with a 5-minute warmup period at a workload of 150 W. The work rate was then increased by incremental steps of 30 W per minute until the respiratory exchange ratio reached 1.00. Thereafter, workload was increased in steps of 15 W per minute until exhaustion was reached.
Results: No significant diurnal variation was detected in physiological parameters (maximal oxygen uptake and maximal heart rate) or biomechanical parameters (maximal aerobic power, peak power).
Conclusion: Circadian variations classically reported in competitive aerobic performances could be due to fluctuations in maximal aerobic endurance and/or improvement in gestural efficiency (pattern of muscle activity, effective force production, and kinematics).

Keywords: chronobiology, maximal aerobic power, peak power, maximal oxygen uptake, maximal incremental test