Blonc, S, Perrot, S, Racinais, S, Aussepe, S, and Hue, O. Effects of 5 weeks of training at the same time of day on the diurnal variations of maximal muscle power performance. J Strength Cond Res 24(1): 23-29, 2010-The purpose of this study was to investigate whether maximal muscle power production in humans is influenced by the habitual time of training to provide recommendations for adapting training hours in the month preceding a competition. Sixteen participants performed maximal brief squat and countermovement jumps and short-term cycle sprints tests before and after 5 weeks of training. Subjects were randomly assigned to either a Morning-Trained Group (MTG, 7:00-9:00 hr) or an Evening-Trained Group (ETG, 17:00-19:00 hr). They trained and performed the evaluation tests in both the morning and evening in their naturally warm and moderately humid environment. The results indicated a significant increase in performance (approximately 5-6% for both tests) after training for both groups but failed to show any time-of-day effect on either performance or training benefit. These findings could be linked to the stabilization of performances throughout the day because of the passive warm-up effect of the environment. In summary, our data showed that anaerobic muscle power production could be performed at any time of day with the same benefit.