Effect of time-of-day-specific strength training on maximum strength and EMG activity of the leg extensors in men

In this study, we examined the effects of time-of-day-specific strength training on maximum strength and electromyography (EMG) of the knee extensors in men. After a 10-week preparatory training period ( training times 17: 00-19: 00 h), 27 participants were randomized into a morning ( 07:00-09: 00 h, n = 14) and an evening group ( 17: 00-19.00 h, n 13). Both groups then underwent 10 weeks of time-of-day-specific training. A matched control group ( n 7) completed all testing but did not train. Unilateral isometric knee extension peak torque (MVC) and one-repetition maximum half-squat were assessed before and after the preparatory training and after the time-of-day-specific training at times that were not training-specific ( between 09: 00 and 16: 00 h). During training-specific hours, peak torque and EMG during MVC and submaximum isometric contraction at 40% MVC were assessed before and after the time-of-day-specific training. The main finding was that a significant diurnal difference (P < 50.01) in peak torque between the 07: 00 and 17: 00 h tests decreased after time-of-day-specific training in the morning group but not in the evening or control groups. However, the extent of this time-of-day-specific adaptation varied between individuals. Electromyography during MVC did not show any time-of-day-specific adaptation, suggesting that peripheral rather than neural adaptations are the main source of temporal specificity in strength training.