Effects of time-of-day on neuromuscular function in untrained men: Specific responses of high morning performers and high evening performers

It has been clearly established that maximal force varies during the day in human muscles but the exact mechanisms behind the diurnal rhythms are still not fully clarified. Therefore, the aim of this study was to examine the diurnal rhythms in maximal isometric force production in a large group of participants and also by separating the high morning performance types (n = 8) and the high evening performance types (n = 19) from the neutral types (n = 45) based on their actual maximal isometric force levels. Measurements were performed in the morning (7:26 h ± 63 min) and in the evening (17:57 h ± 74 min) for maximal bilateral isometric leg press force (MVCLP) together with myoelectric activity (EMGLP), maximal unilateral isometric knee extension force (MVCKE) and maximal voluntary activation level (VA%) during maximal unilateral isometric knee extension force (MVCVA) together with myoelectric activity (EMGVA). In addition, venous blood samples were drawn four times a day and serum testosterone and cortisol...