Sex-Specific Effects of Diurnal Variation on Neuromuscular Performance in Volleyball Players

Neuromuscular performance is influenced by diurnal variation, but it remains unclear whether sex moderates these patterns in team sport athletes. This study examined whether sex moderates the effect of time of day on neuromuscular performance in volleyball players.

One hundred and two volleyball players (46 males and 56 females) completed a randomized battery of tests in the morning (08:00-10:00) and evening (18:00-20:00) on separate days. The battery included vertical jumps (squat, countermovement, and spike jumps), spike performance (standing and jumping spike), agility (modified T test), isometric handgrip strength, and dynamic balance (modified star excursion balance test).

A significant sex-by-time interaction was observed in squat jump (P  =  .002, ηp2=.09), with males showing higher evening values, whereas females showed no significant change. A sex-by-time interaction was also found in jumping spike (P = .045, ηp2=.04), agility (P = .027, ηp2=.05), and dynamic balance (ie, posterolateral) on the dominant leg (P = .005, d = 0.26), reflecting different response patterns between sexes. No significant changes were observed in other dynamic balance directions (P > .05). A significant time-of-day effect was observed, indicating higher evening performance in all jump tests (P = .005, ηp2=.08-.19), ball velocity in spike velocity (P = .002, ηp2=.09), and isometric handgrip strength (P = .001, ηp2≈.10).

Sex-specific differences were limited to a few tasks and were generally small in magnitude, whereas a consistent enhancement in neuromuscular performance in the evening compared with the morning emerged as the primary finding, regardless of sex.