Static Stretching Acutely Reduces the Ergogenic Effects of Caffeine on Sprint Performance but Not Maximal Ball Velocity in Football Players

This study aimed to investigate the independent and combined effects of caffeine and static stretching (SS) on maximal ball velocity and 30-m sprint performance. Sixteen male amateur football players performed 30-m sprint and an instep kicking ball velocity test under six conditions. The six conditions were control, SS only, placebo only, placebo combined with SS (PLA + SS), caffeine only, and caffeine combined with SS (CAF + SS). A repeated measures ANOVA revealed no significant main effect of condition on maximal ball velocity (F(5, 75) = 1.11, p = 0.36, eta(2)(p) = 0.069). In contrast, a significant main effect of condition was observed for 30-m sprint performance (F(5, 75) = 4.57, p = 0.001, eta(2)(p) = 0.23). Our findings showed that the SS condition resulted in similar sprint performance compared to all other conditions (p >= 0.093) except the caffeine condition (p = 0.009). In contrast, the caffeine condition led to faster sprint performance compared to all conditions (p <= 0.010) except CAF + SS (p = 0.184). Additionally, sprint performances in the SS and CAF + SS conditions were similar (p = 0.093). A large effect size (0.94) was observed between the control and CAF conditions, whereas a moderate effect size (0.54) was found when comparing caffeine and CAF + SS conditions. These findings indicate that caffeine intake enhances sprint performance; however, the CAF + SS combination appears to reduce this effect, making it less effective. Although SS does not directly impair sprint performance, it may have the potential to diminish the ergogenic effects of caffeine.