Sex differences in the acute effect of caffeine on repeated sprint performance: A randomized controlled trial

This study aimed to examine sex differences in acute caffeine intake on repeated sprint performance. Fifty-two resistance-trained individuals (age: 24.6 ± 4.5 years and sex (female/male): 26/26) participated in a randomized, triple-blind, cross-over, and placebo-controlled study. Participants ingested 3 mg/kg caffeine or placebo and, after 60 min, performed 4 Wingate tests (Wt), consisting of a 30 s all-out lower-body sprint against an individualized resisted load, with 90 s rest periods between sprints. Mean (W_mean) and peak (W_peak) power showed an interaction between sprint and supplement (P = 0.038, η_p ² = 0.095 and P < 0.001, η_p ² = 0.157, respectively), but only W_peak reported a supplement and sex interaction (P = 0.049 and η_p ² = 0.166). Caffeine increased W_mean in Wt3 (3.5%, P = 0.004, and g = 1.059) and Wt4 (3.9%, P = 0.012, and g = 1.091) compared to placebo. Whereas, for W_peak, caffeine increased W_peak in the Wt1 (2.9%, P = 0.050 and g = 1.01) and Wt2 (3.2%, P = 0.050, and g = 1.01) in males and in Wt3 (5.2%, P = 0.008, and g = 1.79) and Wt4 (8.1%, P = 0.004, and g = 2.27) in female participants compared to placebo. No statistically significant sex differences were found in time to reach W_peak, fatigue index. Acute caffeine intake stimulated a similar ergogenic effect on repeated sprint performance in men and women, except in peak power output, where caffeine increased performance during the first sprints in males and the last sprints in female participants.