Acute effects of 3 and 6 mg·Kg −1 caffeine on strength–power performance and isokinetic peak torque in competitive male boxers: a randomized, double-blind, placebo-controlled crossover trial

Background Evidence on the dose, timing, and task specificity of caffeine ingestion in combat-sport athletes remains limited. This study examined the acute effects of 3 and 6 mg·kg−1 caffeine on strength–power performance and isokinetic peak torque in male boxers.Methods Fifteen male boxers who met the Chinese national second-class athlete standard or higher completed a randomized, double-blind, placebo-controlled crossover trial. Each participant completed placebo (PLA), 3 mg·kg−1 caffeine (CAF3), and 6 mg·kg−1 caffeine (CAF6) conditions in randomized order, separated by a 1-week washout. Countermovement jump (CMJ), ballistic push-up (BPU), and dominant-side shoulder and knee isokinetic peak torque (PT) were assessed at baseline and during testing blocks beginning at 30 and 60 min post-ingestion. Data were analyzed using two-way repeated-measures ANOVA, with Holm adjustment applied across the 10 planned condition × time interaction tests. Reliability analyzes were supportive, and threshold-based individual classifications were exploratory.Results Significant condition × time interactions were observed for CMJ, BPU, and isokinetic PT outcomes. During the scheduled 60-min assessment, CAF3 and CAF6 produced higher CMJ jump height, peak power, and relative peak power than PLA, with no significant difference between caffeine doses. For BPU, CAF6 produced higher concentric impulse, concentric mean power, and concentric peak power than PLA during the scheduled 60-min assessment, whereas CAF3 did not differ from PLA. Shoulder flexion and extension PT increased under caffeine conditions at selected time points, without a consistent dose advantage. Knee extension PT showed the clearest dose-specific response, with CAF6 exceeding both PLA and CAF3 during the scheduled 60-min assessment.Conclusions Acute ingestion of 3 and 6 mg·kg−1 caffeine was associated with improvements in selected laboratory-based strength–power and isokinetic PT outcomes in male boxers, particularly during the scheduled 60-min assessment. The pattern of responses varied across doses and testing tasks, and 6 mg·kg−1 was not consistently superior to 3 mg·kg−1. These findings should be interpreted as evidence for selected neuromuscular outcomes rather than as direct evidence of improved punching or competitive boxing performance.