Acute doses of 3 and 6 mg/kg caffeine produce outcome- and phase-specific improvements in male 100-m sprinters: A randomized, double-blind, placebo-controlled crossover trial

Evidence is limited on whether commonly used caffeine doses provide uniform benefits across sprint phases and performance outcomes in trained sprinters. We compared the acute effects of 3 and 6 mg/kg caffeine in a randomized, double-blind, placebo-controlled, three-condition crossover trial. Twenty-one male 100-m sprinters completed placebo, 3 mg/kg caffeine, and 6 mg/kg caffeine trials separated by at least 7 days. Sixty minutes after ingestion, participants completed two maximal 60-m sprints, followed by countermovement jump, squat jump, and 10-s Wingate tests. Sprint times, derived split times, start reaction time, starting-block rate of force development, stride variables, and perceived exertion were also assessed. Linear mixed-effects models adjusting for treatment period and randomized sequence showed clear treatment effects for cumulative 10-, 30-, and 60-m times (all p < 0.001). Relative to placebo, 3 mg/kg shortened these times by 0.056, 0.083, and 0.123 s, whereas 6 mg/kg shortened them by 0.075, 0.115, and 0.175 s. Compared with 3 mg/kg, 6 mg/kg further reduced 30- and 60-m times by 0.032 and 0.052 s, respectively, whereas the additional 0.019-s reduction at 10 m was not statistically significant in the primary mixed-effects model. Both doses improved reaction time, perceived exertion, jump height, Wingate peak and mean power, and starting-block rate of force development relative to placebo. Additional benefits of 6 mg/kg were evident for jump height and rate of force development, but not for reaction time, perceived exertion, or Wingate mean power; Wingate peak power did not improve further with the higher dose. Stride length and frequency were unchanged. These findings indicate outcome-specific dose responses, with 3 mg/kg improving multiple performance outcomes and 6 mg/kg providing additional benefits most consistently for vertical jump height, starting-block rate of force development, and cumulative performance over the first 60 m. Trial registration Chinese Clinical Trial Registry, ChiCTR2600128594 .