What Dose of Caffeine to Use: Acute Effects of 3 Doses of Caffeine on Muscle Endurance and Strength

Purpose: To explore the effects of 3 doses of caffeine on muscle strength and muscle endurance. Methods: Twenty-eight resistance-trained men completed the testing sessions under 5 conditions: no-placebo control, placebo control, and with caffeine doses of 2, 4, and 6 mg.kg(-1). Muscle strength was assessed using the 1-repetition-maximum test: muscle endurance was assessed by having the participants perform a maximal number of repetitions with 60% 1-repetition maximum. Results: In comparison with both control conditions, only a caffeine dose of 2 mg.kg(-1) enhanced lower-body strength (d= 0.13-0.15). In comparison with the no-placebo control condition, caffeine doses of 4 and 6 mg.kg(-1) enhanced upper-body strength (d= 0.07-0.09) with a significant linear trend for the effectiveness of different doses of caffeine (P = .020). Compared with both control conditions, all 3 caffeine doses enhanced lower-body muscle endurance (d= 0.46-0.68). For upper-body muscle endurance, this study did not find significant effects of caffeine. Conclusions: This study revealed a linear trend between the dose of caffeine and its effects on upper-body strength. The study found no clear association between the dose of caffeine and the magnitude of its ergogenic effects on lower-body strength and muscle endurance. From a practical standpoint, the magnitude of caffeine's effects on strength is of questionable relevance. A low dose of caffeine (2 mg.kg(-1))-for an 80-kg individual, the dose of caffeine in 1-2 cups of coffee-may produce substantial improvements in lower-body muscle endurance with the magnitude of the effect being similar to that attained using higher doses of caffeine.