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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.
Grgic, Bishop, and Pedisic are with the Inst for Health and Sport, Victoria University, Melbourne, Australia. Sabol is with Fitness Academy, Zagreb, Croatia. Sabol, Venier, I. Mikulic, and P. Mikulic are with the Faculty of Kinesiology, University of Zagreb, Zagreb, Croatia. Bratkovic is with Nutri Klinika, Zagreb, Croatia. Schoenfeld is with the Dept. of Health Sciences, Lehman College, Bronx, NY. Pickering is with the School of Sport and Wellbeing, Inst of Coaching and Performance, University of Central Lancashire, Preston, United Kingdom. Bishop is also with the School of Medical and Health Sciences, Edith Cowan University, Joondalup, WA, Australia.