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The purpose of this study was to determine the oral dose of caffeine needed to increase muscle force and power output during all-out single multijoint movements.Thirteen resistance-trained men underwent a battery of muscle strength and power tests in a randomized, double-blind, crossover design, under four different conditions: (a) placebo ingestion (PLAC) or with caffeine ingestion at doses of (b) 3 mg·kg−1 body weight (CAFF3mg), (c) 6 mg·kg−1 (CAFF6mg), and (d) 9 mg·kg−1 (CAFF9mg). The muscle strength and power tests consisted in the measurement of bar displacement velocity and muscle power output during free-weight full-squat (SQ) and bench press (BP) exercises against four incremental loads (25%, 50%, 75%, and 90% one-repetition maximum [1RM]). Cycling peak power output was measured using a 4-s inertial load test. Caffeine side effects were evaluated at the end of each trial and 24 h later.Mean propulsive velocity at light loads (25%–50% 1RM) increased significantly above PLAC for all caffeine doses (5.4%–8.5%, P = 0.039–0.003). At the medium load (75% 1RM), CAFF3mg did not improve SQ or BP muscle power or BP velocity. CAFF9mg was needed to enhance BP velocity and SQ power at the heaviest load (90% 1RM) and cycling peak power output (6.8%–11.7%, P = 0.03–0.05). The CAFF9mg trial drastically increased the frequency of the adverse side effects (15%–62%).The ergogenic dose of caffeine required to enhance neuromuscular performance during a single all-out contraction depends on the magnitude of load used. A dose of 3 mg·kg−1 is enough to improve high-velocity muscle actions against low loads, whereas a higher caffeine dose (9 mg·kg−1) is necessary against high loads, despite the appearance of adverse side effects.