The effects of different doses of caffeine on maximal strength and strength-endurance in women habituated to caffeine

Abstract

PurposeThe main goal of this study was to assess the acute effects of 3 and 6 mg of caffeine intake per kg of body mass (b.m.) on maximal strength and strength-endurance in women habituated to caffeine. MethodsTwenty-one healthy resistance-trained female university students (23.0±0.9 years, body mass: 59.0±6.6 kg), with a daily caffeine intake of 5.8±2.6 mg/kg/b.m. participated in a randomized, crossover, double-blind design. Each participant performed three experimental sessions after ingesting either a placebo (PLAC) or 3 mg/kg/b.m. (CAF-3) and 6 mg/kg/b.m. (CAF-6) of caffeine. In each experimental session, the participants underwent a 1RM test and a strength-endurance test at 50%1RM in the bench press exercise. Maximal load was measured in the 1RM test and the time under tension, number of preformed repetitions, power output and bar velocity were registered in the strength-endurance test. ResultsThe one-way ANOVA showed a main effect of caffeine on 1RM bench press performance (F=14.74; p<0.01). In comparison to the PLAC (40.48±9.21 kg), CAF-3 (41.68±8.98 kg; p=0.01) and CAF-6 (42.98±8.79 kg; p<0.01) increased 1RM bench press test results. There was also a main effect of caffeine on time under tension during the strength-endurance test (F=13.09; p<0.01). In comparison to the PLAC (53.52±11.44 s), CAF-6 (61.76±15.39 s; p<0.01) significantly increased the time under tension during the maximal strength-endurance test. ConclusionAn acute dose of 3-to-6 mg/kg/b.m. of caffeine improves maximum muscle strength. However, the effect of these doses had minimal ergogenic effect on strength-endurance performance.