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 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 significant increase in 1RM for CAF-6 when compared to CAF-3 (p < 0.01). There was 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 strength. However, these doses of caffeine had minimal ergogenic effect on strength-endurance performance in women habituated to caffeine.
Highlights
The acute intake of caffeine (CAF) has been found effective in enhancing exercise performance in a wide range of resistance-based exercises based on strengthendurance [1,2,3], and strength-power exercise modalities [4, 5]
The post-hoc tests revealed a significant increase in 1RM after the intake of CAF-3 (41.68 ± 8.98 kg; p = 0.01) and CAF-6 (42.98 ± 8.79 kg; p < 0.01) compared to PLAC (40.48 ± 9.21 kg), as well as a difference between CAF-6 compared to CAF-3 (p < 0.01; Table 3; Fig. 1)
The post-hoc tests revealed a significant increase in time under tension after the intake of CAF-6 compared to PLAC (61.76 ± 15.39 vs. 53.52 ± 11.44 s, respectively p < 0.01), and lack of significant changes in time under tension between CAF-3 and PLAC (57.05 ± 10.9 s p = 0.20)
Summary
The acute intake of caffeine (CAF) has been found effective in enhancing exercise performance in a wide range of resistance-based exercises based on strengthendurance [1,2,3], and strength-power exercise modalities [4, 5]. The effect of CAF on multiple body tissues makes it difficult to accurately determine the key mechanism of action during exercise. Several mechanisms, such as reduced muscle pain and perceived exertion [17], enhanced fat oxidation [18], increased muscle oxygen saturation [19] and local changes within the exercising muscle [20], have been proposed to explain caffeine’s ergogenic effects, most of them explain the effect of CAF on submaximal exercise intensity. Evidence in animal [13] and human models [23] supports the capacity of CAF to act as an adenosine A1 and A2A receptor antagonist, inhibiting the brake that endogenous adenosine imposes on the ascending dopamine and arousal systems [14]
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