Effect of Caffeine Ingestion on Muscular Strength and Endurance: a Meta-Analysis.
Warren GL, Park ND, Maresca RD, McKibans KI, Millard-Stafford ML.
PURPOSE:: Our objective was to perform a systematic review and meta-analysis of the research literature assessing the effect of caffeine ingestion on maximal voluntary contraction (MVC) strength and muscular endurance. METHODS:: Thirty-four relevant studies between 1939 and 2008 were included in the meta-analyses of caffeine's effects on MVC strength (n = 27 studies) and muscular endurance (n = 23 studies). Effect sizes were calculated as the standardized mean difference and meta-analyses were completed using a random-effects model. RESULTS:: Overall, caffeine ingestion was found to result in a small beneficial effect on MVC strength [overall effect size (ES) = 0.19, P = 0.0003]. However, caffeine appears to improve MVC strength primarily in the knee extensors (i.e., by ~7%; ES = 0.37) and not in other muscle groups such as the forearm or knee flexors. In an attempt to offer a physiological mechanism behind caffeine's ability to improve MVC strength, a meta-analysis was run on effect sizes from nine studies that measured percent muscle activation during MVC in trials comparing caffeine versus placebo; the overall ES (0.67) was highly significant (P = 0.00008) and of moderate to large size, thus implicating an effect of caffeine on the central nervous system. Caffeine ingestion was also found to exert a small beneficial effect on muscular endurance (overall ES = 0.28, P = 0.00005). However, it appears caffeine improves muscular endurance only when it is assessed using open- (i.e., by ~18%; ES = 0.37) and not fixed-endpoint tests. CONCLUSIONS:: Overall, caffeine ingestion improves MVC strength and muscular endurance. The effect on strength appears exclusively in the knee extensors and the effect on muscular endurance appears only detectable with openendpoint tests.
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L' It alia vive in biciclletta.
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