Acute Effects of Caffeine Supplementation on Movement Velocity in Resistance Exercise: A Systematic Review and Meta-analysis

Background Several studies investigated the effects of caffeine supplementation on movement velocity in resistance exercise. However, these studies presented inconsistent findings. Objective This paper aimed to: (a) review the studies that explored the effects of caffeine supplementation on movement velocity in resistance exercise; and (b) pool their results using a meta-analysis. Methods A search for studies was performed through seven databases. Random-effects meta-analyses of standardized mean differences (SMD) were performed to analyze the data. Sub-group meta-analyses explored the effects of caffeine on different velocity variables (i.e., mean and peak velocity), different loads (i.e., low, moderate, and high loads), and upper- and lower-body exercises. Results Twelve studies met the inclusion criteria. In the main meta-analysis, in which we pooled all available studies, the SMD favored the caffeine condition (SMD = 0.62; 95% confidence interval [CI]: 0.39-0.84; p < 0.001). Sub-group analyses indicated that caffeine significantly enhances mean (SMD = 0.80; 95% CI: 0.48-1.12; p < 0.001) and peak velocity (SMD = 0.41; 95% CI: 0.08-0.75; p = 0.014), movement velocity with low loads (SMD = 0.78; 95% CI: 0.41-1.14; p < 0.001), moderate loads (SMD = 0.58; 95% CI: 0.25-0.91; p = 0.001), and high loads (SMD = 0.70; 95% CI: 0.33-1.07; p < 0.001), as well as in lower-body (SMD = 0.82; 95% CI: 0.42-1.23; p < 0.001) and upper-body exercises (SMD = 0.59; 95% CI: 0.37-0.82; p < 0.001). Conclusion Acute caffeine supplementation is highly ergogenic for movement velocity in resistance exercise. Sub-group analyses indicated that caffeine ingestion is ergogenic: (a) for both mean and peak velocity; (b) for movement velocity when exercising with low, moderate and high loads, and (c) for movement velocity in both lower- and upper-body exercises. Previous meta-analyses that explored the effects of caffeine on various aspects of resistance exercise performance (i.e., muscular strength and endurance) reported trivial to moderate ergogenic effects (effect size range: 0.16-0.38). In the present meta-analysis, the pooled effect size ranged from 0.41 to 0.82. From a resistance exercise performance standpoint, this suggests that caffeine has the most pronounced performance-enhancing effects on movement velocity.