C. Larson,M. Pillo, C. Tangeman, R. Ueda, W.M. Silvers

Whitworth University, Spokane, WA

Researchers have observed the positive effect of small doses (i.e., 5 mg/kg) of caffeine on endurance performance, but research with short-term, high-intensity activities, such as the vertical jump has produced equivocal results. PURPOSE: The purpose of this study was to test the effects of caffeine supplementation on vertical jump height and force output in college-aged individuals. METHODS: In this randomized single-blind crossover study, 27 undergraduate students (nm= 10, nf= 17) attended two sessions and received a 12 oz drink that contained either a caffeine supplement or a placebo. The amount of caffeine given to each participant was based on body weight (i.e., 5 mg/ kg of body mass). At each session, participants consumed the assigned drink, waited 55 min, and performed a 5 min warm up that consisted of cycling at a mild intensity. Participants then performed three maximal-effort countermovement vertical jumps, each 30 s apart. A Just Jump mat (Power Systems, Knoxville, TN) was used to measure jump height. Peak force was measured and recorded with the AMTI Optima HPS Force Plate (Advanced Mechanical Technology, Inc., Watertown, MA). Each participant’s highest measurements for jump height (cm) and peak force output (N) from each session were used for data analysis. Wilcoxon Signed-Rank tests were utilized to analyze the data (significance level p≤ 0.05).RESULTS: There were no significant differences observed between conditions for peak force output (p = 0.66) and vertical jump height (p = 0.68). The placebo elicited an average peak force production of 1865.6 ± 529.8 N and an average vertical jump height of 53.2 ± 15.5 cm. The caffeine elicited an average peak force production of 1868 ± 477.9 N and an average vertical jump height of 53.4 ± 16.3 cm. CONCLUSIONS: Under these conditions, caffeine elicited no significant differences in jump performance. Due to the small sample size (n = 27) and high beta values (β = 0.973 - 0.974), there was a high probability that a type II error was committed. In addition, jump performances for individual participants were inconsistent between trials. Future research should include larger sample sizes, an isolated testing environment to reduce competition, and detailed jump technique demonstrations to reduce jump inconsistency.

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