Burton, N. B., Hardy, M. A., Glaser, r. H., Honeycutt, A. H., Hubier, M. B., Ready, C. M., & Warren, G. L. (2009). Effects of caffeinated and uncaffeinated energy drinks on muscular strength and endurance. ACSM 56th Annual Meeting, Seattle, Washington. Presentation number 1901.

This study compared a caffeinated energy drink’s effect on muscle activation and strength with that of placebo and an uncaffeinated energy drink. College students (N = 15) performed three trials, ingesting either a caffeinated energy drink ("Full Throttle", The Coca-Cola Company), an uncaffeinated version of the energy drink, or a placebo drink. The interpolated twitch procedure was used to assess maximum voluntary isometric contraction strength, electrically-evoked strength, and muscle activation during maximum voluntary isometric contraction of the knee extensors both before and after drink ingestion, and after a fatiguing bout of 50 concentric contractions.

The mean change in maximum voluntary isometric contraction strength from before to after drink ingestion was greater for the caffeinated and uncaffeinated energy drinks than in the placebo condition. There was no significant difference between the two energy drinks. There was no effect of drink type on the changes in electrically-evoked strength or muscle activation from before to after drink ingestion. In addition, there was no effect of drink type on the changes in any variable from before to after the fatiguing bout of contractions. The similar increase in maximum voluntary isometric contraction strength from before to after drink ingestion of the two energy drinks is not easily explained. The caffeinated energy drink significantly increased the plasma glucose level over that for placebo whereas the uncaffeinated drink did not. Furthermore, the serum caffeine level was 14-fold greater with the caffeinated energy drink compared to the uncaffeinated drink.

Implication. Both caffeinated and uncaffeinated energy drinks increase maximum voluntary isometric contraction strength in an unfatigued state but the mechanism for the ergogenic effect is unclear. The observed effects may be an artifact of the untrained Ss involved in the study.

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