Can Caffeine be Used to Enhance Muscular Strength, Power, and Endurance Performance

Abstract

The performance enhancing potential of acute caffeine consumption has been established, with meta-analyses confirming benefits for aerobic endurance, anaerobic power, muscular strength, and endurance, as well as facets of physical performance important for sport performance. Despite the wealth of evidence, there is nearly exponential growth in the publication of studies examining caffeine’s ergogenic effects which is needed to develop and understand how to optimise caffeine performance enhancing benefits. One particular area of the literature where results are considered to be more ambiguous is the understanding of caffeine’s effect on muscular function. The thesis makes a novel contribution to the evidence base by examining acute and chronic supplementation of caffeine on measures of muscular strength, power, and endurance, and more specifically provides the first robust assessment of chronic caffeine consumption for augmenting the effects of resistance training while considering the potential paradoxical effects of habituation of caffeine on physical performance. Furthermore, given the growing interest in alternative modes of caffeine consumption and the potential for performance enhancing effects via different mechanisms. This thesis provides the first direct comparison of different caffeine modalities (capsule, chewing gum, and mouth rinsing) on measures of muscular function. Moreover, it is common practice in the sport science research to determine test-retest reliability of desired outcomes measures; however, no study is yet to evaluate the repeatability of caffeine effects on muscular function which is presented for the first time in this thesis. The aim of the thesis were addressed by drawing upon several quantitative assessments of muscular strength, power, and endurance evaluated using isometric dynamometry, isometric mid-thigh pull performance, countermovement jumps, drop jumps, one repetition maximum and repetition until failure during resistance exercise. The data presented in this thesis demonstrate that the ingestion of 3 mg.kg-1 of caffeine causes small but significant improvements in muscular function; however, these effects are muscle and contractile mode specific. Chronic caffeine consumption of 3 mg.kg-1 twice weekly over a 7-week resistance training intervention did not result in superior training adaptations when compared to a placebo group. Consumption of caffeine 14 times over a 7-week training intervention did not impair the effectiveness of acute caffeine supplementation on measures of muscular function. Caffeine administered via a capsule, chewing gum, and mouth rinse at a matched dose of 3 mg.kg-1 collectively elicited small but significant improvements in specific measures of muscular function, but no superiority was found when modalities were compared. Acute supplementation of 3 mg.kg-1 of caffeine on measures of muscular strength, power, and endurance present poor repeatability across multiple trials suggesting potential day-today variation. The findings have important practical implications for athletes, sports nutritionists, and the scientific community. Importantly, athletes may consider using caffeine to evoke small but significant improvements in muscular function and may consider consumption via capsule, gum, or mouth rinse depending on the environment and individual constraints that may limit caffeine consumption. Although chronic moderate dose caffeine consumption appears not to result in habituation, the evidence presented in this thesis suggests little benefit of caffeine pre-exercise for augmenting the effects of resistance training. In light of the muscle and contractile mode specific nature of caffeine effects and the limited repeatability of demonstrated benefits, caffeine may not effectively enhance performance for all athletes and on all occasions. Finally, given the lack of repeatability of caffeine’s effect, which may be driven by daily variation in mood, future work examining the ergogenic effect of caffeine on physical performance should consider evaluating effects over repeated trials so to avoid misleading conclusions.

Date of Award	May 2024
Original language	English
Awarding Institution	Coventry University
Supervisor	Jason Tallis (Supervisor), Neil Clarke (Supervisor), Michael Duncan (Supervisor) & Rhys Morris (Supervisor)