Caffeine (1,3,7-trimethylxanthine) belongs to a group of compounds called methylxanthines, which are primarily known for their stimulatory effects.
Caffeine has been shown to enhance a variety of performance outcomes with wide-ranging intensities and durations, and the scientific consensus is moving toward the conclusion that caffeine is mainly enhancing performance outcomes by influencing the central nervous system. More specifically, caffeine’s effects are mostly attributable to its binding to the A1 and A2A adenosine receptors in the brain. However, there is much debate over whether caffeine has direct effects on muscle tissue itself.
This study by Domaszewski et al gave 9mg/kg of caffeine to professional handball players who regularly consume caffeine, and measured muscle contractile properties via tensiomyography before ingestion and one hour later.
In the caffeine group, the ingestion of caffeine led to decreases in contraction time and maximal displacement during electrically stimulated contractions, which suggests that caffeine was directly impacting the contractile properties of the muscle (rather than purely working through the central nervous system). This makes sense, as a previous study (Mohr et al, 1998) reported that caffeine enhanced electrically evoked muscle function in paralyzed study participants.
Moreover, this study would suggest that this direct effect on muscle is observed in well-trained, caffeine-habituated individuals. Mechanistic findings like these are informative and important, but they don’t always have an immediate impact on practical application. Nonetheless, this is yet another study indicating that the effects of caffeine are still observable in regular caffeine users (in this case, averaging 351mg/day with no period of withdrawal or abstention leading up to the study).
For a comprehensive caffeine guide with practical applications, check out our article: The Lifter’s Guide to Caffeine