Performance effects beyond feeling alert
Caffeine's best-known action is blocking adenosine receptors, which reduces the sense of drowsiness, but its value as an ergogenic aid goes further. A consistent finding is a lower rating of perceived exertion, meaning a given workload feels easier. Caffeine can also support force and power output and influences the central nervous system in ways that may aid recruitment, which together help explain measurable performance gains across endurance and some strength tasks.
The glycogen-sparing idea, that caffeine shifts fuel use toward fat and preserves muscle glycogen, was an early proposed mechanism but is now considered a smaller or inconsistent contributor compared with the central, perception-based effects.
Dose, tolerance, and individual variation
Ergogenic benefit is usually seen in a moderate dose range, and higher doses raise side effects such as jitters, raised heart rate, and disrupted sleep without proportionally more benefit. Genetics and habitual intake affect response, so the effect is real but variable rather than uniform.
This is general educational information, not medical advice. Caffeine can be unsafe in excess and interacts with several conditions and medications. Consult a qualified professional if unsure.