Caffeine is a stimulant that can enhance physical performance by improving focus, decreasing perceived effort, and increasing endurance. It works by blocking adenosine, a neurotransmitter that promotes sleep and relaxation, which can lead to increased alertness. This improved mental state often translates to superior performance in activities requiring endurance, strength, or speed. Additionally, some studies suggest that caffeine can enhance glycogen resynthesis and increase fat oxidation, making it a popular ergogenic aid among athletes.