You’ll find caffeine everywhere on the endurance circuit, popping up in a slew of products—powders, gels, drink, chews, gums, and even sprays. Evidence of its potential as a performance enhancer has been around for years, but scientists and athletes alike are still unpacking the nuances—and the legality—of its application.
Caffeine stimulates the central nervous system, says Todd Astorino, a professor of kinesiology at California State University, San Marcos. It blocks the adenosine receptors (responsible for fatigue), which, in turn, makes you feel less tired. “There is also some evidence that caffeine reduces feelings of muscle pain and perceived exertion, especially during endurance-based exercise,” Astorino says. Other reports tout perks such as increased activation of muscle fibers, leading you to feel faster and stronger, and enhanced mood, which makes long-term repetitive efforts less daunting.