Need about 8 No-Doz or cups of coffee for caffeine to act as a vasodialator, opening your blood vessels to allow you to stay in an aerobic state. This means it is an illegal drug in many sports, especially cycling. Btw, tennis requires short bursts of energy, an anaerobic activity. May not improve performance.
WOMENS TENNIS WON'T DRAW FLIES BUT SOMETIMES IT SHOULD