Many bodybuilders take caffeine pills or energy beverages containing caffeine (e.g., coffee or Red Bull) to increase training intensity. Caffeine is a central nervous stimulant used to prevent fatigue and promote mental alertness. Most studies show that caffeine does not increase muscle strength or power, but reduces the perception of fatigue.
New Zealand researchers found that caffeine increased testosterone levels during training, with higher doses of caffeine producing higher blood levels of testosterone. Increased testosterone levels make it easier to gain muscle mass and strength with training. The study also showed that caffeine increased cortisol— a catabolic hormone linked to protein breakdown, which might nullify caffeine’s beneficial effects on testosterone. Caffeine provides an energy boost to train harder and might also promote training gains by increasing testosterone levels.