Researchers recruited 94 resistance-trained men and women for a randomized, double-blind, placebo-controlled trial, which is basically the gold standard of study design. Participants were given either 3 mg/kg of caffeine or a placebo about an hour before performing bench press and squat exercises. 3 mg/kg looks like just over two 8 ounce cups of coffee a day for a 150lb person, which is a pretty modest amount.
