Many bodybuilders take caffeine before workouts to increase energy levels and strength. A study led by Todd Astorino from Cal State University, San Marcos, found that high doses of caffeine (approximately 400 mg) increased strength during maximal knee extension-flexion exercise (40 reps knee extension-flexion at 180° per second on an isokinetic dynamometer). A lower dose of caffeine (approximately 160 mg) had no effect on strength-endurance.
Even the most potent energy drinks contain less than 200 mg of caffeine. High doses of caffeine can increase high-intensity strength-endurance by about 6 to 8 percent. Currently, caffeine is not a banned substance for athletes participating in Olympic or professional sports, but the NCAA still limits its use. (Medicine Science Sports Exercise, 42: 2205-2210)