We all know caffeine provides an energy boost, but science is still investigating how quickly it can kick in and how much difference that might make in the gym. For a study published in the December 2010 issue of Medicine & Science in Sports & Exercise, researchers had 15 active men perform two bouts of 40 reps of knee-extension and knee-flexion exercises during three separate trials. Before the trials, some men received 5 milligrams of caffeine per kilogram of bodyweight, some received 2 milligrams and some received a placebo. Result? Those with the higher caffeine boost experienced 5 percent to 8 percent better peak knee-flexion torque, knee-extension/flexion total work and knee-extension/flexion power during the first bout of reps and no significant effect during the second bout. In other words, going big with caffeine can make for a potent workout surge. Yes, the effect is limited, but it may just help you bust through a plateau.