If you want to go from scrawny to brawny in 30 days, there is no shortage of miracle shape-up programs. But as impressive as beefy pecs and triceps may look, they won't help you cite the evidence for Einstein's special theory of relativity, rattle off pi to the 20th decimal place, or liberate yourself from the mass delusion that a penny dropped from the Empire State Building will gather enough speed to kill a hapless pedestrian. We at PopSci believe the body part most worth stretching and toning—not to mention showing off—is the brain.