>> miley cyrus. >> reporter: one study shows it can boost your athletic performance by up to 15%. a survey in one magazine found acdc's "back in black" is a top workout song of all time. but science finds 20 songs that have between 120 and 140 beats per minute that most ignite the inner rocky in you. ♪ that means the best workout songs are like blurred lines at 120 beats per minute. "gangnam style," 132 beats her minute. ♪ >> reporter: but rocky's "eye of the tiger" -- ♪ >> reporter: a wimpy 109. but if rocking beats aren't enough to get you working out, how about a few bucks? apps like gym pack discovered a new way to get knew the gym. you sign one your credit card. your money goes into a pot. the app tracks when you sign in at the gym and stay for at least 30 minutes. if you go, you pay as little as