Most people know that music can make a workout easier, but which music makes it easiest? NPR reports that Costas Karageorghis, deputy head of research at the School of Sport and Education at Brunel University in West London, has spent years researching the links between exercise, heart rates and music tempo. What has he learned? With background music, he says, we can reduce our perception of effort expended by about 10 percent, especially if the music's tempo is between 125 and 140 beats per minute. Wait, there's more: songs give us an additional bump, he says, when there are emotional ties. Karageorghis cites the lyrics to Kanye West's hip-hop hit "Stronger," which "lifts the spirit, lifts the mood and gets people to push just that little bit harder," he says, even though the tempo isn't particularly fast.