Filed under: FitnessPhoto: CorbisThere are two exercise camps. The first is made up of people who take a Zen-like approach to working out, preferring to be left alone with their thoughts while pumping iron or hauling it on the treadmill. The second is for those who rely on steady beats of their favorite song to pull them through that last rep or mile. If you're a thoughtful exerciser, more power to you, but new research shows that jamming out while you're working out can actually increase your e