A good bra helps provide back support and keeps you from suffering chest/breast pain during exercise, since rigorous movements pull on the connective tissues of the breasts. Choose a sports bra that still provides plenty of support for exercise. Wired bras tend to eventually poke through after many laundry cycles, and even when they don't, can poke into the sides of your breasts if they're not the exact right shape. Synthetic fabrics are more breathable than cotton and help prevent irritation from lack of moisture-wicking. Champion offers various fabrics like Lycra and nylon for bras that have been highly rated for high-impact exercise in a study commissioned by the American Council on Exercise. Nike has a DriFit top with a liner bra that is comfortable for medium-impact exercise.