Use a good sports bra!
Research has shown that breasts move about 8 cm when a person does some serious running. This is not good for your breasts. With a good sportsbra you can reduce the movement with 80 percent. So go to the shops and buy yourself a good sports bra! After 6 months you must replace your bra’s for new ones, because the elasticity of the bra’ s is not that good anymore. This can save you backproblems.