In order to maintain the firmness of your breasts during physical activities sure to wear comfortable sports bra that will prevent them from relaxing.
For a nice and Practice of firm breasts and the next exercise, you can perform at home. Stand facing the wall and lean on it with both hands, which should be at shoulder height.
Right movements as in the classic push-ups, you will receive your upper body toward the wall and goes up, bending your elbows and giving. Repeat the exercise 12 times and do it three times a week.