Are breasts made up of muscles and fat?
No, Breasts are actually made up of glandular tissues and fat and it is held in position by a delicate Cooper's Ligament

If I exercise, will my breast return to their former shape?
Unfortunately, the fact is that once the breasts have lost their original shape, nothing can really restore them to their original shape. Which is why there is a product out in the marked called Shock Absorber Sports Bra.

Do small breast also need support?
Although the need may not be as great as in the case of the larger breasts, still the research has found that even among 34As/75As the breasts movements are still high and it averages up to around 1.57inches (40mm) away from the resting place of the body which means that it can lead to breast sag. So even small breast still need the Shock Absorber Sports Bras

Doesn't running just naturally lead to tender and sore breasts?
Not supporting breast along with the high movements generated by the exercise is what leads to tender and sore breasts. However, if Shock absorber bra is used, then these outcomes are reduced.

Aren't ordinary bras good enough to reduce those movements?
Ordinary bras do reduce the movement of the breasts, however they only do so at the rate of 38%. Shock Absorber Sports bra on the other hand, reduces the breast movements by 74% and hence it is almost twice more effective.