Large breasts can be very uncomfortable for a person's frame to support. The weight tends to drag on the neck and shoulders when upright. When on ones back, they can drag on the skin of the chest and shoulder. There are other sources for pain in these regions, breast reduction is not always the solution. I advise my patients to check out what water buoyancy does to their discomfort.
Breasts tend to float.
Breast reduction is an operation where the extra glands, fat, and skin are removed and the breasts restored to a more natural proportion. Wound shortening techniques try to limit the length and severity of scars. Supportive bras have some value with wide straps that distribute the weight across the shoulders. I am not certain how exercise will help the problem. Some insurance companies recognize the short person as having different limits as the larger woman for breast reduction qualifications.