Thank you for you question. This is a common query amongst patients in several areas of the body. Unfortunately, ptosis, or sag, of the breasts typically involves excess skin and deformation of the microscopic ligaments that maintain breast shape and structure. While strengthening the pectoralis major chest muscles will enlarge them, exercise typically has little effect on excess skin. Enough exercise will also decrease your overall body fat, which may decrease the size of the breasts. This could either improve or worsen the appearance of ptosis in the breasts depending on how the weight loss is distributed. Every individual is different. To truly address breast sag, surgical intervention in the form of a mastopexy, or breast lift surgery, would be required.