Many people are talking about a relationship between weight training and decreasing breast size in women , It is one of the most common myths about weight training. This misconception has prevented many women from incorporating weight training into their quests to lose weight and firm up their bodies- a path that inevitably leads to failure as weight training is without question the most effective way to really tone up and develop a tight body. What about the prospect of becoming flat chested? To answer that I can honestly say that unless you plan on starving yourself or using anabolic steroids, women have little to worry about in terms of their breasts getting smaller from weight training. In fact most tend to see a slight increase over time! Weight training properly executed with sufficient intensity, adequate rest and nutrition will bring about an increase in muscle size of any part of the body that is being worked. This holds true whether it be it the pectoralis muscles of the chest (or pecs as many call them) or the muscles of your arms and legs. The way that this process (hypertrophy) works is that individual muscle fibers will get bigger (slightly bigger, that is, you won’t see mountains of muscle sprout on a woman without the use of anabolic steroids as it takes men with ten times more testosterone, years upon years to develop a muscular physique) or they will split and then get slightly bigger. The fibers of your pectoral muscles are all constituents of skeletal muscle whereas breast tissue is made up of sex specific adipose tissue (fat), ligaments, connective tissue and mammary glands. There are no skeletal muscle fibers found in the breasts as they simply sit directly over the pectoralis muscles. Weight training therefore can have no direct effect on them whatsoever. Breasts thus cannot hypertrophy or get larger due to weight training, but by increasing the size (slightly, ladies) of the pectoral muscles under the breasts there will be a natural increase in overall chest size. It may then appear that the breasts look a bit larger as they will stand up a bit more (which, is something most women would not mind) but the actual size and composition of the breasts themselves will not change. A study conducted in the University of Arizona back in 1985 confirmed this phenomenon in a 21 day study that used concentric and eccentric contractions with a specialized chest exercise machine. After the three week program researchers found no changes whatsoever in the size, shape or volume of the breasts of the women participating after extensive scientific measurement. So what about those flat chested women in the magazines with thickly developed chest muscles and no breasts? First off all the female bodybuilders that we typically see use drugs to develop unnatural degrees of muscular development and body fat reduction and do not represent in any way what a regular woman would look like if they weight trained. The size and shape of breasts in a healthy woman is fairly resistant to change as long as there are normal conditions of hydration and food availability, but in cases of extreme under nutrition (for example the type of starvation diets that bodybuilders undergo to get that lean and vascular look or someone with an eating disorder like bulimia or anorexia) where there is a severe reduction of body-weight and overall body fat the breasts which have a high proportion of fat, will shrink. In the case of the female bodybuilders you see the dense muscle tissue in their chest area and no breasts and the assumption is erroneously made that somehow the weight training made their breasts go away whereas the truth is that the shrinkage came from the reduction in body fat and nothing else. Source
