The vast majority of women simply do not produce enough testosterone to build big muscles. As you increase the amount of lean muscle you have your limbs will appear longer, you will burn more body fat, and your limbs will become slimmer. You will protect against osteoporosis and be far more capable in life as a whole. From the age of about 30 we all lose muscle and therefore tone unless we do something about it. In order to remained toned you have to perform more than just cardiovascular exercise (running etc).
