always enjoy discussing this issue with women none the less.
Testosterone is the reason I am who I am, and (if you are a woman) the reason you are you. Facial hair and deeper voices are due to testosterone. It is also needed if an individual is wanting to "bulk up" significantly. Men have more testosterone than women. That is the reason men are more responsive to muscle growth. Women have lower testosterone levels than men. According to Bill Kreamer in "Essentials of Strength and Conditioning," women have about 15-20 times less testosterone than men. In fact, because fat takes up more space than muscle, when a women trains for strength, they tend to lose inches (building muscle/losing fat) not gain. Unfortunately, the women who ask me these types of questions have an altered perception of what weight lifting can do for them.
Their perception comes from what they see of women on the covers of bodybuilding magazines. Most of those women they see in those magazines, unfortunately, use anabolic steroids (synthetic testosterone) to achieve that muscularity. In fairness to women, many men use steroids as well to increase their testosterone levels, which leads to increase in total size and muscularity.
Picture this. As I stated earlier, what separates men from women? Testosterone. What if you take something that is not there (in this case testosterone) and add it in? What do you have? A man. Women who lift heavier weights without the use of steroids can obtain a more fit and firm figure easier than someone who lifts lighter weights or doesn't workout at all.
For a better idea of what weightlifting can do for a woman without altering testosterone levels, pick up those same magazines that have women "bodybuilders" and look at the pictures of the fitness or figure competitors. I have found that most find that to be a more suitable version of someone who is healthy and fit.