From an article on why women need to weight train — heavy:
“Another reason women need to lift weights is to maintain bone density. Any women reading this who are over 40 years old have probably been emphatically prescribed copious amounts of calcium by their doctor. What the doc neglected to consider is the lack of stimulus necessary for your body to use valuable energy to build more bone. Maybe you should drop off a bunch of lumber in your doctor’s yard without mentioning why, and then get mad at him when he doesn’t use it to build a deck. He’s playing the same game with your body. Why would your body assume that you need more bone density if you never bear loads that would necessitate a stronger frame?”