Muscle pulling on bone builds bone, and weight-bearing exercise builds denser, stronger bones.
The more bone mass you build before age 25, the better off you will be during the years of gradual bone loss. Exercise can also help you maintain bone density later in life. If you already have osteoporosis, you might wonder whether you should exercise at all. You should speak to your doctor to learn what types of exercises you can safely do to preserve bone and to strengthen your back and hips. Keep in mind, however, the exercise alone can't prevent or cure osteoporosis.