Muscle-strengthening exercises, or resistance exercises, pose some special challenges to people with osteoporosis. It's a good idea to keep yourself fit with exercise but caution and care is needed for those people with osteoporosis to avoid the possibility of injury or fracture.
Muscle-strengthening exercises are also called resistance exercises for the simple reason that they involve resistance, against gravity, or against a weight for instance. Lifting weights, using weight machines, working with exercise bands, and even Yoga and Pilates would be classified as muscle-strengthening exercises.
Try to exercise two or three days each week. If you are able, shoot for one exercise per major muscle group. Some of these major muscle groups would be upper and lower back, upper arms, abdominals and thighs.
"As you get started, your muscles may feel sore for a day or two after you exercise. If the soreness lasts longer, you may be working too hard and need to ease up. Exercises should be done in a pain-free range of motion."
http://forums.webmd.com/3/osteoporosis-exchange/forum/318?ecd=wnl_hbn_061410