A good program includes aerobic exercise, like running, walking or biking, to improve endurance and oxygen uptake, stretching to maintain range of motion and flexibility, and strength training to maintain muscle and bone mass. Osteoporosis is one of the most common and debilitating diseases of aging, but it doesn't have to be. With adequate calcium intake and regular exercise, most people can maintain strong bones well into their 80s or even 90s. As you stress the bones in weight training, the body reacts by maintaining as much mineralization as possible. Beyond age 40, athletes start to lose the ability to add muscle mass.
Weight training offers more than just osteoporosis prevention.
Training also helps control weight gain, and a recent study at Harvard University suggests that it helps combat depression. If you have any physical disabilities or if you've been sedentary, get your physician's recommendations before starting a program. Consider paying for a few sessions with a personal trainer if you've never done resistance training. A certified trainer can help you get the most from your workouts with less chance of injury. Start with very light weights, increasing the weight a little each week.