Almost everyone should lift weights. Weight lifting strengthens bones, muscles ligaments and tendons, increases coordination for tasks requiring strength, and gives confidence and mobility to disabled people. Just exercising doesn't do much to strengthen muscles. If it did, marathon runners would have the largest muscles. To become strong, you have to exercise your muscles
against progressively greater resistance, such as lifting heavier weights.
Just exercising doesn't strengthen bones either. Female marathon runners sometimes stop menstruating and lose tremendous amounts of bone, even though they may run more than 100 miles a week. To regain bone, they have to eat more food which will usually start them menstruating again, or they may need to take estrogen.
People with muscle and nerve diseases can also benefit from lifting weights. They may be unable to work out as long or as hard as a healthy person and they take longer to recover from their workouts. However, if they stop exercising when their muscles feel heavy or hurt and they take off when their muscles feel sore, they can make dramatic increases in strength.
Anyone starting a weight training program should be guided by an experienced instructor. Exercise with machines two or three times a week, never on consecutive days. On each exercise, use the heaviest weight you can lift comfortably eight or ten times in a row. Then allow at least 48 hours for your muscles to recover. Do not lift if they feel sore.