Even if you don't want to exercise in public or spend the money to join a gym, you can build strength at home. A set of handheld dumbbells at 1, 2, 5, 8, and 10 pounds can cost as little as $50, says James M. Rippe, M.D., author of Fit over Forty (Quill, 1996).

The principle behind weight training is to add resistance to your body's natural movements so muscles get stronger. Inexpensive bands, cables, and exercise balls -- even soup cans, paperbacks, sand-filled socks, or water-filled jugs -- can do the job. A pint is a pound, so a quart would be 2 pounds, a half-gallon 4 pounds, and a gallon 8 pounds.

Below are some recommended exercises you can do at home.

According the American Council on Exercise (ACE), the nonprofit organization that sets standards for certification of fitness trainers, one set of 8-12 repetitions, working the muscle to the point of fatigue, is usually sufficient to begin with. When you are able to perform 12 repetitions of an exercise correctly (without cheating), you may increase the amount of resistance by 5 percent to 10 percent to continue safe progress. Conditioned individuals may want to increase the weight, number of sets, or the frequency or duration of their workouts to increase muscle mass.

1. Bent row. Place right hand and knee on a bench so that your back is parallel to the floor. Grasp a dumbbell with your left hand and pull straight to your chest. Lower dumbbell. Repeat and switch sides. Keep hips level, back straight, and elbow close to your body. Works the opposing muscles: upper back, biceps, and rear shoulders.

2. Dumbbell bench press. Lie face up on a bench, holding a weight directly above each shoulder. Slowly lift upward and return. Repeat. Avoid locking elbows and don't rotate wrists. Works chest, triceps, and front shoulders.