The American College of Sports Medicine (ACSM) now has fitness guidelines specific to weight training for people over 50.

The advice: perform such exercises 2 to 3 times a week to condition all of the major muscle groups — arms, legs, shoulders, and trunk.

The goal is to lift a weight that’s heavy enough to achieve 10 to 15 repetitions per session before the muscles become fatigued.

Most older individuals are well aware that they need regular aerobic exercise, such as walking, swimming, or running, to strengthen their heart and lungs and tone their bodies, but many dismiss weight training (also called resistance training) as an activity predominantly for the young or the vain. However, it is the only type of exercise that can substantially slow, and even reverse, the declines in muscle mass, bone density, and strength that were once considered inevitable consequences of aging.

Unlike aerobic, or endurance, activities, which improve cardiovascular fitness and require moving large muscle groups hundreds of times against gravity, weights provide so much resistance that muscles gain strength from only a few movements.

You shouldn’t experience pain while lifting weights, but it’s normal to feel some soreness the next day. Experts believe that as muscles are challenged by the resistance of a weight, some of their tissue breaks down; as the muscles heal, they gradually increase in strength and size.

Although muscles should be worked until they are fatigued, common sense will dictate when it’s time to stop.

If you feel joint or nerve pain, or are putting a tremendous amount of strain on any part of the body, you’re probably going overboard and can harm yourself. Because strains, sprains, and tissue damage can take weeks or even months to heal, preventing injury should be a priority.