In addition to cardiovascular exercise, you need to do 30 minutes of strength training three times a week. As a rule, muscle mass begins declining around age 40, and picks up speed after about age 50.

The rate of muscle loss then really accelerates, outpacing muscle gain. By the time people reach 70, they are often so weak they can’t even pick up a bag of groceries.

Once upon a time, we thought that there was nothing to be done about this. But we now know that muscle loss isn’t inevitable. In recent years, studies conducted in nursing homes have shown that strength training combats “muscle wasting” in old age.

Strength training, known also as “resistance training,” is anaerobic exercise, which means it does not require the infusion of extra oxygen as aerobic exercise does.

Instead of added oxygen, your body uses glycogen, which is a form of energy that it stores.

Strength training also builds up lean muscle mass, which helps your body burn fat more efficiently.

Exercises should involve all of the muscle groups: legs, hips, chest, back, abdomen, shoulders, and arms. These activities should make your muscles work harder than they are accustomed to during your daily activities.