You’re already familiar with the way that exercise strengthens muscles. When you lift free weights with your arms, for instance, your arm muscles respond by building more muscle to prepare themselves for similar stress in the future. Over several weeks of such exercise, you will notice a firm mound of biceps where once there was level terrain. In a similar way, your bones strengthen themselves in response to certain kinds of exercise. When bones grow stronger and denser you won’t be able to detect it visually as you can with muscles. This strengthening is nevertheless particularly important as you grow older, because it can help prevent—or lessen the effects of—  the bone-wasting condition called osteoporosis.

A lot of factors can affect your bone strength, including diet, sex hormones, heredity, physical activity and medications. Osteoporosis is more common in women, who can experience rapid bone loss as early as age 40, when estrogen production drops in menopause.

Osteoporosis can occur in men, too, but typically not until age 65. Strength training exercises such as free weights, weight machines and resistance bands will help to slow the loss of minerals in your bones. The same goes for weightbearing aerobic exercise—that is, activities such as walking and stair climbing, which raise your heart rate while your bones and muscles work against the force of gravity.

In response to these forms of exercise, chemicals are released that tell your bones to prepare themselves for more of the same type of work, and therefore your bones become denser and stronger.

Conversely, if you are physically inactive as you age, your bones may lose density and weaken. While all bones can weaken, you become particularly vulnerable to fractures in your spine, hip and wrist.

Not only will exercise strengthen your bones outright. Your bones gain protection in other ways as well. For instance, because exercise will improve your balance and strengthen your muscles, you reduce your chances of breaking bones in a fall.

Talk to your doctor about your plans to fight osteoporosis with exercise. Your doctor or a physical therapist will want to recommend an exercise program that’s designed specifically for your physical condition, taking into account your general health and your degree of bone loss. If you have experienced some bone loss, avoid jarring exercises that could cause compression fractures—jogging and jumping, for instance. Also avoid exercises in which you bend or twist the waist, which could injure your spine.

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