I've heard that swimming won't help prevent osteoporosis. Is this really true? I always get a good workout when I swim.

In order to stimulate bone growth, two things must happen. The muscles must contract and pull against the bone. This is called overloading. And overloading must be strong enough to actually physically deform the bone. This means that getting the heart rate up high enough to breathe heavy or sweat isn't enough.

Ground-reaction forces are the second thing needed to cause bone growth. This means force from the ground up through the foot and leg (weight-bearing activities) are required to maintain bone mineral density. During swimming, the muscles do contract against the bone, but there's no ground-reaction force.

Swimming is still a very good form of exercise. It can benefit your health in other ways. But you should alternate days with a weight-bearing activity such as walking or weight-lifting. More active exercise like jogging, tennis, volleyball, or basketball are also good.

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