Exercising to strengthen muscles strengthens the bones on which these same muscles attach.

Bones in the arm that holds the racquet of a professional tennis player are much larger and stronger than the bones in the other arm. The arm bones are bigger, denser and stronger in athletes who whose activities involve upper body strength, such as rugby, rock climbing, kayaking, and weight lifting, while runners were observed to have the lowest arm bone mineral density, even lower than that of the controls.

In one study, leg bone mineral density was highest in rugby players, whose activities included both running and strength training, but when bone density was corrected for body fat, runners had the strongest leg bones. So training is specific. When you strengthen your muscles, you also strengthen the bones on which muscles attach.

Several studies show that people with strong muscles also have stronger bones. All women will get osteoporosis if they live long enough. If you break a hip from osteoporosis, you have a 20 percent chance of dying from complications within a year. A study from Johns Hopkins shows that heart and lung fitness is not associated with stronger bones, but muscle strength and belly fatness are. The second study from Turkey shows that grip pressure is associated with strong bones.

Just exercising will not strengthen bones. Female marathon runners who stop menstruating because they do not eat enough food to meet their calorie requirements, develop osteoporosis even when they run more than 100 miles per week. A muscle can only be as strong as the bones on which it attaches. These studies show that people who store fat primarily in their bellies also tend to grow large muscles and have strong bones. High blood levels of insulin make a person store fat primarily in the belly, and call out insulin-like growth factor which cause muscles to grow.

Journal references on this article are in the Fitness section of my web site, listed below.