Playing tennis isn't good for your muscles and mind alone; it has a positive impact on your bones as well. Exercising regularly can increase your peak bone mass and can slow the rate of bone mass loss over time. According to the National Institutes of Health (NIH), bone mass peaks around age 30 and begins to decline after that. You can maximize your bone mass prior to that age through exercise, and continuing to exercise after 30 can slow the rate of bone loss [source: NIH Osteoporosis and Related Bone Diseases National Resource Center].
The NIH also points out that exercise improves coordination, flexibility and muscle strength, which can help prevent falls and injuries that can damage fragile bones.
The best exercises for building bone strength and mass are exercises that involve weights. But that doesn't mean you have to be lifting something -- your body, and the resistance of gravity against it, is often enough to give you the weight-bearing exercise needed to support bone health. The NIH names tennis as one of the weight-bearing activities well suited to building strong bones.