I've played tennis for years. Lately, I've had pain in my shoulder when I serve. What could be causing this?

You'll need to see a doctor to find out for sure. The doctor will want to do a thorough physical exam of the shoulder to check for muscle weakness or tenderness. He or she may also order tests such as magnetic resonance imaging (MRI) to identify the cause of your symptoms.

Your symptoms may be coming from a tear in the rotator cuff or inflammation of the tendons that make up the rotator cuff (tendinitis). When your doctor finds the source of the problem, you can move forward with treatment.