Your shoulders, as the most mobile joint in your body, bear a lot of load during upper-body exercises and daily activities. They’re always working to keep your arms stable while you’re performing tasks such as lifting weights, carrying heavy groceries, or swimming. However, if you feel pain in your shoulders when you lift a weight overhead or while playing some sports such as tennis or swimming, it may be time to see your doctor. You may have shoulder impingement, which is treatable but requires close monitoring and possibly a few sessions with a physical therapist or a doctor. Muscle imbalances around the shoulder are almost always present in patients with shoulder impingement, resulting in abnormal biomechanics.