When you use a set of muscles too much, you’re likely to strain the tendons (soft tissues) that connect those muscles to your bones. At first, pain or swelling may come and go quickly. But if you do too much too soon, your muscles may over-tire again. The strain may cause a tendon’s outer covering to swell or small fibers in a tendon to pull apart. If you keep pushing your muscles, damage to the tendons adds up and tendonitis develops. Over time, pain and swelling may limit your activities. But with your doctor’s help, tendonitis can be controlled. Both symptoms and your risk of future problems can be reduced.