Shouler bursitis
Got deep, achy soreness that feels hot and swollen? Chances are you have shoulder bursitis, an inflammation of the bursa, a fluid-filled sac that provides a smooth surface for muscles and bones to glide over. "If you have two muscles aligned side by side and there isn't something between them to reduce friction, they wouldn't move," explains Dr. Gotlin. Normally these sacs, which are found in joints throughout the body, are filled with a small amount of fluid. Sometimes, though, when you overdo it (say, by throwing a ball or lifting something over your head repeatedly), the body responds by bringing more fluid to the bursa—and the swelling that influx produces is what's known as bursitis. "A bursa is like a balloon that's practically flat, and bursitis is the balloon being filled up with lots of water," says Dr. Gotlin.
The pain from bursitis is typically on the outside of your shoulder and it's made worse when using your arm above your head. Treatment is usually rest, ice or heat, and pain relievers, but your doctor may recommend physical therapy to stretch or strengthen the shoulder muscles and increase range of motion, and/or cortisone injections to reduce inflammation.