Shoulder bursitis
If you experience deep, achy soreness that feels a bit hot and swollen, then you might have shoulder bursitis, and inflammation of the bursa, which is a fluid-filled sac that comes with a smooth surface for muscles and bones to glide over more easily.
“If there are two muscles aligned side by side, but there’s nothing between them to reduce friction, then they wouldn’t be moving” as Dr. Gotlin explained.
Usually, these sacs, which can be found in joints throughout the body, have a very small amount of fluid within them. At times, when you overdo it, maybe because you vigorously threw a ball or you lifted something over your head repeatedly, the body will respond by bringing more fluid to the bursa. The area will become swelled, and that’s what’s known as bursitis.
