What causes shoulder pain?

Shoulder pain is a common ache in the U.S.: By some estimates, as many as 67% of people experience shoulder discomfort at some point over the course of their lives. The most mobile joint in your body, the shoulder is made up of bones held in place by muscles, tendons, and ligaments. They're all designed to work together to allow the shoulder to move freely in many different directions. This allows you to do everything from raising your arms over your head to throwing a baseball and scratching your back. "Unfortunately, this mobility comes at the expense of stability," and that leaves the shoulder vulnerable to injury, says Clifford Stark, medical director of Sports Medicine at Chelsea in New York City. Factor in the wear and tear of everyday life and it's easy to see why you're shouldering so much pain.

You'll need to consult your doctor for a formal diagnosis of your shoulder pain. That visit will include a physical exam, and possibly an X-ray, MRI, or ultrasound, or you may even do a physical therapy right off the bat, Dr. Stark says.

Of all the reasons you can have shoulder pain, injury to your rotator cuff is the most common-in a recent study, two-thirds of people with shoulder pain had a rotator cuff problem. A group of muscles and tendons that attach to the bones of the shoulder joint, the rotator cuff keeps the ball of your upper arm bone centered in your shoulder socket and also helps you raise and rotate your arm.

Doing the same motion over and over again can lead to inflammation of the rotator cuff tendons, also called tendonitis, which can cause shoulder pain. "The rotator cuff is like a tire-with aging or frequent use it gets thinner and thinner and eventually wears down," says Robert Gotlin, a sports and spine physician in NYC and an associate professor of rehabilitation medicine and orthopedics at the Icahn School of Medicine at Mount Sinai. With tendonitis, shoulder pain is often mild at first and only noticeable when you move the joint; after a while, they can become more severe and occur all the time.