(That’s the bump on top of your shoulder where your shoulder blade and collarbone meet.)Īll the more reason to know how the shoulder muscles tasked with supporting this vital joint are supposed to function. Even more startling: When researchers at New York-Presbyterian/Columbia University Medical Center performed MRIs on people who reported no complaints of shoulder pain, they discovered that 82 percent of the adults tested showed signs of arthritis in the acromioclavicular (AC) joint. Broad, defined shoulder muscles are like a billboard declaring, “I WORK OUT! But if you don’t take care of this complicated joint, that little sign can quickly turn into “ROAD CLOSED!”Īs many as two-thirds of people will experience shoulder problems during their lifetime, according to a Dutch research review.