Rotator cuff tendinitis is most common in young athletes and middle-age people. It occurs when a normal, healthy rotator cuff tendon is injured or inflamed, often as a result of a repetitive overhead activity (for example, painting, tennis, swimming, baseball, volleyball, or weightlifting). 1
https://www.verywellhealth.com/signs-and-symptoms-of-a-rotator-cuff-tear-2549777

