Good question. The dead arm syndrome was a term first used by a well-known orthopedic surgeon in the early 2000s to describe the disabled throwing arm in athletes. It’s a complex series of events affecting the muscles of the shoulder and arm. The term syndrome is often used because there is a cluster or group of symptoms associated with the problem.
In the case of the dead arm syndrome, uncoordinated or deficient (weak, imbalanced) muscles around the scapula (shoulder blade) disrupt the kinetic chain. Each part of the shoulder complex from the scapula to the shoulder to the fingertips must work together in a complex series of coordinated motions. This is what we mean when we use the term kinetic chain.
Anything that alters the smooth transfer of energy along the kinetic chain can increase force produced by the shoulder. That’s when pain develops. Something has to give in order to keep up the pitching speed and control of the ball. In the throwing athlete that could mean impingement (soft tissues get pinched), labral or rotator cuff tears, or the development of a drooping throwing arm.
A drooping shoulder is just as it sounds. When the athlete is standing with the arm by his or her side, the shoulder of the throwing arm is noticeably lower than the other side. This occurs when the scapula on that side slides forward and tilts down over the rib cage. The arm follows with a forward and downward posture.
The solution to the problem is usually a special exercise program to strengthen and condition the shoulder and arm. In some cases, muscle fatigue from overuse is the cause of the problem. The athlete must be careful to avoid throwing too many pitches between practice and play. Too often, pitchers only count pitches during games and don’t realize that practice pitches count just as much.