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Written By Jim Moran, PT, Shoulder Specialist and Tim Terry, DPT Student, Research & Education Did you know that one of the most common shoulder stretches could end your playing career? This stretch is typically performed during a pre-throwing stretching routine under the assumption that it will improve throwing velocity by increasing the flexibility of the shoulder into external rotation. Stretching the shoulder into external rotation at 90 degrees (See Image) should be avoided because it targets the already loose ligaments of the anterior capsule. Further stretching the anterior capsule will lead to shoulder instability and highly increase the probability of injury.

A healthy shoulder relies on a delicate balance between static and dynamic stability in the glenohumeral (shoulder) joint. Static stabilizers of the shoulder consist of the joint capsule, labrum, and the glenohumeral ligaments that attach to the labrum. These stabilizers create a negative pressure (suction) within the glenohumeral joint that keeps the head of the humerus centrally located. The dynamic stabilizers consist of the rotator cuff, and the scapular muscles. The larger scapular muscles control scapular stability, glenoid position, and produce forces necessary for shoulder movements. The rotator cuff muscles keep the head of the humerus centrally located throughout the entire range of motion1. Over the course of a playing career, the shoulder undergoes adaptive changes as a result of the extraordinary forces produced during the throwing motion. The dominant (throwing) shoulder develops an increased range of motion (ROM) into external rotation and decreased ROM into internal

rotation when compared to the non dominant shoulder2. The increased ROM into external rotation is a direct result of the progressive loosening of ligaments within the anterior capsule. This ligament laxity not only affects shoulder ROM but also increases the likelihood of glenohumeral translation (movement of the humeral head in the socket)3. On the flip side, the decreased ROM into internal rotation, also referred to as GIRD (glenohumeral internal rotation deficit) can be attributed to tightness in the posterior capsule and cuff muscles (i.e., infraspinatus, teres minor). This posterior capsule and cuff tightness is also hypothesized to increase humeral head translation which is the chief cause of injury to the labrum and rotator cuff tendons4. As leaders in the field of arm care, we feel a responsibility to inform the baseball community about the dangers of this widely used stretch. The anterior capsule is already loose because of the forces created by repetitive throwing and should not be further stretched as this will create instability. Stretching into external rotation at 90 degrees should only be performed by a medical professional after an injury or surgical procedure to recover lost ROM. Instead of the aforementioned stretch, the tightness in the posterior capsule and cuff is what needs to be addressed. Crossover Symmetry will be launching our new posterior capsule and cuff stretching routine in Part 2 of this shoulder stretching segment.

1. Mahaffey, B., Smith, P. (1999). Shoulder instability in young athletes. American Family Physician. 2. Seroyer, S., Nho, S., Bach, B., Bush-Joseph, C., Nicholson, G., Romeo, A. (2009). Shoulder pain in the overhead throwing athlete. Sports Health: A Multidisciplinary Approach vol.1:108-120. 3. Ninos, J. (2001). Chain reaction: a tight shoulder posterior shoulder. Strength and Conditioning Journal vol. 23(5): 74-75. 4. Andrews, J., Wilk, K., Reinold, M. (2009) The Athlete's Shoulder

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