Anatomy of Motion

The shoulder is a particularly mobile area. There is needed numerous muscles to both stabilize and facilitate its movement.

Muscles connecting our arm to the body can be divided into 3 groups. While this is just one possible way to classify them, for the purposes of this video, the muscles are divided into functional muscles, general stabilizers, and humeral head stabilizers.

The first group consist of large, functional muscles and includes the pectoralis major, deltoid, and latissimus dorsi.

The second one comprises movement assistants and general stabilizers like pectoralis minor, biceps, coracobrachialis, part of the triceps, and teres major.

The third group consist of muscles dedicated to stabilize the head of the humerus: the subscapularis, supraspinatus, infraspinatus, and teres minor, collectively known as the rotator cuff ^[1] (you can find more information about it in this post: Rotator Cuff Injury).

Really important is finding a way to balance training among these groups. If one group becomes significantly stronger or weaker, the biomechanics of the arm will be compromised. Without strong and healthy stabilizers for the head of the humerus, the joint will move improperly, leading to bone and tendon degeneration. These stabilizers are responsible for maintaining proper alignment of the humerus and controlling its movement by causing translations. ^[2] Abnormal glenohumeral translations have been linked to pathological shoulders, contributing to pain and discomfort and potentially causing damage of encompassing structures. ^[3]

These muscles also play a role in a movement. Fox example, the supraspinatus muscle initiates the abduction movement of the arm by pulling the humeral head medially toward the glenoid cavity. An imbalance in the neural activation could easily cause a misalignment of the humeral head, resulting in impingement and other issues. ^[4]

General stabilizers are responsible for stabilization of joint and are created to prevent strains. They also assist larger muscles in moving the arm. If these stabilizers become shortened or stiff, the larger muscles cannot perform effectively, and the range of motion will be limited. When large functional muscles work without adequate stabilizer support, the shoulder becomes prone to injury.

So, if any of these groups fail to function properly, the appearance of pain is only a matter of time.

1. Plachel, Fabian, i in. „Risk Factors for Rotator Cuff Disease: An Experimental Study on Intact Human Subscapularis Tendons”. Journal of Orthopaedic Research, t. 38, nr 1, january 2020, s. 182–91. PubMed Central, https://doi.org/10.1002/jor.24385
2. Dal Maso, Fabien, i in. „Glenohumeral Translations during Range-of-Motion Movements, Activities of Daily Living, and Sports Activities in Healthy Participants”. Clinical Biomechanics (Bristol, Avon), t. 30, nr 9, November 2015, s. 1002–07. PubMed, https://doi.org/10.1016/j.clinbiomech.2015.06.016
3. Milgrom, C., i in. „Rotator-Cuff Changes in Asymptomatic Adults. The Effect of Age, Hand Dominance and Gender”. The Journal of Bone and Joint Surgery. British Volume, t. 77, nr 2, March 1995, s. 296–98
4. Sahrmann, Shirley, i in. „Diagnosis and Treatment of Movement System Impairment Syndromes”. Brazilian Journal of Physical Therapy, t. 21, nr 6, 2017, s. 391–99. PubMed, https://doi.org/10.1016/j.bjpt.2017.08.001