Exercise the muscles of the shoulder joint

Nowadays, more and more people are suffering from the disease of periarthritis of the shoulder. This is because they have not done any exercise for a long time, which keeps their shoulders in a relatively stiff state. At this time, they are more likely to suffer from some diseases. Therefore, exercising the muscles of the shoulder joint is more important. Let us learn about the methods of exercising the muscles of the shoulder joint.

The movement of the shoulder joint is the coordinated movement between the joints. When the scapulohumeral joint moves, the scapulothoracic connection moves accordingly. This coordinated movement is called scapulohumeral rhythmicity. When the shoulder joint is abducted to 30° or flexed to 60°, the scapula does not rotate, which is called the static period. After this, the scapula begins to rotate. For every 15° of abduction, the shoulder joint rotates 10° and the scapula rotates 5°. The ratio of the two is 2:1. When the abduction is above 90°, the shoulder joint rotates 5° and the scapula rotates 10° for every 15° of abduction. The ratio of the two is 1:2.

The range of motion of the shoulder joint under normal circumstances is: flexion and extension 150°-170°, extension 40°-45°, abduction and extension 160°-180°, adduction 20°-40°, horizontal external rotation 60°-80° (or 45° sticking to the wall), horizontal internal rotation 70°-90° (or 70° sticking to the wall), horizontal flexion 135°, and horizontal extension 30°. In addition, the movement of the shoulder joint is based on the sternoclavicular joint as the fulcrum and the clavicle as the lever. Therefore, the range of motion of the shoulder joint can be increased due to the movement of the "shoulder-thoracic joint". These characteristics of the shoulder joint determine that the shoulder is prone to the diseases mentioned above.

The muscles involved in shoulder joint movement are mainly shoulder muscles, and shoulder joint movement requires the assistance of upper arm muscles. The movement of the shoulder joint must meet two conditions. One is that there must be good scapular muscles to keep the shoulder relatively stable. The other is that the humeral head and the glenoid cavity must be closely connected (this is mainly accomplished by the rotator cuff). Therefore, the skeletal muscles involved in shoulder joint movement do not simply supply joint power, but also play a major role in stabilizing the shoulder joint.

The shoulder joint is a ball-and-socket joint that can perform flexible multi-axial movements. Compared with the hip joint of the lower limb, the shoulder joint has a larger range of motion but poorer stability.

The shoulder joint can complete seven movements: flexion, extension, abduction, adduction, external rotation, internal rotation, and circumduction.

(a) Flexion: The muscles that cross the front of the coronal axis of the shoulder joint have the function of flexing the shoulder joint. Important muscles include the coracobrachialis, anterior fibers of the deltoid, clavicular portion of the pectoralis major, and short head of the biceps brachii. The range of motion in forward flexion is approximately 70°.

(ii) Extension: The muscles that cross behind the coronal axis of the shoulder joint have an extension effect. The main muscles involved are the latissimus dorsi, the posterior fibers of the deltoid, and the long head of the triceps brachii. During extension, the range of motion is limited by the joint capsule, the forearm, and the contact between the humeral head and the coracoid process, so it is smaller than the flexion range, approximately 60°.

(iii) Adduction: The muscles that cross below the sagittal axis through the humeral head can adduct the shoulder joint. The main muscles are the pectoralis major, latissimus dorsi and subscapularis. During adduction, the humeral head slides above the glenoid fossa and is hindered by the trunk, so its range of motion is very small, about 20°.

(IV) Abduction: The muscles that cross above the sagittal axis can abduct the shoulder joint. The main abductor muscles are the deltoid (middle fibers) and supraspinatus. When the shoulder joint is externally rotated, the long head of the biceps brachii also participates in abduction. When the shoulder joint is abducted, the humeral head slides downward to the glenoid fossa, so the range of motion is larger, about 90°.

(V) Internal rotation: The upper arm can rotate internally and externally along the vertical axis running through the center of the humeral head and the center of the humeral capitellum. Any muscle that crosses in front of the vertical axis from the inside (starting point) to the outside (end point) has the effect of internal rotation. The muscles that internally rotate are the latissimus dorsi, pectoralis major, subscapularis, and anterior fibers of the deltoid. During internal rotation, the humeral head slides posteriorly within the glenoid fossa, and the greater tuberosity and body of the humerus rotate anteriorly.

(vi) External rotation: The muscles that cross behind the vertical axis have an external rotation effect. The muscles that externally rotate are the infraspinatus and teres minor. During external rotation, the humeral head slides forward within the glenoid fossa, and the greater tuberosity and body of the humerus rotate posteriorly. When the upper limb is vertical, the range of rotational motion is the greatest, up to 120°.

This article will introduce in detail the methods of exercising the muscles of the shoulder joint. The muscle exercises in the shoulder joint are relatively simple, and the range of motion is relatively small. You just need to open your arms completely and then do a stretching exercise. You can also shake your head left and right.