According to the general 2: 1 shoulder-arm rhythm, 120 glenohumeral joint abduction and 60 scapulohumeral rotation occur at the same time, resulting in 180 active shoulder abduction.

Principle 2

The elevation of sternoclavicular joint combined with the upward rotation of acromioclavicular joint leads to the upward rotation of scapula by 60 degrees at the completion of shoulder abduction.

Principle 3

When the shoulder is abduction, the clavicle retracts at the sternoclavicular joint.

Principle 4

When the shoulder is abduction, the scapula leans backward and rotates outward.

Principle 5

When the shoulder is abducted, the clavicle rotates backwards around its own axis.

Principle 6

When the shoulder joint is abduction, the single arm joint rotates outward.