Scapulohumeral rhythm

In the third phase (150 to 180 degrees) the spinal column is displaced laterally by the action of the contralateral spinal muscles. Bilateral abduction would require an exaggeration of the lumbar lordosis, because the spinal column would be otherwise synergistically balanced. These combined motions are known as the scapulohumeral rhythm,... 

The scapulohumeral rhythm is a free-flowing and synchronous movement of the scapula and humerus. During abduction, the scapula rotates as the humerus elevates. For every 15 degrees of abduction, humeral elevation accounts for 10 degrees and scapular rotation accounts for 5 degrees. Dysfunction of humeral elevation or of scapular rotation can disturb this rhythm and interfere with shoulder function. Dysfunction of clavicular motion can also interfere with this rhythm. 

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See also in sourсe #XX -- [ , ]

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