The three phases of
flexion
The first phase of flexion: 0-50/60′
The muscles involved are these:
. the anterior clavicular fibres of the cleltoid
. the coraco-bracbialis
. the superior clavicular fibres of the pectoralis major
This movement of flexion at the shoulder is limited by two factors:
tension developed in the coraco-humeral ligament.
resistance offered by teres minor,teres maj or and infraspinatus.
The second phase of flexion: 60-1 20″
The shoulder girdle participates as follows:60o rotation of the scapula so that the glenoid cavity faces superioly and anterioly
. axial rotation mechanically linked at the sterno-costo-clavicular and acromio-clavicular joints, each joint contributing 30′.
The muscles involved are the same as in abduction: the trapezius and the seratus anterior .
This flexion at the scapulo-thoracic joint is limited by the resistance of the latissimus dorsi and the inferior fibres of the pectoralis major .
The third phase of flexion: 120-180′
The raising of the upper limb is continued by the action of the deltoid, the
supraspinatus, the inferior flbres of the trapezius and the seratus anterior. When
flexion is checked at the shoulder and in the scapulo-thoracic joints, movement
of the spinal column becomes necessary. If one arm is flexed, it is possible to
complete the movement by shifting into the position of maximal abduction and
then bending the spinal column laterally. If both arms are flexed, the terminal
phase of the movement is identical to that of abduction, i.e. exaggeration of
the lumbar lordosis by the lumbar muscles.