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Electromyography of levator scapulae: new findings allow tests of a head stabilization model.

OBJECTIVE
Understanding the recruitment patterns of shoulder girdle prime-mover muscles will allow meaningful exploration of non-prime-mover neck muscle activity during arm and shoulder efforts. This study identifies exercises that isolate recruitment of levator scapulae from recruitment of upper trapezius. The exercises will be used for electromyographic experiments in which the head stabilizing roles of other neck muscles will be explored.


DESIGN
Right levator scapulae and upper trapezius were electromyographically monitored with indwelling, fine-wire, bipolar electrodes. Subjects performed isometric arm exercises and movements of the upper limb, shoulder and head.


SETTING
Electromyography facilities of the department of Anatomical Sciences of the State University of New York at Stony Brook were used.


PARTICIPANTS
Six adult subjects participated; one had reduced shoulder girdle mobility and a history of multiple shoulder separations.


MAIN OUTCOME MEASURES
Raw electromyographic data were scored visually on a scale from 0 to 4, with 4 being the signal observed in a maximal voluntary contraction.


RESULTS
All subjects recruited levator scapulae alone during arm extension. Only the subject with reduced shoulder mobility recruited levator scapulae during scapular plane arm elevation and arm abduction.


CONCLUSIONS
The levator scapulae torque to be counteracted in arm extension produces ipsilateral rotation, lateral flexion and extension of the neck; trapezius rotates the head contralaterally during scapular plane arm elevation. These distinct and relatively simple cases (one shoulder girdle prime-mover affecting head posture at a time) are appropriate exercises for experimental exploration of the recruitment patterns of potential head stabilizers during arm/shoulder efforts.