新規理学療法ジャーナル

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Isometric Contraction of Scapular Muscles Activities during Horizontal Abduction and Adduction of the Shoulder

Tomohito Ijiri, Ryoichi Takagi and Toshiaki Suzuki

Background: Scapular stability is important for shoulder movement; however, the mechanism of scapular stability remains unknown. In addition, activities of scapular muscles have been only evaluated during shoulder elevation, but not extensively observed those of other shoulder movements. We investigated muscle activity, including scapular muscle activity, during horizontal abduction and adduction of the shoulder joint.

Methods: Eighteen healthy men without orthopedic or neurological abnormalities participated in this study. Muscle activity was measured during horizontal isometric abduction and adduction of the shoulder joint in the sitting position. Measurements were conducted in three positions horizontal adduction at 0°, 45° and 90°, and external loads were set at 3, 5 and 10% of each subject's body weight. External load was added to the direction of horizontal abduction on horizontal adduction task and the direction of horizontal adduction on horizontal abduction task. Surface electromyography was used to collect raw data during the task. Based on scapular movements during shoulder motion, the measured muscles were classified as agonist muscles of the glenohumeral joint, and agonist and antagonist muscles of the scapulohumeral joint.

Results: The same patterns of muscles activities were identified during horizontal abduction and adduction in all positions. Electromyographic activities of agonist muscles of both the glenohumeral and scapulothoracic joints became higher with greater load; however, activities of antagonist muscles of the scapulohumeral joint did not show statistical significance.

Conclusion: Most scapular muscles engage during isometric contraction, and the high activating muscles were changed by the direction of shoulder movement. We have to evaluate the scapular muscle activities individually in consideration of this finding.