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Effect of Shoulder External Rotation on EMG Activity of the Scapular Upward Rotators During Arm Elevation

  • Journal of the Korean Society of Physical Medicine
  • Abbr : J Korean Soc Phys Med
  • 2015, 10(4), pp.113-121
  • Publisher : The Korean Society of Physical Medicine
  • Research Area : Medicine and Pharmacy > Physical Therapy > Other physical therapy

Jung, Do-Young 1 원종혁 2

1중부대학교
2중부대학교 물리치료학과

Accredited

ABSTRACT

Purpose: The purpose of this study was to determine the effect of shoulder external rotation on muscle activities of the scapular upward rotators during arm elevation. Methods: Nineteen healthy subjects with no medical history of shoulder pain or upper extremity disorders were recruited for this study. Electromyography (EMG) was used to measure the muscle activities of the serratus anterior (SA), upper trapezius (UP), lower trapezius (LT) and infraspinatus (IS) muscles during arm elevation. The EMG activities were recorded while the subjects performed 90° arm elevation with three different arm positions; palm down (PD), neutral position (NP), and palm up (PU). While seated in a chair, the subject was asked to raise the upper extremity in the sagittal plane in random order. Subjects performed 90° arm elevations in three trials at each arm position. The mean EMG activity normalized by the maximal voluntary isometric contraction was analyzed across three arm positions. Repeated measures one-way ANOVA and the post hoc Bonferroni tests were used to determine the differences in muscle activities among the three arm positions. Results: The EMG activities of the SA and IS were significantly greater in the PU condition than in the other conditions during arm elevation. No significant difference was noted between the NP and PD conditions during arm elevation. Conclusion: These results suggest that shoulder external rotation (palm up position) can be used to activate the SA. Therefore, we recommend a scapular protraction exercise in the palm up position for strengthening the SA.

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