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Related Experiment Videos

Optimal normalization tests for shoulder muscle activation: an electromyographic study

B T Kelly1, W R Kadrmas, D T Kirkendall

  • 1Division of Orthopaedic Surgery, Sports Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA.

Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society
|July 1, 1996
PubMed
Summary

This study identified four standard manual muscle testing positions for maximal neural activation of eight key shoulder muscles. These positions provide reliable reference values for normalizing electromyography data in future research.

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Area of Science:

  • Kinesiology
  • Biomechanics
  • Human Movement Science

Background:

  • Accurate comparison of electromyographic (EMG) data across muscles and subjects requires data normalization.
  • Maximal voluntary contraction (MVC) is a common method for EMG normalization, but standardized testing positions are needed.

Purpose of the Study:

  • To identify specific manual muscle testing positions that elicit maximal neural activation (integrated EMG) in the supraspinatus, infraspinatus, subscapularis, pectoralis major, latissimus dorsi, and deltoid muscles.
  • To establish standardized reference values for EMG normalization in shoulder muscle studies.

Main Methods:

  • Eight shoulder muscles (3 rotator cuff, 5 synergists) were studied in nine subjects using indwelling and surface EMG electrodes.
  • Subjects performed 27 isometric contractions to identify positions of maximal neural activation for each muscle.

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Main Results:

  • Four distinct testing positions were identified that produced maximal neural activation for all eight shoulder muscles studied.
  • Specific positions were determined for supraspinatus, anterior deltoid, middle deltoid, infraspinatus, posterior deltoid, subscapularis, latissimus dorsi, and pectoralis major.

Conclusions:

  • The identified positions serve as standardized protocols for eliciting MVC in these shoulder muscles.
  • These standardized positions facilitate reliable EMG data normalization for future dynamic and isometric shoulder studies.