Research Review: Electromyographic analysis of infraspinatus and scapular muscles during external rotation with different weight loads and positions.

By David Boettcher MSc, BA, NASM CPT, PES& CES & NPTI

Edited by Brent Brookbush DPT, PT, COMT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation:

Sasaki, S., Kenmoku, T., Otera, A., Miyajima, G., Nagura, N...Takahira, N. (2017). Electromyographic analysis of infraspinatus and scapular muscles during external rotation with different weight loads and positions. Journal of orthopaedic science, 28(1), 154-158 - ARTICLE

Introduction:

Resisted external rotation is commonly used as a strengthening exercise for the posterior rotator cuff musculature (1,2). Lighter loads are often recommended with the intent of optimizing form and reducing recruitment of synergistic muscles. This 2017 study by Japanese researchers, compared the electromyographic (EMG) activity of the infraspinatus, posterior deltoid, upper trapezius and bicep brachii during seated and supine resisted external rotation with varying loads. The study findings suggest seated external rotation using a higher load, with 0º of shoulder abduction and 90º of elbow flexion, may result in the greatest infraspinatus activity.

Figure-1-1b-Rotator-Cuff_Side-View Musculature surrounding the shoulder

Study Summary

Study DesignObservational/Comparative study
Level of EvidenceIII - Evidence from non-experimental descriptive studies, such as comparative studies, correlation studies, and case-control studies
Participant CharacteristicsDemographics

  • Number of participants: 16

    • A total of 30 shoulders were tested

  • Gender: 8 males, 8 females
  • Male mean age: 26.1
  • Female mean age: 25.9

Inclusion Criteria:

  • All participants were asymptomatic, with no pain in the shoulder tested.

Exclusion Criteria:

  • Shoulders with any pre-existing pain or pathology.

Methodology

  • Electrodes were inserted into the infraspinatusposterior deltoid, upper trapezius, and bicep brachii.
  • Participants were instructed to perform external rotation with 0º of shoulder abduction and 90º of elbow flexion.
  • Participants performed 8 different testing conditions.

    • A seated position using:

      • no weight
      • .5-kilogram
      • 1-kilogram
      • 2-kilograms

    • A supine position using:

      • no weight
      • .5-kilogram
      • 1-kilogram
      • 2-kilograms

  • The isometric external rotation