EMG OF SHOULDER MUSCLES DURING REACTIVE ISOMETRIC ELASTIC RESISTANCE EXERCISES

Area of Science:

• Biomechanics
• Rehabilitation Science
• Exercise Physiology

Background:

• Shoulder isometrics are a cornerstone of early-stage rehabilitation.
• Current methods rely on subjective force perception, limiting precision.
• Standardizing isometric exercises using elastic resistance offers objective % maximum voluntary contraction (%MVC) prescription.

Purpose of the Study:

• To measure electromyographic (EMG) activity during shoulder isometric exercises.
• To determine %MVC at varying elastic resistance band elongations.
• To test the hypothesis that increased band elongation proportionally increases shoulder musculature %MVC.

Main Methods:

• Healthy subjects (n=8) performed isometric shoulder flexion, external rotation, and abduction.
• Surface EMG recorded anterior deltoid, middle deltoid, and infraspinatus activity.
• Subjects incrementally increased distance from an anchored TheraBand®, varying elongation (50-250%) and color (yellow to blue).

Main Results:

• EMG activity for shoulder flexion and external rotation increased significantly with band elongation and color.
• Abduction showed increased middle deltoid activity with elongation and color.
• Force output increased with elongation and color, with distinct increases from red to green to blue bands.

Conclusions:

• Elastic resistance band elongation and color can accurately prescribe shoulder isometric exercises.
• This method allows for objective %MVC-based prescription in clinical settings.
• Therapeutic isometrics can be precisely controlled by manipulating band resistance and length.