Trapezius Muscle Activation During Bilateral Scapular Retraction and Shoulder External Rotation Under Kinetic Chain and Unstable Surface Conditions

Trapezius Activation During Bilateral Scapular Retraction With Shoulder External Rotation: The Incorporation of Knetic Chain and Unstable Surface

This study aims to investigate the effects of performing the Bilateral Scapular Retraction with Shoulder External Rotation (BSR-SER) exercise under kinetic chain involvement and unstable surface conditions on trapezius muscle activation. Surface electromyography (EMG) will be used to assess the activity levels of the upper, middle, and lower trapezius muscles. The goal is to determine whether integrating kinetic chain elements and instability can optimize muscle activation patterns in healthy individuals during a commonly used scapular rehabilitation exercise.

Maintaining muscular balance among the scapular stabilizers is crucial for optimal shoulder function. The Bilateral Scapular Retraction with Shoulder External Rotation (BSR-SER) exercise is frequently used in clinical rehabilitation to activate the lower trapezius while minimizing upper trapezius activity. Although this exercise is widely practiced, the effects of performing it under kinetic chain conditions (such as squat and lunge positions) and on an unstable surface have not been thoroughly explored.

This study will examine how adding kinetic chain involvement and instability influences the electromyographic activity of the upper trapezius (UT), middle trapezius (MT), and lower trapezius (LT) muscles during the BSR-SER exercise. Twenty healthy participants will perform the exercise in various lower extremity positions (standing, squat, lunge) and on both stable and unstable surfaces using a BOSU® ball. EMG data will be collected using a wireless surface EMG system and analyzed in terms of percentage of maximal voluntary isometric contraction (%MVIC).

The results of this study may provide valuable insights into the optimization of scapular stabilization exercises and guide clinicians in designing more effective shoulder rehabilitation programs by incorporating kinetic chain principles and unstable surfaces.

Inclusion Criteria:

• Age between 18 and 35 years
• Body Mass Index (BMI) less than 30 kg/m²

Exclusion Criteria:

• Engaging in more than 6 hours per week of overhead sports or upper extremity strength training
• History of surgery in the spine, lower extremities, or upper extremities
• Experiencing pain in these regions within the past 6 weeks
• Having a rheumatologic, systemic, or metabolic disease