Selective Activation of the Infraspinatus During External Rotation Exercises in Participants with Rounded Shoulder Posture: Comparison of Three Common Exercises and Muscle Architecture-Based Exercise.

Background and Objectives: The infraspinatus muscle is critical for shoulder stability and external rotation, yet achieving selective activation during exercises remains challenging. This study explores the effectiveness of a novel muscle architecture-based position (MABER) compared to traditional exercises in individuals with rounded shoulder posture. Materials and Methods: This prospective, cross-sectional study evaluated the selective activation of the infraspinatus during external rotation exercises in participants with rounded shoulder posture. Thirty-two participants (17 males and 15 females) were recruited. Electromyographic (EMG) activity of the middle trapezius, posterior deltoid, and infraspinatus muscles in the dominant limb was recorded during four exercise positions: standing external rotation (SER), side-lying external rotation (SDER), scapular plane external rotation (SPER), and MABER. Results: MABER produced the highest infraspinatus activity (p < 0.001), while the lowest activity was observed during SPER (p < 0.001). The SER position generated higher posterior deltoid activity compared to other positions (p < 0.001). The SDER position demonstrated the highest infraspinatus/posterior deltoid activity ratio (p < 0.001). Conclusions: The MABER position can be used as an effective exercise to strengthen the infraspinatus muscle. This study contributes to the literature by comparing MABER with traditional exercises and highlights its potential benefits for individuals with rounded shoulder posture.