Selective Activation of the Subscapularis Muscle: A Cross-Sectional Observational Study

Background/Objectives: Clinicians have employed various therapeutic exercises to enhance the function and strength of the subscapularis muscle (SSC). However, few studies have investigated the most effective exercise for selectively activating the SSC while minimizing compensation from surrounding shoulder musculatures. Methods: Forty healthy participants without any shoulder complex conditions participated in this study. Individuals with a history of shoulder pain or musculoskeletal or neurological conditions affecting shoulder internal rotation were excluded. Participants performed three exercises: (1) Belly Press, (2) Lift Off, and (3) Prone Wiper, in a randomized order generated using Microsoft Excel. Ultrasound was then performed to assess the SSC and infraspinatus (IS) muscle thickness. Surface electromyography was used to record anterior deltoid (AD), pectoralis major (PM), and posterior deltoid (PD) muscle activity. Radiographic imaging was employed to evaluate the path of the instantaneous center of rotation (PICR). Data were analyzed using a one-way repeated-measures analysis of variance (ANOVA), followed by Bonferroni adjustment. Results: A significant reduction in IS thickness and PICR was observed only following the Belly Press (p < 0.05). Electromyographic activity of AD, PM, and PD increased significantly across all exercises (p < 0.05). These results demonstrate that the Belly Press most effectively allows the SSC to generate force while maintaining a stable center of rotation during shoulder movement. Conclusions: The Belly Press was most effective in selectively activating the SSC while minimizing surrounding shoulder rotator muscle activity and reducing PICR. This finding may help clinicians identify and treat patients with shoulder internal rotation injuries.