Selective Activation of the Subscapularis Muscle

Background/Objectives: Clinicians have employed various therapeutic exercises to enhance the function and strength of the subscapularis muscle (SSC). Numerous studies have explored their effectiveness using diverse methodologies. However, the most effective exercise for selectively activating the SSC, while minimizing compensation from surrounding shoulder musculatures, remains unclear. Methods: Forty healthy participants (20 men, 20 women; age = 38.95 ± 3.32 years, height = 166.44 ± 6.72 cm, mass = 65.55 ± 11.38 kg) performed three exercises: (1) Belly Press, (2) Lift Off, and (3) Prone Wiper, 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 only occurred following the Belly Press (p<.05). All other exercises significantly increased SSC and IS thickness relative to baseline (p<.05). Electromyographic activity of AD, PM, and PD increased significantly across all exercises (p<.05), with AD activity differing significantly from the Belly Press and Prone Wiper (p<.05). PICR decreased significantly after the Belly Press (p<.05), but increased significantly following the Lift Off and Prone Wiper (p<.05). Conclusions: The Belly Press was most effective in selectively activating the SSC while minimizing surrounding shoulder rotator muscles activity and reducing PICR. This finding may help clinicians identify and treat patients with shoulder internal rotation injuries.