Mediating the Connection: The Role of Pain in the Relationship between Shoulder Muscle Strength, Joint Position Sense, and Sub-Acromial Impingement Syndrome

Sub-acromial Impingement Syndrome (SIS) is a prevalent shoulder pathology characterized by pain, muscle weakness, and altered joint position sense (JPS). This prospective study aimed to comprehensively assess the relationship between shoulder muscle strength, JPS, and pain in individuals with SIS. A total of 100 participants, including 50 with SIS and 50 healthy controls, underwent shoulder muscle strength testing and JPS evaluation in various directions (flexion, abduction, medial rotation, and lateral rotation). Pain intensity was quantified using a visual analog scale. Correlation analyses were conducted to explore the associations between muscle strength, JPS, and pain, with Cohen's d values indicating the effect size. Individuals with SIS exhibited significantly lower shoulder muscle strength and greater JPS errors compared to the healthy controls (p < 0.001, Cohen's d = 0.51 to 0.84). The results showed strong positive correlations between muscle strength and JPS in all assessed directions (p < 0.001, with r values ranging from 0.35 to 0.62). Mediation analysis revealed that pain partially mediated the relationship between muscle strength and JPS in all directions (p < 0.005). This study highlights the multifaceted nature of SIS, emphasizing the coexistence of muscle weakness, proprioceptive impairments, and pain. The findings underscore the importance of addressing these factors in the comprehensive rehabilitation of individuals with SIS to optimize functional outcomes and enhance their quality of life.