Altered Gluteus Maximus and Latissimus Dorsi Activation in Subacromial Impingement Syndrome: Implications for Kinetic Chain Dysfunction

Background/Objectives: Subacromial impingement syndrome (SIS) may be associated with altered kinetic-chain mechanics above and below the shoulder. The posterior oblique sling integrates the gluteus maximus and latissimus dorsi through established fascial and neuromuscular connections, yet empirical evidence examining its relevance in SIS remains limited. Therefore, this cross-sectional observational study aimed to investigate the surface electromyographic (sEMG) activity of the latissimus dorsi (LD) and contralateral gluteus maximus (GM) and evaluate their associations with pain, disability, and shoulder range of motion (ROM) in young adults with SIS. Methods: Sixty sedentary young adults with SIS and matched controls were assessed using the Numeric Pain Rating Scale, Arabic QuickDASH, twin-axis electrogoniometer, and sEMG of the gluteus maximus and latissimus dorsi. Results: The SIS group had significantly lower GM activity (23.96 ± 3.54% MVIC for SIS and 34.49 ± 4.16% MVIC for controls) and significantly higher LD activity (118.63 ± 24.87% MVIC for SIS and 75.52 ± 25.93% MVIC for controls) (p = 0.001). In addition to these differences, the SIS group exhibited significantly less ROM in all directions (flexion, extension, abduction, and rotation) and greater disability and pain intensity (both p = 0.001) than controls. Correlations between sEMG activity and clinical outcome measures in the SIS group were weak and not statistically significant. Discriminant logistic regression indicated that both GM and LD sEMG were significant discriminative variables of group membership, with GM underactivity showing the greater discriminative value. Conclusions: These results indicate an altered neuromuscular activation pattern observed in participants with SIS, characterized by decreased GM and increased LD sEMG activity. They may justify further investigation of kinetic-chain-informed rehabilitation, with attention to both hip/lumbopelvic function and shoulder-based treatment.