Structure and Function of the Upper Trapezius and Its Role in Chronic Shoulder Pain: an Investigation of Kinematics, Morphology, Muscle Quality and Activation Distribution

Prior research has explored factors influencing muscle activation, including muscle thickness, fear avoidance beliefs (kinesiophobia), and somatosensory integration. In individuals with chronic shoulder pain, various characteristics impacting symptoms and treatment outcomes have been identified, such as psychosocial factors, fear avoidance, central sensitization, somatosensory impairments, and brain morphology changes. These shared characteristics affecting both muscle activation and chronic shoulder pain may potentially modulate upper trapezius muscle activation during functional movements in patients with chronic shoulder pain. Notably, there remains a gap in the literature concerning investigations into the upper trapezius muscle's morphology and quality, fear avoidance, central sensitization, somatosensory impairments, and their interplay with upper trapezius muscle activation in chronic shoulder pain patients. To address these gaps, this study aims to: this study aims to: 1) compare different methods of measuring clavicular kinematics using an electromagnetic tracking system; 2) establish the reliability and validity of measuring muscle thickness and fat infiltration through ultrasound and magnetic resonance imaging; 3) compare shoulder kinematics, muscle activation, muscle morphology, and muscle fat infiltration in individuals with chronic shoulder pain with matched healthy controls; 4) explore the correlation between the factors that may influence upper trapezius muscle activation, including basic data of the subjects, muscle morphology, and muscle fat infiltration.