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.

Inclusion Criteria:

• Chronic shoulder pain group

  • 18-50 years old18-50 years old
  • unilateral and non-traumatic shoulder pain
  • pain duration longer than 3 months
  • pain intensity more than VAS=2 during movement
  • presence 3 of 5 positive pain provocation tests: Hawkins-Kennedy test, Jobe test, or Neer's test Painful Arc, and Resistance Test against External Rotation.

• Healthy control group

  • presenting no shoulder pain at rest or during daily activities
  • negative results of the pain provocation test: Hawkins-Kennedy test, Jobe test, Neer's test, Painful Arc, Resistance Test against External Rotation and Spurling's neck compression test.

Exclusion Criteria:

- Chronic shoulder pain group

• history of significant shoulder trauma, such as fracture or ultrasonography clinically suspected full thickness cuff tear
• recent shoulder dislocation in the last 2 years
• diagnosis of adhesive capsulitis characterized by a gradual and painful loss of both active and passive ROM in all shoulder planes, primarily external rotation
• shoulder pain originating from the cervical spine by using Spurling's neck compression test
• shoulder pain owing to the following disorders: arthritis (e.g., rheumatoid arthritis, osteoarthritis of shoulder complex), neurologic (e.g., stroke), neoplastic (e.g., breast cancer). and/or referred pain (e.g., visceral referred pain)
• corticoid injections over the shoulder during 6 months prior to the study
• history of shoulder and neck surgery

Community Sample