There are no official guidelines to assist in answering this question. I will search for relevant research papers instead.
From the Research
Muscles Associated with Scapular Pain
The muscles associated with scapular pain include:
- Upper, middle, and lower trapezius 1
- Rhomboid major and minor 1
- Serratus anterior 1, 2, 3
- Levator scapulae 1, 2, 4
- Pectoralis minor 1, 4
Muscle Dysfunction and Scapular Pain
Muscle dysfunction, such as:
- Overactivity of the pectoralis minor 1
- Underactivity or paralysis of the serratus anterior or trapezius muscles 1
- Dyskinesis resulting from compensatory mechanisms in patients with recurrent glenohumeral instability due to Ehlers-Danlos syndrome 1 can lead to scapular pain and abnormal scapular motion.
Scapular Muscle Stiffness and Pain
Studies have shown that scapular muscle stiffness, particularly in the middle and lower trapezius, is associated with chronic shoulder pain 2. Additionally, increased stiffness in the middle trapezius has been observed in individuals with pain in the non-dominant side 2.
Scapular Stabilization Exercises and Pain Relief
Scapular stabilization exercises have been shown to improve treatment effectiveness on shoulder pain, scapular dyskinesis, muscle strength, and function in patients with subacromial pain syndrome 5. These exercises can help alleviate scapular pain and improve overall shoulder function.