Purpose of the Study This study looks at whether using real-time ultrasound images as feedback can help people better activate two important shoulder muscles-the serratus anterior and lower trapezius-compared to standard verbal or visual feedback from a clinician. The study also examines whether this training carries over to everyday arm movements and whether it helps create more space inside the shoulder joint.

Why This Matters Shoulder pain is very common. One possible cause is poor movement or poor muscle control of the shoulder blade, which can reduce the space under the shoulder and lead to pain. The serratus anterior and lower trapezius muscles help the shoulder blade move correctly when lifting the arm. Improving how these muscles work may reduce pain and improve shoulder function.

How the Study Is Done

People with shoulder pain will take part in the study in a university laboratory. They will be randomly placed into one of two groups:

One group will receive muscle training with ultrasound images that show their muscles working in real time.

The other group will receive standard feedback without ultrasound.

Participants will perform specific shoulder exercises targeting the two muscles. Muscle activity will be measured before and after training using specialized sensors. The researchers will also see if the muscle training improves muscle use during a more functional movement, such as lifting the arm to shoulder height. In addition, ultrasound will be used to measure the space inside the shoulder joint before and after training.

Why This Is Important for Care If ultrasound feedback is shown to be effective, it could give physical therapists and other clinicians a new tool to help patients better activate key shoulder muscles. This may improve treatment options for people with shoulder pain, especially pain at the top of the shoulder.

Introduction

Shoulder pain is very common and affects people all over the world. About 1 in 6 people experience shoulder pain at any given time, and many new cases occur each year. It is one of the top causes of muscle and joint pain, behind only a few other conditions. Shoulder pain can significantly affect daily activities and quality of life, with common diagnoses including rotator cuff problems and shoulder impingement.

Pain at the top of the shoulder often happens when people lift their arms overhead. For the shoulder to move properly, the shoulder blade must move in a coordinated way with the arm. When the arm lifts, the shoulder blade needs to rotate upward, tilt backward, and rotate slightly outward. These movements depend heavily on certain muscles, especially the serratus anterior and the upper and lower trapezius muscles.

Research has shown that people with shoulder pain often have poor muscle balance around the shoulder blade. In many cases, the upper trapezius muscle becomes overactive, while the lower trapezius and serratus anterior muscles are underactive. This imbalance can interfere with normal shoulder movement and may contribute to pain.

Another factor linked to shoulder pain is a decrease in the space inside the shoulder joint where tendons pass. When this space becomes smaller, structures in the shoulder can become pinched during arm movements, especially overhead. Proper movement of the shoulder blade helps lift part of the shoulder bone out of the way, preventing this pinching. Studies show that strengthening and retraining shoulder blade muscles can reduce pain and improve shoulder function. Other research has demonstrated that activating the serratus anterior and lower trapezius muscles can actually increase the space inside the shoulder joint, highlighting the importance of proper muscle control.

Physical therapists use many techniques to help patients activate muscles correctly, including verbal cues, hands-on guidance, and visual feedback. One newer method is real-time ultrasound imaging, which allows people to see their muscles contract on a screen while exercising. This approach has been shown to improve activation of several muscles, including the serratus anterior. However, past studies have not examined whether ultrasound feedback improves muscle activation during everyday arm movements, increases shoulder joint space, or affects the lower trapezius muscle.

The goal of this study is to compare ultrasound-based feedback with standard feedback to see which method better improves activation of key shoulder muscles during functional movements. A secondary goal is to determine whether this training increases the space inside the shoulder joint during arm lifting.

Materials and Methods Participants

Twenty-six adults with shoulder pain will take part in this study. Participants will be recruited through flyers, word of mouth, and social media. To be included, individuals must be able to lift their arm above shoulder height and report at least mild shoulder pain. People will be excluded if they have severe pain, nerve disorders, neck-related shoulder pain, a history of shoulder surgery or fractures, frozen shoulder, or if they have already received specialized training for shoulder blade muscles.

Each participant will complete questionnaires about their pain, shoulder function, and personal background. They will then be randomly placed into one of two groups: one group will receive ultrasound feedback during training, and the other will receive standard feedback. All participants will provide written consent, and the study has been approved by a university ethics board.

Muscle Activity Measurement

Small sensors will be placed into the serratus anterior and lower trapezius muscles to measure how active these muscles are during different movements. This method allows researchers to measure muscle activity very accurately while minimizing interference from nearby muscles. Ultrasound imaging will be used to guide sensor placement to ensure accuracy.

Measuring Shoulder Joint Space

Before and after the training session, ultrasound imaging will be used to measure the space inside the shoulder joint while participants hold their arm at different angles. Participants will sit upright and gently push against a strap to keep consistent effort. Several images will be taken at each arm position to ensure accurate measurements.

Functional and Muscle-Specific Tasks

Muscle activity will be recorded while participants perform:

A functional arm movement that mimics everyday shoulder use

A targeted exercise for the serratus anterior

A targeted exercise for the lower trapezius

Each movement will be repeated several times, and arm movement speed and height will be carefully controlled to keep testing consistent.

Intervention Standard Feedback

Participants receiving standard feedback will be guided using verbal instructions and hands-on cues from the examiner to help them activate the correct muscles during exercises.

Ultrasound Feedback

Participants in the ultrasound group will watch their muscles contract on a screen while performing the same exercises. The examiner will explain what the muscle should look like on the screen and provide cues to help participants increase muscle activation.

Maximum Muscle Effort Testing

At the end of testing, participants will perform short maximal muscle contractions so researchers can compare muscle activity levels across individuals in a standardized way.

Data Analysis

Muscle activity signals will be processed using specialized software to determine average muscle activation levels during each task. The main outcomes will be:

How active the serratus anterior and lower trapezius muscles are

How much space is present inside the shoulder joint

Statistical tests will be used to compare results between groups and before versus after training.

Why This Study Matters

This study may help determine whether ultrasound feedback is more effective than standard instruction for improving shoulder muscle function. The results could give clinicians another tool to better treat shoulder pain and improve movement, especially for people who struggle to activate key shoulder muscles.

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Inclusion Criteria:

• Subjects with apical shoulder pain
• Pain level >2 on the numeric pain rating scale
• Able to elevate shoulder beyond 140º
• Able to perform all research activities without difficulty

Exclusion Criteria:

• Experience shoulder pain > 6 on the numeric pain rating scale
• Presence of a known neurological disorder
• Shoulder pain only elicited with neck movements
• History of shoulder fracture or surgery involving the glenohumeral joint capsule
• Diagnosis of adhesive capsulitis
• Previously received treatment for the scapular upward rotators

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