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Day J.1, Dale R.1
1University of South Alabama, Physical Therapy, Mobile, United States
Background: Research consistently demonstrates that individuals with shoulder pathologies are likely to have altered serratus anterior (SA) muscle performance. Assessment of the SA using ultrasound imaging (UI) allows real time visualization of the isolated changes in muscle thickness. A reliable method for measuring SA thickness has been reported, yet the procedure has never been formally validated.
Purpose: The purpose of this study was to determine the relationship between electromyography (EMG) and percent change in thickness of the SA as measured by UI.
Methods: Thirty healthy subjects (mean age 24 SD±2, 53% male, 94% right handed) were positioned in a standardized sitting posture and anatomical landmarks were marked for ultrasound probe and EMG surface electrode placement. Tegaderm occlusive dressing was applied over the electrode in order to prevent ultrasound gel from interfering with the EMG signal. EMG activity of the SA was recorded during rest, and subsequent isotonic EMG activity was normalized to the subjects maximum voluntary isometric contraction (MVIC). Subjects were asked to raise the upper extremity from a resting position to 120º of scaption for a total of three trials. Upper extremity elevation velocity was externally paced by previously recorded verbal instructions at a rate of 10º per second. EMG activity was collected through the entire range of motion, while ultrasound images were taken at rest and at 120º of scaption. EMG signals were real-time conditioned with proprietary manufacturer software (Sierra Wave). SA thickness measures were obtained post hoc with manufacturer software (Mindray MSK Z6). Percent change in thickness was calculated by subtracting the average rest value from the average contractile value, and dividing the difference by the average rest value. A paired t-test was used to compare absolute resting from contractile values at 120º of scaption both for EMG and ultrasound data. Pearsons correlation coefficient was used to determine the relationship between the normalized EMG activity at 120º of elevation and the ultrasound data.
Results: There were significant increases in both EMG activity and absolute muscle thickness when comparing resting values to 120º of scaption (p .001). There was a significant relationship between percent MVIC EMG activity and the percent change in muscle thickness (p=.01) (r =.49, r2= .26).
Conclusion(s): There is a moderate positive relationship between Percent MVIC SA EMG activity and percent change in muscle thickness as measured by UI. However, more research is needed with a pathological population to validate the use of UI in measuring SA muscle performance.
Implications: UI has the potential to be used on the SA as a means of assessment or biofeedback in a clinical setting.
Funding acknowledgements: Not applicable
Topic: Musculoskeletal: upper limb
Ethics approval: The study protocol was approved by the University of South Alabamas Institutional Review Board. Subjects rights were protected.
All authors, affiliations and abstracts have been published as submitted.
