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Study Design: This study used a prospective, single-group repeated-measures design to analyze differences between the electromyographic (EMG) amplitudes produced by exercises for the trapezius and serratus anterior muscles. Objective: To identify high-intensity exercises that elicit the greatest level of EMG activity in the trapezius and serratus anterior muscles. Background: The trapezius and serratus anterior muscles are considered to be the only upward rotators of the scapula and are important for normal shoulder function. Electromyographic studies have been performed for these muscles during active and low-intensity exercises, but they have not been analyzed during high intensity exercises. Methods and Measures:Surface electrodes recorded EMG activity of the upper, middle, and lower trapezius and serratus anterior muscles during 10 exercises in 30 healthy subjects. Results: The unilateral shoulder shrug exercise was found to produce the greatest EMG activity in the upper trapezius. For the middle trapezius, the greatest EMG amplitudes were generated with 2 exercises: shoulder horizontal extension with external rotation and the overhead arm raise in line with the lower trapezius muscle in the prone position. The arm raise overhead exercise in the prone position produced the maximum EMG activity in the lower trapezius. The serratus anterior was activated maximally with exercises requiring a great amount of upward rotation of the scapula. The exercises were shoulder abduction in the plane of the scapula above 120°and a diagonal exercise with a combination of shoulder flexion, horizontal flexion, and external rotation. Conclusion: This study identified exercises that maximally activate the trapezius and serratus anterior muscles. This information may be helpful for clinicians in developing exercise programs for these muscles.

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Study Design: Prospective single-group repeated-measures design. Objective: To use electromyographic (EMG) analysis during muscle testing to determine if there is a difference in function of the upper and lower parts of the serratus anterior (SA) muscle. Background: The SA muscle is a very important scapular protractor and upward rotator. Authors have anatomically described the muscle as being divided into 2 or 3 parts, and have suggested that the upper part is more suited for protraction and the lower part for upward rotation of the scapula. Methods and Measures:Surface electrodes recorded EMG activity of the upper and lower parts of the SA muscle during 9 different muscle tests in 29 healthy subjects. Results: Three muscle tests demonstrated significantly greater (PϽ.05) EMG activity in the lower part of the SA as compared to the upper part. There was no significant difference in the EMG activity of the upper and lower parts of the SA when the other 6 muscle tests were analyzed. Conclusion: When upward rotation was the primary position of the scapula during the muscle tests, the lower part of the SA was activated to a greater degree than the upper part. Muscle tests with maximum scapular protraction with varying degrees of upward rotation produced EMG activity with no significant difference when comparing the upper and lower parts of the SA. This information may be helpful for clinicians when muscle testing and developing exercise programs for the SA muscle.