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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 (P<.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.
Ekstrom et al. (Sat,) studied this question.