An Electromyographic Study of Upper Trapezius, Lower Trapezius, and Serratus Anterior Muscle Activity during Traditional and Modified Muscle Testing Positions
Date of Award
Doctor of Physical Therapy (DPT)
Electromyography; Muscle, Skeletal -- physiology; Shoulder -- physiology
Purpose: The purpose of this study is to assess the muscle activity of the shoulder joint force couple induced by the upper trapezius, lower trapezius, and serratus anterior to determine if they are more effectively recruited during the traditional exercise position of forward shoulder elevation in 145° of shoulder abduction versus a modified position of shoulder external rotation while in 80° of shoulder abduction and 90° of elbow flexion
Methods: Nine participants took part in this randomized study in which EMG data was collected during 4 exercise trials of 10 repetitions each on the right shoulder. EMG activity was monitored in the upper trapezius, lower trapezius, upper serratus anterior, and lower serratus anterior in the standard manual muscle testing position for the lower trapezius and a modified position with and without a two pound hand weight. The modified position had the shoulder in 80° of shoulder abduction with the elbow flexed to 90°, and palm facing the floor.
Results: All subjects were able to complete the study except one who was excluded due to data corruption. Not surprisingly, more EMG activity was found in the four muscles for positions using weight compared to the no weight position regardless of the testing position implemented. The EMG activity, in the modified position, is decreased in the upper trapezius and lower serratus when compared to the standard position. This is true regardless of the presence of the two pound weight. In the lower trapezius and the upper serratus there is no significant difference between the modified and standard positions regardless of the presence of the two pound weight.
Conclusion: The modified position recruits similar motor units in the lower trapezius and upper serratus. There is a significant reduction in EMG activity in the upper trapezius and lower serratus when comparing modified and standard testing positions.
Everett, Jace; Fowler, Mike; Haak, Jason; and Luck, Robby, "An Electromyographic Study of Upper Trapezius, Lower Trapezius, and Serratus Anterior Muscle Activity during Traditional and Modified Muscle Testing Positions" (2006). Physical Therapy Scholarly Projects. 131.