Effect of the Shoulder Flexion Angle in the Sagittal Plane on the Muscle Activities of the Upper Extremities when Performing Push-up plus Exercises on an Unstable Surface

[Purpose] The purpose of this study was to investigate the effect of the shoulder flexion angle on the muscle activities of the upper extremities when performing the push-up plus exercise (PUPE) on an unstable surface with the forearm in the external rotation position. [Subjects] The subjects were conducted on 15 normal male adults. [Methods] A sling device was used for the unstable surface, and PUPE was performed with the forearm in the external rotation position. The shoulder flexion angles measured in the sagittal plane were 110°, 90°, and 70°. Electromyography was used for a comparitive analysis of the muscle activities of the serratus anterior (SA), the pectoralis major (PM), and the upper trapezius (UT). [Results] In the intra-group comparison, the muscle activity of SA was statistically the highest when the shoulder-flexion angle was 110°. [Conclusion] performing PUPE on an unstable surface, the muscle activity of the SA is activated the most when the shoulder flexion angle is 110° and the forearm is in the external rotation position.