Purpose This study was performed to determine the activity of the serratus anterior (SA), the upper trapezius (UT) and the lower trapezius (LT) muscles along the angles(20°, 0°, －20°) and scales(50%, 65%, 80% of 1RM) of resistance during scapular protraction. Methods Thirtythree health subjects with no medical history of spine, upper extremity and hand disorders were recruited for this study. Subjects performed scapular protraction at 20°, 0°, －20° angles of resistance with 50%, 65%, and 80% of 1RM scales of resistance in standing position. Muscular activation were measured by surface electromyography (EMG). A 3 (angles) × 3 (scales) twoway analysis of variance (ANOVA) was used to compare the normalize activities of the serratus anterior, the upper trapezius and the lower trapezius muscles. Results Only in the lower trapezius muscle became different significantly according to angles (p <.05) during the scapular protraction. The serratus anterior, the upper trapezius and the lower trapezius muscles became different significantly according to scales (p<.05). The shoulder muscles between angles and scales did not show significant difference during the scapular protraction

(p >.05). Conclusion Based on the results of this study, using the shoulder muscles activity according to the angles and scales of resistance, by apply an optional exercise for each shoulder muscles may be used to for patients with the shoulder impingement syndrome by the insufficient scapular protraction and upward rotation by shoulder muscles imbalance.