Purpose : The purpose of this study was to compare the muscle activities of infraspinatus, serratus anterior, upper trapezius, and triceps brachii in different supporting surface intervals during push-up exercise. Method : Subjects of the study were 18 healthy male students without any orthopedic or neurological injuries including neck and shoulder surgeries and can perform a push-up exercise required for the study. EMG was used to measure the muscle activities of four muscles. Result : There were statistically significant differences of all the muscles in three different supporting surface intervals(p<0.5). Muscle activity of upper trapezius was the highest(MVIC 39.40%) in the narrowest width and the lowest in the widest width. In infraspinatus, muscle activity was the highest(MVIC 36.23%) in the narrowest width and the lowest in the widest width. In serratus, muscle activity is the highest(MVIC 58.04%) in the widest width and the lowest in the narrowest width. In triceps brachii, muscle activity is the highest(MVIC 68.51%) in the widest width and the lowest in the narrowest width. Conclusion : Muscle activities are at the highest with the narrowest width in the upper trapezius and the infraspinatus. In the serratus and triceps brachii, however, muscle activities are at the highest with widest width.