The purpose of this study was to compare the shoulder stabilizer muscle activity during a push up plus on a different conditioning surface. Eighteen healthy volunteers were tested. Surface EMG was recorded from the upper trapezius(UT), pectoralis major(PM), and serratus anterior(SA) using surface differential conditions. Measurements were performed for 7 days. The mean root mean square (RMS) of EMG activity was calculated. A one-way repeated measures analysis of variance was performed to compare RMS normalized values. The UT and PM did not show significant differences of electric activation amplitude in relation to different surface conditions(p>.05). However, the SA showed greater mean electric activation amplitude values on the push up plus exercise on a upper and lower unstable surface(p<.05). These results suggest that to improve SA EMG activity is more useful when performed on a upper and lower unstable surface conditions than on a stable surface conditions.