The purpose of this study was to compare the muscle activities of Double Legged Jump (DLJ) and Single Legged Jump (SLJ) by the normalization of muscle activity. Eight college students without the lower extremity injuries were selected as subjects for collecting EMG data of vastus medialis and gastrocnemius. The entire section of motion was established as eccentric and concentric contractions, and each of the contractions was divided into three sections with equal timing intervals, which becomes a total of 6 phases. The EMG data of each phase was integrated and normalized. The muscle activities of the vastus medialis for both eccentric and concentric contractions were significantly different between DLJ and SLJ(p<.05). The increase in overall muscle activity of SLJ was 33.6%. Approximately, there was an increase of 25.9% in eccentric contraction and 40% in concentric contraction. Moreover, the data of the muscle activity of gastrocnemius was similar to the data of the muscle activity of vastus medialis. In conclusion, this research suggests muscle activity of a certain motion can be normalized for an analysis of another motion.