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[PURPOSE] The aim of this study was to suggested the best way of Squat by estimating and analyzing muscle activity in waist and lower limbs, the number of set repeat-count, and total momentum when we change the width of stance and the angle of knee joint in Squat. [METHODS] In this study, we recruited 10 subjects from the college of physical education, who had built a career at resistance exercise over 1 years. They were divided into five groups by way of Squat. The exercise was executed with 75% 1RM and estimated by randomized-crossover way. The speed of exercise was not limited, and in each set we counted the number of set repeat-count by estimating maximum repetition of each group. we estimated total momentum by multiplying maximum repetition and weight. We estimated an EMG at rectus femoris, vastus medialis, vastus lateralis, erector spinae, and calculate the result by iEMG. After analyzing by two-way ANOVA, We have some significant result from the study. [RESULTS] There was no difference in the number of repetitions and the total work during Squat according to stance width. The rectus femoris and erector spinae showed high iEMG in narrow stance squat and wide stance squat. The vastus lateralis showed high iEMG in narrow stance squat. The vastus medialis showed high iEMG in wide stance squat. The number of repetitions and total momentum in the squat exercise according to the knee angle were 45° harf squat, 90° standard squat, and 120° deep squat. The iEMG responses of quadriceps femoris and erector spinae were 90° standard squat and 120° deep squat higher than 45° harf squat. [CONCLUSION] The smaller the stance width at the squat, the higher the muscle activity of rectus femoris and erector spinae. As the knee angle increased during the squat, the number of repetitions decreased and the muscle activity of quadriceps femoris and erector spinae was higher. This requires attention to knee and back injuries when squatting with a narrow stance and a deep knee angle. In addition, there is a need to perform different exercise loads according to the knee angle during the squat exercise.