In this paper we investigate the relation between the position of center of gravity on postural stability and the balance of muscular strength of the lower limbs. The index of the balance were Leg extension, which was the front, and Leg curl was the back. One Repetition Maximum of muscular strength was calculated using by repetition maximum method. The center of gravity on postural stability was measured using FPS (Foot Pressure System). The result were as follows, To train both of the extension and the curl, it was a primary factor that changing more better balance and position, but it must to use properly two cases. 1) Shifting the position of center of gravity toward the front, in this case, it should be training the extention first, and next time, it should be training the curl. 2) Shifting the position of center of gravity toward the back, in this case, it should be training the curl. These methods were necessary to cure a posture.