Experimental results are described to clear the function of bouncing-type prosthetic knee joints during the stance phase. The moments and forces acting on the hip, knee and ankle joints of prosthetic side in the level walking of three active young amputees were measured by instrumented pylon installed in the shank part and flexible electro-goniometer attached on the hip, knee and ankle joints. From these data, the bouncing knee joints showed the following characteristics 1) The hip joint angular displacement of prosthetic side in the early stance phase was very close to that of normal subject. This shows that the vertical displacement of the gravity center decreased compared with other knee joints. 2) The inclination of the first peak of the compressive force acting on the shank was smaller than other knee joints, and this showed more absorption of the impact force at heel contact compared with other knee joints. 3) The period of the dorsi-flexion of ankle joint is shorter than other knee joints. This shows that foot-flat occurs earlier and increases the stability of stance phase period compared with other knee joints. 4) The positive power of the knee joint in the stance phase was very smaller than that of normal subject and had poor effect on the push-off motion.
