著者

青木 慶 山崎 信寿

出版者

バイオメカニズム学会

雑誌

バイオメカニズム

巻号頁・発行日

vol.14, pp.59-68, 1998

被引用文献数

4 12

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Joint resistance is the passive torque exerted by viscoelastic tissues such as ligaments, capsules, tendons, and muscles around the joint. The main function of joint resistance is restriction of the range of motion. However its positive role for human bipedal walking has not been clarified. In this study, we developed a three-dimensional passive-walking model that can walk on an inclined plane by utilizing gravitational force and joint resistance. By using the model, we can easily observe the influence of joint resistance on walking. The model consists of eleven rigid segments; head, chest, pelvis, upper arms, forearms, thighs, and shank-foot segments. The foot part is modeled with a semicircular plate and can roll over the slope. The joint resistance is approximated with a nonlinear viscoelastic torque element, which can prevent hyperextension and hypertwist of the joint. In order to prevent the knee joint from flexing at heel contact, minimum active torque exerted by the knee extensor during the first stance phase is measured from real walking and approximated as a nonlinear viscoelastic element. If the passive model is placed on a slope, the supporting leg naturally rotates down on the semicircular foot, and the other leg swings forward until it reaches to the slope surface. This motion is repeated to generate walking. Initial conditions of the segment angles, angular velocity, and walking velocity are determined by an optimization so as to minimize the difference in walking pattern between the first and second steps. For evaluation of the model, we calculated the passive walking with actual and artificially restricted knee properties, and these agreed well with actual walking patterns. We simulated passive walking patterns by measured changes in the knee and hip joint resistances and also the range of joint motion. Body proportions were also changed from those of a baby to those of an adult. These simulated results show the following roles and characteristics of the joint resistance by passive tissues: 1) knee joint resistance is important when active torque is applied and at the end of the stance phase, and hip joint resistance acts during only the last stance phase; 2) the supporting leg behaves like a stick during the first half stance phase; 3) elastic energy is charged up in the hip and knee joint by extension action around the ankle joint; 4) the charged energy is released at the swing phase, and the thigh swings forward and shank swings upward; 5) joint motions are not greatly affected by alternation of joint resistance; 6) the walking cycle lengthens if the resistance is weakened or the joint range becomes wider; 7) the strength of joint resistance relates to the body proportions, namely knee joint resistance relates to shank length, and hip joint resistance relates to the inertial moment of the leg; 8) the active torque around a knee joint has less influence in passive walking; 9) the patterns of joint resistance torque are similar to those of muscular torque in real walking; and 10) joint resistance saves walking energy. Consequently, we can understand that joint resistance is adapted to the body proportions and bipedal walking. This fact is useful in restoring fossil humans and their locomotion.