Fung J, Macpherson J M
R.S. Dow Neurological Sciences Institute, Portland, Oregon 97209.
J Neurosci. 1995 Feb;15(2):1121-31. doi: 10.1523/JNEUROSCI.15-02-01121.1995.
The purpose of this study was to investigate the determinants of postural orientation by examining stance kinematics and kinetics at various interpaw distances. Four adult cats were trained to stand, unrestrained, on a force platform. Three-dimensional ground reaction forces and kinematics, as well as EMG activities, were recorded during stance at five different anteroposterior (AP) distances and two widths. Stance distance was varied by changing the distance between the four force plates mounted on the platform. All cats used a strategy of maintaining a constant horizontal orientation of the trunk and levering the limbs at the girdles while maintaining constant intralimb geometry to accommodate the changes in stance distance. The direction of the ground reaction forces covaried with the limb axes. As a result, the joint torques were conserved in the forelimb, and varied within small ranges in the hind. Increased tonic activity in the extensors of the back, the hip, and the ankle was observed at shorter distances while increased knee extensor activity was observed at longer distances. A cost function, defined as the sum of squared 3-D joint torques, was minimal for the hindlimb at a stance distance which corresponded to the preferred distance naturally assumed by each cat on the floor. Thus, in the maintenance of stance posture, trunk orientation and intralimb geometry is constrained, the goal of which is to minimize muscular effort or energy expenditure.
本研究的目的是通过检查不同爪间距离下的站立运动学和动力学来探究姿势定向的决定因素。训练四只成年猫在无束缚的情况下站在测力平台上。在站立过程中，记录五个不同前后（AP）距离和两个宽度下的三维地面反作用力、运动学以及肌电图活动。通过改变安装在平台上的四个测力板之间的距离来改变站立距离。所有的猫都采用了一种策略，即在保持肢体内部几何形状不变以适应站立距离变化的同时，保持躯干水平方向不变，并在关节处撬动四肢。地面反作用力的方向与肢体轴线相关。结果，前肢的关节扭矩保持不变，而后肢的关节扭矩在小范围内变化。在较短距离时，观察到背部、髋部和踝关节伸肌的紧张性活动增加，而在较长距离时，观察到膝关节伸肌活动增加。一个定义为三维关节扭矩平方和的代价函数，在后肢处于与每只猫在地面上自然采用的偏好距离相对应的站立距离时最小。因此，在维持站立姿势时，躯干定向和肢体内部几何形状受到限制，其目的是使肌肉努力或能量消耗最小化。
