Human postural control requires continuous modulation of ankle torque to stabilize the upright stance. The torque is generated by two components: active contributions, due to central control and stretch reflex, and passive mechanisms, due to joint intrinsic stiffness. Identifying the contribution of each component is difficult, since their effects appear together, and standing is controlled in closed-loop. This article presents a novel multiple-input, single-output method to identify central and stretch reflex contributions to human postural control. The model uses ankle muscle EMGs as inputs and requires no kinematic data. Application of the method to data from nine subjects during standing while subjected to perturbations of ankle position demonstrated that active torque accounted for 84.0± 5.5% of the ankle torque. The ankle plantar-flexors collectively produced the largest portion of the active torque through central control, with large inter-subject variability in the relative contributions of the individual muscles. In addition, reflex contribution of the plantar-flexors was substantial in half of the subjects, showing its potentially important functional role; finally, intrinsic contributions, estimated as the residual of the model, contributed to 15% of the torque. This study introduces a new method to quantify the contributions of the central and stretch reflex pathways to postural control; the method also provides an estimate of noisy intrinsic torque with significantly increased signal to noise ratio, suitable for identification of intrinsic stiffness in standing. The method can be used in different experimental conditions and requires minimal a-priori assumption regarding the role of different pathways in postural control.

中文翻译：

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确定中央和伸展反射对人体姿势控制的贡献

人体姿势控制需要连续调节脚踝扭矩以稳定直立姿势。扭矩由两个部分生成：由于中央控制和拉伸反射而产生的主动贡献，以及由于关节固有刚度而产生的被动机制。很难确定每个组件的作用，因为它们的作用会同时出现，并且站立状态是闭环控制的。本文提出了一种新颖的多输入单输出方法，以识别中枢反射和拉伸反射对人体姿势控制的贡献。该模型使用脚踝肌肉肌电图作为输入，不需要运动学数据。该方法对九个受试者站立时受到脚踝位置扰动的数据的应用表明，主动扭矩占脚踝扭矩的84.0±5.5％。脚踝-屈肌通过中央控制共同产生最大的主动扭矩，个体间相对肌肉的个体间差异较大。此外，在一半的受试者中，足底屈肌的反射贡献很大，显示出其潜在的重要功能作用。最后，作为模型残差的内在贡献贡献了15％的扭矩。这项研究引入了一种新的方法来量化中枢和伸展反射通路对姿势控制的贡献。该方法还提供了带有明显增加的信噪比的噪声固有转矩的估计值，适用于识别站立时的固有刚度。