Physiology-based model of the pendulum test

We simulated the dynamics of a pendulum test based on a torque-driven biomechanical model of the lower leg. Our model consisted of a planar lower leg segment with passive stiffness and damping to simulate non-contractile musculotendon properties. Active joint torques representing muscle contractile behavior consisted of a constant baseline torque to represent increased muscle tone, a short-range stiffness torque dependent on the level of muscle tone, and a delayed sensory feedback torque to simulate reflex activity. Muscle short-range stiffness was scaled as a function of muscle tone. We simulated the reflex contributions to the pendulum test by modeling sensory feedback pathways based on either joint position and velocity to represent muscle length and velocity, or active torque and derivative of active torque to represent muscle fiber force and derivative of force. All model parameter values were held constant over the time course of each simulation. To simulate different degrees of spasticity, we altered both muscle tone and the sensitivity of the simulated reflex pathways, i.e. feedback gain values. Our evaluations of the model were based on published kinematic trajectories of the pendulum test in individuals with CP. We were able to reproduce all three key features of the pendulum test associated with increased spasticity: 1) reduced amplitude of the first swing excursion, 2) reduced number of oscillations, and 3) less vertical resting angle. The simulations are freely available (simtk.org) such that other researchers can reproduce our results and perform additional analyses. <br/><br/>This project includes the following software/data packages: <br/> <ul> <li> <a href="https://simtk.org/frs?group_id=1581#pack_2040">pendulumtest_v1.0 </a> : This package provides Matlab code for simulating the pendulum test in spasticity. </li> </ul>

本研究基于驱动力矩的生物力学模型对小腿的摆动测试动力学进行了模拟。本模型由一个具有被动刚度和阻尼的二维小腿段组成，以模拟非收缩性肌腱特性。代表肌肉收缩行为的主动关节扭矩包括表示肌肉张力增加的恒定基线扭矩、依赖于肌肉张力水平的短程刚度扭矩以及模拟反射活动的延迟感觉反馈扭矩。肌肉的短程刚度随肌肉张力而变化。我们通过基于关节位置和速度（以代表肌肉长度和速度）或主动扭矩及其导数（以代表肌纤维力量及其导数）的感觉反馈途径建模来模拟对摆动测试的反射贡献。所有模型参数值在每次模拟的时间过程中保持恒定。为了模拟不同程度的痉挛，我们调整了肌肉张力以及模拟反射途径的敏感性，即反馈增益值。我们的模型评估基于CP患者摆动测试的已发表的运动轨迹。我们能够再现与增加痉挛相关的摆动测试的三个关键特征：1）第一次摆动幅度的减少，2）振荡次数的减少，以及3）垂直静止角度的降低。模拟结果可免费获取（simtk.org），以便其他研究人员能够复制我们的结果并执行额外的分析。本项研究涉及以下软件/数据包：pendulumtest_v1.0：此软件包提供Matlab代码，用于模拟痉挛状态下的摆动测试。