Institute of Mechanical Engineering (IDMEC), Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal.
Institut de Biomécanique Humaine Georges Charpak Arts et Métiers ParisTech, Paris, France.
J Biomech. 2022 Jan;130:110829. doi: 10.1016/j.jbiomech.2021.110829. Epub 2021 Oct 30.
Multivariable ankle mechanical impedance was estimated in four stroke survivors, in coupled dorsi- plantarflexion and inversion-eversion. We applied external torque perturbation with an ankle robot and used multi-input, multi-output stochastic system identification methods to estimate impedance, in both paretic and nonparetic limbs. Subjects were instructed to remain at rest throughout the four trials performed on each leg. Impedance projected onto the directions of maximum and minimum stiffness was fit to a 2nd order linear model, including inertia, viscosity and stiffness. For most trials, stiffness and damping in dorsi-plantarflexion are increased on the paretic side. However, for two subjects, overall impedance is not increased in the absence of sustained involuntary tonic contraction, registering values comparable to the non-paretic side. Thus, we speculate that the intrinsic properties of the paretic ankle remained unaffected at the evaluated pose. Spasticity (hyperflexive stretch reflex) would have systematically increased stiffness and damping, even in the absence of involuntary contraction. Hence, we speculate that these two subjects did not exhibit spasticity, while the remaining two subjects did, since impedance was increased, with no involuntary tonic muscle contraction. Regarding inversion-eversion, impedance in this direction remained unaffected by stroke. We evaluated two volunteers before and after the application of botulinum toxin. Surprisingly, ankle stiffness was not reduced, but anisotropy was normalized.
对 4 名脑卒中幸存者在背屈-跖屈和内翻-外翻耦合状态下的多变量踝关节力学阻抗进行了估计。我们使用踝关节机器人施加外部扭矩扰动，并使用多输入、多输出随机系统识别方法来估计阻抗，包括患侧和非患侧肢体。在每条腿上进行的四次试验中，要求受试者始终保持静止。将阻抗投影到最大和最小刚度方向，并拟合到二阶线性模型中，包括惯性、粘性和刚度。对于大多数试验，患侧的背屈-跖屈刚度和阻尼增加。然而，对于两名受试者，在没有持续的不自主紧张收缩的情况下，整体阻抗没有增加，记录的值与非患侧相似。因此，我们推测在评估的姿势下，患侧踝关节的固有特性没有受到影响。痉挛（过度伸展反射）会系统地增加刚度和阻尼，即使在没有不自主收缩的情况下也是如此。因此，我们推测这两名受试者没有表现出痉挛，而其余两名受试者则表现出痉挛，因为在没有不自主紧张性肌肉收缩的情况下，阻抗增加了。关于内翻-外翻，中风对该方向的阻抗没有影响。我们在应用肉毒毒素前后评估了两名志愿者。令人惊讶的是，踝关节刚度没有降低，而是各向异性得到了正常化。
