Department of Mechanical Engineering, Massachusetts Institute of Technology, Room 3-147, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
J Biomech. 2011 Jul 7;44(10):1901-8. doi: 10.1016/j.jbiomech.2011.04.028. Epub 2011 May 14.
Quantitative characterization of ankle mechanical impedance is important to understand how the ankle supports lower-extremity functions during interaction with the environment. This paper reports a novel procedure to characterize static multivariable ankle mechanical impedance. An experimental protocol using a wearable therapeutic robot, Anklebot, enabled reliable measurement of torque and angle data in multiple degrees of freedom simultaneously, a combination of inversion-eversion and dorsiflexion-plantarflexion. The measured multivariable torque-angle relation was represented as a vector field, and approximated using a method based on thin-plate spline smoothing with generalized cross validation. The vector field enabled assessment of several important characteristics of static ankle mechanical impedance, which are not available from prior single degree of freedom studies: the directional variation of ankle mechanical impedance, the extent to which the ankle behaves as a spring, and evidence of uniquely neural contributions. The method was validated by testing a simple physical "mock-up" consisting of passive elements. Experiments with young unimpaired subjects quantified the behavior of the maximally relaxed human ankle, showing that ankle mechanical impedance is spring-like but strongly direction-dependent, being weakest in inversion. Remarkably, the analysis was sufficiently sensitive to detect a subtle but statistically significant deviation from spring-like behavior if subjects were not fully relaxed. This method may provide new insight about the function of the ankle, both unimpaired and after biomechanical or neurological injury.
定量描述踝关节的机械阻抗对于理解踝关节在与环境相互作用时如何支撑下肢功能非常重要。本文报告了一种新的方法来描述静态多变量踝关节机械阻抗。使用可穿戴治疗机器人 Anklebot 的实验方案能够可靠地同时测量多个自由度（内翻-外翻和背屈-跖屈）的扭矩和角度数据。测量的多变量扭矩-角度关系表示为一个向量场，并使用基于薄板样条平滑和广义交叉验证的方法进行近似。该向量场能够评估静态踝关节机械阻抗的几个重要特性，这些特性无法从以前的单自由度研究中获得：踝关节机械阻抗的方向变化、踝关节作为弹簧的程度以及神经贡献的独特证据。该方法通过测试由无源元件组成的简单物理“模型”进行了验证。对年轻未受损受试者的实验量化了最大放松状态下人类踝关节的行为，表明踝关节机械阻抗具有弹簧特性，但强烈依赖于方向，在内翻时最弱。值得注意的是，如果受试者没有完全放松，该分析对偏离弹簧行为的细微但具有统计学意义的偏差具有足够的敏感性。这种方法可能会为了解正常和生物力学或神经损伤后的踝关节功能提供新的见解。
