Ambike S, Zhou T, Zatsiorsky V M, Latash M L
Department of Kinesiology, The Pennsylvania State University, University Park, PA, USA.
Department of Kinesiology, The Pennsylvania State University, University Park, PA, USA.
Neuroscience. 2015 Jul 9;298:336-56. doi: 10.1016/j.neuroscience.2015.04.023. Epub 2015 Apr 18.
This study used the framework of the referent configuration hypothesis and slow changes in the external conditions during vertical oscillation of a hand-held object to infer the characteristics of hypothetical control variables. The study had two main objectives: (1) to show that hypothetical control variables, namely, referent coordinates and apparent stiffness of vertical hand position and grip force can be measured in an experiment; and (2) to establish relation(s) between these control variables that yield the classic grip-force-load-force coupling. Healthy subjects gripped a handle and performed vertical oscillations between visual targets at one of five metronome-prescribed frequencies. A HapticMaster robot was used to induce slow changes in the vertical force applied to the handle, while the size of the handle was changed slowly leading to changes in the grip aperture. The subjects were instructed not to react to possible changes in the external forces. A linear, second-order model was used to reconstruct the referent coordinate and apparent stiffness values for each phase of the vertical oscillation cycle using across-cycle regressions. The reconstructed time profiles of the referent coordinates and apparent stiffness showed consistent trends across subjects and movement frequencies. To validate the method, these values were used to predict the vertical force and the grip force applied to the handle for movement cycles that were not utilized in the reconstruction process. Analysis of the coupling between the four variables, two referent coordinates and two apparent stiffness values, revealed a single strong constraint reflecting the coupling between the grip force and vertical force. We view these data as providing experimental support for the idea of controlling natural, multi-muscle actions with shifts in a low-dimensional set of referent coordinates.
本研究采用参照构型假说的框架以及手持物体垂直振荡过程中外在条件的缓慢变化，来推断假设控制变量的特征。该研究有两个主要目标：（1）证明在实验中可以测量假设控制变量，即垂直手部位置和握力的参照坐标及表观刚度；（2）建立这些控制变量之间的关系，以产生经典的握力 - 负载力耦合。健康受试者握住一个手柄，并在五个节拍器规定频率之一的视觉目标之间进行垂直振荡。使用触觉主机器人来诱导施加在手柄上的垂直力缓慢变化，同时缓慢改变手柄大小以导致握距变化。受试者被指示不要对外力的可能变化做出反应。使用线性二阶模型，通过跨周期回归来重建垂直振荡周期每个阶段的参照坐标和表观刚度值。重建的参照坐标和表观刚度的时间曲线在受试者和运动频率之间显示出一致的趋势。为了验证该方法，这些值被用于预测在重建过程中未使用的运动周期施加在手柄上的垂直力和握力。对四个变量（两个参照坐标和两个表观刚度值）之间的耦合分析揭示了一个单一的强约束，反映了握力和垂直力之间的耦合。我们认为这些数据为通过低维参照坐标集的变化来控制自然多肌肉动作的观点提供了实验支持。
