Levin Oron, Wenderoth Nicole, Steyvers Maarten, Swinnen Stephan P
Department of Kinesiology, Group Biomedical Sciences, Katholieke Universiteit Leuven, Tervuurse Vest 101, 3001 Leuven, Belgium.
Exp Brain Res. 2003 Jan;148(1):62-76. doi: 10.1007/s00221-002-1277-4. Epub 2002 Nov 9.
In the present study, we investigated the influence of external force manipulations on movements in different directions, while keeping the amplitude invariant. Subjects ( n=10) performed a series of cyclical anteroposterior, mediolateral, and oblique line-drawing movements (star drawing task) with their dominant limb in the horizontal plane. To dissociate kinematics from the underlying patterns of muscle activation, spring loading was applied to the forearm of the moving limb. Whereas spring loading of the arm resulted in considerable changes in the overall amount of muscle activation in the elbow and shoulder muscles, invariance was largely maintained at the kinematic level. Subjects produced the required movement directions and amplitudes of the star drawing largely successfully, irrespective of the force bias induced by the spring. These observations demonstrate motor equivalence and strengthen the notion that the spatial representation of drawing movements is encoded in the higher brain regions in a rather abstract form that is dissociated from the concrete muscle activation patterns underlying a particular movement direction. To achieve this goal, the central nervous system shifted between two or more muscle grouping strategies to overcome modulations in the interaction among posture-dependent (joint stiffness), dynamic (inertial), and elastic (spring) torque components in the joints. Spring loading induced general changes in the overall amount of EMG activity, which was largely muscle but not direction specific, presumably to represent the posture-dependent biasing force of the spring. Loading was mainly shown to increase muscle coactivation in the elbow joint. This indicates that the subjects tended to increase stiffness in the elbow to compensate for changes in the spring bias forces in order to minimize trajectory errors. Changes in muscle grouping of the shoulder antagonists were mainly a consequence of movement direction but were also affected partly by loading, presumably reflecting the influence of dynamic force components. Taken together, the results confirmed the hypothesis that changes of movement direction and direction of force in the end-effector generated specific sets of muscle grouping to overcome the dynamic requirements in the joints while keeping the kinematics largely unchanged. This suggests that directional tuning in muscle activity and changes in muscle grouping reflects the formation of appropriate internal models in the CNS that give rise to motor equivalence.
在本研究中，我们在保持运动幅度不变的情况下，研究了外力操纵对不同方向运动的影响。受试者（n = 10）用其优势肢体在水平面内进行一系列周期性的前后、内外侧和斜线绘制运动（星形绘制任务）。为了将运动学与肌肉激活的潜在模式区分开来，对运动肢体的前臂施加弹簧加载。虽然手臂的弹簧加载导致肘部和肩部肌肉的肌肉激活总量发生了相当大的变化，但在运动学水平上基本保持不变。受试者基本上成功地产生了星形绘制所需的运动方向和幅度，而不管弹簧引起的力偏差如何。这些观察结果证明了运动等效性，并强化了这样一种观点，即绘制运动的空间表征以一种相当抽象的形式编码在大脑高级区域，这种形式与特定运动方向下的具体肌肉激活模式分离。为了实现这一目标，中枢神经系统在两种或更多种肌肉分组策略之间切换，以克服关节中与姿势相关（关节刚度）、动态（惯性）和弹性（弹簧）扭矩分量之间相互作用的调制。弹簧加载引起了肌电图活动总量的一般变化，这在很大程度上是肌肉特异性而非方向特异性的，大概是为了代表弹簧的与姿势相关的偏置力。加载主要表现为增加肘关节的肌肉共同激活。这表明受试者倾向于增加肘部的刚度，以补偿弹簧偏置力的变化，从而使轨迹误差最小化。肩部拮抗肌的肌肉分组变化主要是运动方向的结果，但也部分受到加载的影响，大概反映了动态力分量的影响。综上所述，结果证实了以下假设：末端执行器中运动方向和力方向的变化产生了特定的肌肉分组集，以克服关节中的动态需求，同时使运动学基本保持不变。这表明肌肉活动中的方向调整和肌肉分组的变化反映了中枢神经系统中适当内部模型的形成，从而产生了运动等效性。
