Galloway James C, Koshland Gail F
Physiological Sciences Program, University of Arizona, Tucson, AZ 85724, USA.
Exp Brain Res. 2002 Jan;142(2):163-80. doi: 10.1007/s002210100882. Epub 2001 Dec 6.
Studies of multijoint arm movements have demonstrated that the nervous system anticipates and plans for the mechanical effects that arise from motion of the linked limb segments. The general rules by which the nervous system selects appropriate muscle activities and torques to best deal with these intersegmental effects are largely unknown. In order to reveal possible rules, this study examined the relationship of muscle and interaction torques to joint acceleration at the shoulder, elbow and wrist during point-to-point arm movements to a range of targets in the horizontal plane. Results showed that, in general, dynamics differed between the joints. For most movements, shoulder muscle torque primarily determined net torque and joint acceleration, while interaction torque was minimal. In contrast, elbow and wrist net torque were determined by a combination of muscle and interaction torque that varied systematically with target direction and joint excursion. This "shoulder-centered pattern" occurred whether subjects reached targets using straight or curved finger paths. The prevalence of a shoulder-centered pattern extends findings from a range of arm movement studies including movement of healthy adults, neurological patients, and simulations with altered interaction effects. The shoulder-centered pattern occurred for most but not all movements. The majority of the remaining movements displayed an "elbow-centered pattern," in which muscle torque determined initial acceleration at the elbow and not at the shoulder. This occurred for movements when shoulder excursion was <50% of elbow excursion. Thus, both shoulder- and elbow-centered movements displayed a difference between joints but with reversed dynamics. Overall, these findings suggest that a difference in dynamics between joints is a general feature of horizontal plane arm movements, and this difference is most commonly reflected in a shoulder-centered pattern. This feature fits well with other general shoulder-elbow differences suggested in the literature on arm movements, namely that: (a) agonist muscle activity appears more closely related to certain joint kinematics at the shoulder than at the elbow, (b) adults with neurological damage display less disruption of shoulder motion than elbow motion, and (c) infants display adult-like motion first in the shoulder and last at the wrist.
对多关节手臂运动的研究表明，神经系统会预测并规划因相连肢体节段运动而产生的机械效应。神经系统选择合适的肌肉活动和扭矩以最佳应对这些节段间效应的一般规则在很大程度上尚不清楚。为了揭示可能的规则，本研究考察了在水平面内进行指向一系列目标的点对点手臂运动时，肩部、肘部和腕部的肌肉扭矩及相互作用扭矩与关节加速度之间的关系。结果表明，总体而言，各关节的动力学情况有所不同。对于大多数运动，肩部肌肉扭矩主要决定净扭矩和关节加速度，而相互作用扭矩最小。相比之下，肘部和腕部的净扭矩由肌肉扭矩和相互作用扭矩共同决定，且它们会随目标方向和关节偏移而系统地变化。无论受试者是通过直线还是曲线手指路径到达目标，这种“以肩部为中心的模式”都会出现。以肩部为中心的模式的普遍存在扩展了一系列手臂运动研究的结果，这些研究包括健康成年人、神经疾病患者的运动以及具有改变的相互作用效应的模拟。以肩部为中心的模式在大多数但并非所有运动中都会出现。其余大多数运动呈现出“以肘部为中心的模式”，即肌肉扭矩决定肘部而非肩部的初始加速度。当肩部偏移小于肘部偏移的50%时，这种情况会出现在运动中。因此，以肩部和肘部为中心的运动在关节间均表现出差异，但动力学情况相反。总体而言，这些发现表明关节间动力学差异是水平面内手臂运动的一个普遍特征，且这种差异最常见地反映在以肩部为中心的模式中。这一特征与手臂运动文献中提出的其他一般肩部 - 肘部差异非常契合，即：(a) 与肘部相比，主动肌活动似乎与肩部的某些关节运动学关系更为密切；(b) 患有神经损伤的成年人肩部运动受到的干扰比肘部运动小；(c) 婴儿最早在肩部表现出类似成人的运动，最后在腕部表现出类似成人的运动。
