Motor strategies for initiating downward-oriented movements during standing in adults
Motor strategies for initiating downward-oriented movements during standing in adults
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DOI：
10.1007/s00221-004-1875-4
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发表时间：
2004-09-01
影响因子：
2
通讯作者：
Chino, N
中科院分区：
文献类型：
--
作者：
Hase, K;Sako, M;Chino, N
坐下和蹲下是日常生活中的常规活动，通过弯曲躯干和腿部来降低体重，但它们显然需要不同的运动策略来实现每个目标姿势。前一个动作必须将支撑表面转移到座位上，而后者必须将质心保持在双脚的同一基部内。通过比较这两种动作的性能，在启动向下定向运动的机制和优化的过程中，他们的重复性能进行了研究。12名健康受试者被要求在灯光提示下立即进行坐下和蹲下动作，但要以自然速度进行。在每次任务之前和期间记录肌电图、右腿关节的角运动和压力中心（COP）位移。分别分析了从直立姿势开始中断的初始机制和重复运动过程中姿势调整的变化。坐下来的运动是通过一个刻板的运动策略，其特征是腓肠肌爆发加上竖脊肌失活。前者产生了一个短暂的COP位移在前进的方向，并同时解锁的行李箱防止了下跌落后。相比之下，由于不需要在给定方向上产生动力，因此可以使用各种运动策略来启动蹲下。初始COP位移的方向，以启动蹲不同的肌肉参与解锁直立姿势。在重复坐下期间，在第二次试验后，准备期初始站立姿势的平均COP位置立即向前移动。同时，在后来的试验中，竖脊肌在早期被停用。当受试者将自己转移到座位上时，这些导致向后方向的动量减少。然而，在下蹲任务中，除了在第一次试验中站立时膝关节轻微弯曲外，无法识别这些变化。这些结果表明，在转移的身体质量的情况下，另一个支持基地的中枢神经系统立即调整的初始动力的大小，以优化性能。
Sitting down and squatting are routine activities in daily living that lower the body mass by flexing the trunk and legs, but they obviously require different motor strategies for each goal posture. The former action must transfer the supporting surface onto a seat, whereas the latter must maintain the center of mass within the same base of both feet. By comparing the performance of both maneuvers, the mechanisms involved in initiating the downward-oriented movements and the process of optimizing the performance during their repetitions were studied. Twelve healthy subjects were asked to perform sitting-down and squatting actions immediately when a light cue was given, but at a natural speed. Electromyograms, angular movements of the joints of the right leg, and center of pressure (COP) displacement were recorded before and during each task. The initial mechanisms to initiate the break from the upright posture and the changes of postural adjustments during repetitive movements were analyzed separately. The sitting-down movement was achieved by a stereotyped motor strategy characterized by a gastrocnemius muscle burst coupled with deactivation of the erector spinae muscle. The former produced a transient COP displacement in the forward direction, and simultaneous unlocking of the trunk prevented a fall backward. By contrast, because of the absence of any need to produce momentum in a given direction, a variety of motor strategies were available to initiate squatting. The direction of initial COP displacement to initiate squatting varied with the muscles involved in unlocking the upright posture. During repetition of sitting down, the average COP position of the initial standing posture in the preparatory period was immediately shifted forward after the second trial. Simultaneously, the erector spinae muscle was deactivated earlier in the later trials. These resulted in a decreased momentum in the backward direction while the subjects were transferring themselves onto the seat. In the squatting task, however, these changes could not be identified, except for a slight flexed position of the knee during standing in the first trial. These findings suggest that in the case of transferring the body-mass to another supporting base the central nervous system immediately adjusts the size of the initial impetus to optimize the performance.