van der Fits I B, Klip A W, van Eykern L A, Hadders-Algra M
Department of Medical Physiology, University of Groningen, The Netherlands.
Exp Brain Res. 1998 May;120(2):202-16. doi: 10.1007/s002210050394.
The present study evaluated the effect of different positions, which varied in the amount of bodily support, on postural control during fast pointing movements. Fourteen adult subjects were studied in standing, various sitting and lying positions. Multiple surface electromyograms (EMGs) of arm, neck, trunk and upper leg muscles and kinematics were recorded during a standard series of unilateral arm movements. Two additional series, consisting of bilateral arm movements and unilateral arm movements with an additional weight, were performed to assess whether additional task-load affected postural adjustments differently in a sitting and standing position. Two pointing strategies were used--despite identical instructions. Seven subjects showed an elbow extension throughout the movements. They used the deltoid (DE) as the prime mover (DE group). The other seven subjects performed the movement with a slight elbow flexion and used the biceps brachii (BB) as the prime mover (BB group). The two strategies had a differential effect on the postural adjustments: postural activity was less and substantially later in the BB-group than in the DE group. Anticipatory postural muscle activity was only present in the DE group during stance. In all positions and task-load conditions the dorsal postural muscles were activated before their ventral antagonists. The activation rate, the timing and--to a lesser extent the amplitude of the dorsal muscle activity was position dependent. The position dependency was mainly found in the caudally located lumbar extensor (LE) and hamstrings (HAM) muscles. The EMG amplitude of LE and HAM was also affected by body geometry (trunk and pelvis position). Position and body geometry had only a minor effect on the activity of the neck and thoracic extensor muscles. This difference in behaviour of lower and upper postural muscles suggests that they could serve different postural tasks: the lower muscles being more involved in keeping the centre of mass within the limits of the support surface, and the upper ones in counteracting the reaction forces generated by movement onset. Increasing task-load by performing bilateral movements and--to a minor extent--during loaded unilateral movements affected the temporal and quantitative characteristics of the postural adjustments during standing and sitting in a similar way. The effect was present mainly during the early part of the response (within 100 ms after prime mover onset). This suggests that feedforward or anticipatory mechanisms play a major role in the task-specific modulation of postural adjustments.
本研究评估了不同体位（身体支撑量不同）对快速指向运动中姿势控制的影响。对14名成年受试者在站立、不同坐姿和躺姿下进行了研究。在一系列标准的单侧手臂运动过程中，记录了手臂、颈部、躯干和大腿上部肌肉的多通道表面肌电图（EMG）以及运动学数据。还进行了另外两组实验，包括双侧手臂运动和单侧手臂负重运动，以评估额外的任务负荷在坐姿和站姿下对姿势调整的影响是否不同。尽管指令相同，但使用了两种指向策略。七名受试者在整个运动过程中表现为伸肘，他们以三角肌（DE）作为主要运动肌（DE组）。另外七名受试者在运动时肘部稍有屈曲，以肱二头肌（BB）作为主要运动肌（BB组）。这两种策略对姿势调整有不同的影响：BB组的姿势活动比DE组少且明显延迟。在站立期，预期姿势肌肉活动仅出现在DE组。在所有体位和任务负荷条件下，背部姿势肌肉在其腹侧拮抗肌之前被激活。背部肌肉活动的激活率、时间以及在较小程度上的幅度取决于体位。体位依赖性主要出现在位于尾部的腰伸肌（LE）和腘绳肌（HAM）。LE和HAM的肌电图幅度也受身体几何形状（躯干和骨盆位置）的影响。体位和身体几何形状对颈部和胸部伸肌的活动影响较小。上下部姿势肌肉的这种行为差异表明它们可能执行不同的姿势任务：下部肌肉更多地参与将质心保持在支撑面范围内，而上部肌肉则用于抵消运动开始时产生的反作用力。通过进行双侧运动增加任务负荷，以及在较小程度上在单侧负重运动期间，以类似的方式影响了站立和坐姿时姿势调整的时间和定量特征。这种影响主要出现在反应的早期（主要运动肌开始后100毫秒内）。这表明前馈或预期机制在姿势调整的任务特异性调节中起主要作用。
