ORGANIZING PRINCIPLES FOR SINGLE-JOINT MOVEMENTS .4. IMPLICATIONS FOR ISOMETRIC CONTRACTIONS
ORGANIZING PRINCIPLES FOR SINGLE-JOINT MOVEMENTS .4. IMPLICATIONS FOR ISOMETRIC CONTRACTIONS
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DOI：
10.1152/jn.1990.64.3.1033
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发表时间：
1990-09-01
影响因子：
2.5
通讯作者：
GOTTLIEB, GL
中科院分区：
文献类型：
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作者：
CORCOS, DM;AGARWAL, GC;GOTTLIEB, GL
1.正常人受试者在手肘周围进行等长脉冲和步进收缩，以视觉定义不同幅度和不同速率的目标扭矩。我们测量了两个激动剂和两个拮抗剂肌肉的关节扭矩和肌电图（EMG）。2.当任务规范要求受试者明确改变扭矩增加的速率时，激动剂和拮抗剂EMG爆发的上升速率与扭矩的上升速率共变。对于扭矩脉冲，运动神经元兴奋的持续时间随着任务定义的收缩事件的持续时间而变化。3.当受试者被要求产生不同幅度的扭矩而不指定时间间隔时，扭矩幅度与EMG上升的时间呈正相关，因此与EMG上升的高度呈正相关。受试者通常成比例地改变激动剂和拮抗剂收缩的强度，但不限于这样做。一些受试者使用与激动剂收缩相反地改变拮抗剂的策略。4.我们扩展的组织原则控制运动的一个单一的关节等长扭矩的控制。这些规则指出，控制一个单一的联合扭矩行使的两种策略之一：速度敏感的策略调制收缩率上升，通过改变运动神经元池兴奋的强度。速度不敏感策略改变收缩上升的持续时间，但不改变收缩率。这两种扭矩模式分别来自运动神经元池兴奋的脉冲高度和脉冲宽度调制。5.由于在这些条件下我们观察到的扭矩模式范围更广，因此等长收缩的速度敏感和速度不敏感运动策略的定义规则被拓宽。我们提出了一个步骤的激励组件，用于延长等长的步骤收缩和缓慢上升的斜坡模式的兴奋的收缩，发展超过几百毫秒。6.策略的选择是基于特定任务的扭矩要求。控制扭矩以产生运动的两种策略同样适用于等长扭矩的控制。然而，与运动不同的是，等长任务通常是由两种模式的混合控制的。可能的原因进行了讨论。
1. Normal human subjects made isometric pulse and step contractions about the elbow to visually defined target torques of different amplitudes and at different rates. We measured joint torque and electromyograms (EMG) from two agonist and two antagonist muscles. 2. When the task specification requires that the subject explicitly alter the rate at which torque is increased, the rates of rise of the agonist and antagonist EMG bursts covary with the rate of rise of the torque. For pulses of torque the duration of motoneuron excitation varies with the duration of the task-defined contractile event. 3. When a subject is asked to generate torques of different amplitudes without specifying a time interval, torque amplitude is positively correlated with how long, and therefore how high, the EMG rose. Subjects usually proportionately covary the strength of the agonist and antagonist contractions but are not constrained to do so. Some subjects use a strategy of varying the antagonist inversely with the agonist contraction. 4. We extend the organizing principles for the control of movement about a single joint to the control of isometric torque. These rules state that control of torque about a single joint is exercised by one of two strategies: the speed-sensitive strategy modulates the rate at which contraction rises by varying the intensity of motoneuron-pool excitation. The speed-insensitive strategy varies the duration over which contraction rises but does not change the rate. These two respective patterns of torque emerge from pulse-height and pulse-width modulation of motoneuron-pool excitation. 5. The rules defining speed-sensitive and speed-insensitive strategies for movements are broadened for isometric contractions because of the wider range of torque patterns that we observe under these conditions. We propose a step-excitation component for prolonged isometric step contractions and slowly rising ramp patterns of excitation for contractions that develop over several hundreds of milliseconds. 6. The choice of strategies is based on task-specific torque requirements. The same two strategies that control torque to produce movement apply to the control of isometric torque. Unlike movements, however, isometric tasks are more often controlled by a blending of the two patterns. Possible reasons for this are discussed.