Neural Mechanisms in Muscle Fatigue

肌肉疲劳的神经机制

• 批准号: 6730614
• 负责人: ROGER M. ENOKA
• 金额: $ 27.62万
• 依托单位: UNIVERSITY OF COLORADO
• 依托单位国家: 美国
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-04-15 至 2005-03-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6730614
• 关键词: action potentials; adolescence (12-20); adult human (21+); afferent nerve; biomechanics; clinical research; efferent nerve; elbow; electrodes; electromyography; exercise; fatigue; human subject; motor neurons; muscle contraction; muscle function; neuromuscular junction; neuromuscular system; statistics /biometry; striated muscles; vital statistics; wrist

The endurance capacity of muscle varies with the task that is performed. We found that the endurance time for a submaximal isometric contraction with the elbow flexor muscles was twice as long when the wrist was attached to a force transducer compared with when it supported an equivalent inertial load. Although the subject sustained a constant force when the wrist was restrained by a force transducer and maintained a constant elbow angle when supporting the inertial load, the resultant muscle torque and the rate of increase in the average EMG were identical for the two tasks. Nonetheless, additional results suggested that the descending drive to the motor neurons was greater during the constant-position contraction. We hypothesize that endurance time of the elbow flexor muscles is less for a constant- position contraction compared with a constant-force contraction due to greater excitatory descending drive to the motor neurons and greater inhibitory feedback from the muscles. According to this hypothesis, the difference in endurance time for the two tasks is attributable to differences in the input received by the spinal motor neurons. We propose three specific aims (Aims 1 to 3) to examine the, descending- drive component of the hypothesis and two aims (Aims 4 and 5) to assess the inhibitory-feedback component. The hypothesis predicts that motor unit activity will be greater during the constant-position contraction (Aim 1) and that endurance time will be briefer when the gain of the position-feedback signal is increased (Aim 2) and vibration is applied to the active muscles (Aim 3). Furthermore, the hypothesis predicts that the decline in maximum discharge rate of motor units in the contralateral muscles (Aim 4) and that the increase in mean arterial pressure (Aim 5) will be greater after the constant-position contraction. We are not aware of another study that has examined the contribution of neural mechanisms to the fatigue experienced during constant-force and constant-position isometric contractions. The outcomes will provide novel information on the physiological adjustments that occur during isometric contractions, which are the most common form of muscle activity, and will have direct application to the design of work tasks in ergonomics and the prescription of physical activities in rehabilitation.

肌肉的耐力随着所执行的任务而变化。我们发现，当手腕连接到力传感器时，手肘屈肌肌肉的次最大等长收缩的耐力时间是支撑等效惯性负载时的两倍。虽然受试者在手腕被力传感器约束时持续恒定的力，并且在支撑惯性负载时保持恒定的肘部角度，但是所产生的肌肉扭矩和平均EMG的增加率对于两个任务是相同的。尽管如此，额外的结果表明，在恒定位置收缩期间，运动神经元的下行驱动更大。我们假设手肘屈肌的耐力时间是一个恒定的位置收缩相比，恒定的力量收缩，由于更大的兴奋性下降驱动运动神经元和更大的抑制性反馈的肌肉。根据这一假设，两种任务的耐受时间的差异可归因于脊髓运动神经元接收的输入的差异。我们提出了三个具体的目标（目标1至3），以检查假设的下降驱动组件和两个目标（目标4和5），以评估的反馈组件。该假设预测，运动单位的活动将是更大的在恒定位置的收缩（目标1），耐力时间将是短暂的位置反馈信号的增益增加（目标2）和振动施加到活动的肌肉（目标3）。此外，该假设预测，在对侧肌肉的运动单位的最大放电率的下降（目的4）和平均动脉压的增加（目的5）将在恒定位置收缩后更大。我们不知道另一项研究，已审查了神经机制的贡献，在恒定的力量和恒定的位置等长收缩期间经历的疲劳。这些结果将提供有关等长收缩（肌肉活动的最常见形式）期间发生的生理调整的新信息，并将直接应用于人体工程学中的工作任务设计和康复中的体力活动处方。