Neural Mechanisms in Muscle Fatigue

肌肉疲劳的神经机制

• 批准号: 6457465
• 负责人: ROGER M. ENOKA
• 金额: $ 30.59万
• 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/6457465
• 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.

肌肉的耐力能力随执行的任务而异。我们发现，与支撑等效惯性载荷相比，腕部屈肌的耐耐力时间是肘部屈肌的耐力时间是力传感器的两倍。尽管受试者在支撑惯性载荷时被力传感器限制并保持恒定的肘部角度时，受试者具有恒定的力，但所得的肌肉扭矩和平均EMG的增加速率对于这两个任务是相同的。尽管如此，其他结果表明，在恒定位置收缩期间，向运动神经元的下降驱动力更大。我们假设肘部屈肌的耐力时间比恒定的位置收缩较少，而与恒定的抗衡收缩相比，由于对运动神经元的兴奋性下降驱动力更大，并且来自肌肉的抑制作用更大。根据这一假设，这两个任务的耐力时间差异归因于脊柱运动神经元接收到的输入的差异。我们提出了三个特定的目标（目标1到3），以检查假设的下降驱动成分和两个目的（目标4和5）以评估抑制反馈组件。该假设预测，在恒定位置收缩期间，运动单位活性将更大（AIM 1），并且当增加位置反馈信号的增益增加（AIM 2）并将振动应用于活动肌肉时（AIM 3），耐力时间将是卫生的。此外，该假设预测，对侧肌肉中运动单位的最大排放率下降（AIM 4），并且在恒定位置收缩后，平均动脉压的增加（AIM 5）将更大。我们不知道另一项研究研究了神经机制对在恒定和恒定位置等距收缩期间经历的疲劳的贡献。结果将提供有关等距收缩期间生理调整的新信息，这是最常见的肌肉活动形式，并将直接应用于人体工程学中的工作任务以及在康复中的体育活动处方。