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.

肌肉的耐力能力随所执行的任务而变化。我们发现，当手腕连接到力传感器上时，肘屈肌进行次最大等长收缩的耐力时间是支撑同等惯性载荷时的两倍。虽然受试者在手腕被力传感器约束时保持恒定的力，在支撑惯性载荷时保持恒定的肘角，但在这两项任务中，合成的肌肉扭矩和平均肌电的增加率是相同的。尽管如此，额外的结果表明，在恒定位置收缩期间，对运动神经元的下行驱动更大。我们假设，与恒定力收缩相比，恒位收缩时肘屈肌的耐力时间更短，这是因为对运动神经元的兴奋性下行驱动更大，肌肉的抑制反馈更大。根据这一假说，这两项任务的耐力时间的差异可归因于脊髓运动神经元接收的输入的不同。我们提出了三个具体的目标(目标1到3)来检验假设的下降驱动成分，并提出了两个目标(目标4和5)来评估抑制反馈成分。该假说预测，在恒定位置收缩(目标1)期间，运动单位的活动将更大，而当位置反馈信号的增益增加(目标2)和对活动肌肉施加振动(目标3)时，耐力时间将更短。此外，该假说预测，在恒定位置收缩后，对侧肌肉运动单位的最大放电率下降(目标4)，平均动脉压(目标5)的增加将更大。我们还没有发现另一项研究考察了恒力和恒位等长收缩过程中神经机制对疲劳的影响。研究结果将提供有关等长收缩期间发生的生理调节的新信息，等长收缩是肌肉活动的最常见形式，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。