An examination of fatigue development during intense motor output(s)

人类的中枢神经系统(即大脑和脊髓)及其如何产生和适应不同的肌肉收缩和运动模式是非常复杂的。一般来说，对于人类的运动，大脑激活脑干和脊髓内的运动回路，从而激活投射到骨骼肌并激活骨骼肌的神经细胞(即脊髓运动神经元)。当我们开始执行一个动作时，大脑和脊髓的兴奋性就会增加。大脑和脊髓的激活方式取决于人类运动的类型和疲劳状态。随着神经肌肉疲劳的增加，我们的体力活动能力大大降低。在等长收缩和等张收缩之后，这一点已经显示出来。体力消耗减少的部分原因是肌肉活动减少，皮质脊髓(棘上和脊髓)兴奋性改变，以及来自疼痛感受器的反馈增加。然而，关于神经肌肉疲劳是如何在高强度有节奏的运动中发展起来的，我们知之甚少。在接下来的5年里，我的实验室的研究将采用机械学的方法来发现在最大限度的手臂自行车冲刺过程中，由于神经肌肉疲劳的发展，运动输出是如何改变的。在第一阶段，我们将确定肘屈肌在这种疲劳的发展中的作用，并确定手臂摇动类型是否改变了这种疲劳。在第二阶段，我们将确定运动训练如何影响手臂自行车冲刺过程中神经肌肉疲劳的发展。在每个阶段，我们将使用一系列新的刺激范例来发现周围神经系统(即骨骼肌特性)和中枢神经系统(即皮质脊髓兴奋性)特性的变化。我们的研究结果不仅有可能有助于我们理解人类在手臂自行车冲刺过程中肘屈肌和伸肌的神经肌肉疲劳的基本神经生理学，而且还可能被证明有助于理解神经肌肉疲劳的机制。其结果可能会对运动训练、运动医学、职业安全和身体残疾等产生广泛的潜在影响。

The human central nervous system (i.e. brain and spinal cord) and how it functions to produce, and adapt to, different patterns of muscle contractions and movement is very complex. Generally speaking, for humans to move, the brain activates motor circuitry within the brainstem and spinal cord, which activates nerve cells (i.e. spinal motoneurones) that project to and activate skeletal muscle. When we start to execute a movement there is an increase in the excitability in the brain and spinal cord. The manner in which the brain and spinal cord are activated depends on the type of human movement and fatigue status. With increased neuromuscular fatigue our ability to physically exert is substantially reduced. This has been shown following isometric and isotonic contractions. In part, the reduced physical exertion is due to decreased muscle activation, altered corticospinal (supraspinal and spinal) excitability and increased feedback from our pain receptors. However, very little is known about how neuromuscular fatigue is developed during high-intensity rhythmic movements. Over the next 5 years, studies from my lab will take a mechanistic approach to discover how motor output is altered due to the development of neuromuscular fatigue during maximal arm-cycling sprints. In phase 1, we will determine the role of the elbow flexors in the development of this fatigue and determine if arm-cranking type alters this fatigue. In phase 2, we will determine how exercise training affects the development of neuromuscular fatigue during arm-cycling sprints. In each phase we will be using a series of novel stimulation paradigms to discover changes in the peripheral nervous system (i.e. skeletal muscle properties) and central nervous system (i.e. corticospinal excitability) properties. Our outcomes have the potential to contribute not only to our understanding of basic neurophysiology underlying human neuromuscular fatigue of the elbow flexors and extensors during arm-cycling sprints, but may also prove useful in understanding neuromuscular fatigue mechanisms. The outcomes may have broad potential impacts such as on sports training, sports medicine, occupational safety, and physical impairments, etc.