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

人类中枢神经系统（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，对于人类移动，大脑激活脑干和脊髓内的运动回路，这激活神经细胞（即脊髓运动神经元），这些神经细胞投射到并激活骨骼肌。当我们开始执行一个动作时，大脑和脊髓的兴奋性会增加。大脑和脊髓被激活的方式取决于人体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。这已经在等长收缩和等张收缩后显示。在某种程度上，体力消耗减少是由于肌肉激活减少，皮质脊髓（脊髓上和脊髓）兴奋性改变和疼痛受体反馈增加。然而，很少有人知道神经肌肉疲劳是如何在高强度的节奏运动。在接下来的5年里，我实验室的研究将采取一种机械的方法来发现运动输出是如何改变的，因为在最大的手臂循环短跑过程中神经肌肉疲劳的发展。在第一阶段，我们将确定手肘屈肌在这种疲劳的发展中的作用，并确定手臂曲柄类型是否改变这种疲劳。在第二阶段，我们将确定运动训练如何影响手臂自行车短跑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。 我们的研究结果有可能不仅有助于我们了解基本的神经生理学基础的人类神经肌肉疲劳的手肘屈肌和伸肌在手臂循环短跑，但也可能证明有助于了解神经肌肉疲劳机制。研究结果可能对运动训练、运动医学、职业安全和身体损伤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.