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

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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.