Supraspinal and segmental mechanisms of fatigue

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Neuromuscular fatigue is defined as a gradual, activity-induced reduction in the ability to generate muscle force. Athough the central nervous system has several mechanisms which function to optimize muscle activation and offset the fatigue-related decline in force, there are a number of spinal and supraspinal mechanisms of "failure" that contribute to fatigue. For the most part, spinal and supraspinal inputs that modulate muscle activation have been treated as distinct inputs and assessed independently. However, input to spinal motor neurons is largely via networks which integrate sensory input, excitatory drive from the brain, modulatory drive from brain, and the intrinsic properties that are built into the spinal motor neuron itself. The adaptability of these segmental circuits and their role in the maintenance or failure of force production has been a neglected area in the study of central fatigue. The purpose of this research program is to determine how the integration of supraspinal and afferent inputs in segmental interneuronal pathways contribute to the maintenance of voluntary drive to muscle during fatigue. This research is significant because until we understand the central mechanisms that modulate muscle output in healthy people, we cannot fully understand the mechanisms of impaired motor function in injury, ageing, and disease.