Mechanisms of Centrally-Mediated Skeletal Muscle Fatigue: Small Fibers Have a Big Impact

Fatigue of intact skeletal muscle is the failure of a muscle to generate maximal force resulting from sustained exercise. Many theories regarding the etiology of muscle fatigue have been described, and they most likely all play a role in reducing the force-generating capacity of muscle following exercise. This paper describes the evidence behind fatigue stemming from the reduction of motor cortical drive to skeletal muscle in response to communication from type III/IV sensory afferent neurons. Studies demonstrate that these nerves are activated in response to increased concentrations of metabolic byproducts in skeletal muscle, mechanical stimulation from muscle contraction, and thermal energy. Their downstream effects impact the activity of the motor cortex and ability of the corticospinal tract to conduct electrical signals to lower motor neurons