Central and peripheral fatigue following non-exhaustive and exhaustive exercise of disparate metabolic demands

The development of fatigue after non-exhaustive and exhaustive exercise eliciting differing metabolic demands is poorly understood. Sixteen active males completed five cycling trials. The first trial established the lactate threshold (LT) and maximal oxygen uptake (VO2max). Two of the remaining trials were completed at a severe intensity (halfway between LT and VO2max, SI) and two at a moderate intensity (90% LT, MI). Each trial involved two non-exhaustive bouts matched for work between intensities before cycling to exhaustion. Responses to stimulation of the femoral nerve and motor cortex were determined after each bout to determine peripheral and central fatigue. Corticospinal excitability, cortical silent period (cSP), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF) were also assessed. Non-exhaustive cycling induced greater peripheral and central fatigue in the SI compared with the MI (P<0.05). At exhaustion, there was no difference between intensities; however, peripheral fatigue tended to be greater in the SI vs MI (-31% vs -17%, respectively, P=0.051). Exhaustive cycling increased SICI (24%, P<0.001) and reduced the cSP (-14%, P<0.001) in the SI, whereas ICF was reduced in the MI (-16%, P<0.001). These findings demonstrate exercise-induced metabolic stress accelerates the development of peripheral and central fatigue, and differentially influences intracortical excitability.