Response of Spinal Excitability to Different Short-Lasting Motor Tasks: Preliminary Results

Understanding the origin of muscle fatigue is essential for optimizing neuro-rehabilitation treatments. Fatigue is tasks dependent and its neural substrates have been deeply addressed for isometric contractions. However, we recently showed differences in the silent periods generated at cortical or spinal levels after brief maximal rate finger tapping or isometric force tasks, advocating for a cortical but not spinal origin of fatigue for repetitive movements. Here we extend our previous findings by exploring another spinal cord circuits, as well as analyzing the modification of the compound muscle action potential. We use electric cervicomedullary stimulation (n = 7) and the recording of the compound muscle action potential, always at the time of fatigue. Once more our results suggest a different place of fatigue onset for each type of task. Fatigue evoked by maximal rate finger tapping does not have its origin at spinal cord level.