title: Group III/IV locomotor muscle afferents alter motor cortical and corticospinal excitability and promote central fatigue during cycling exercise.
abstract: OBJECTIVE
  To investigate the influence of group III/IV muscle afferents on the development of central fatigue and corticospinal excitability during exercise.
  
  
  METHODS
  Fourteen males performed cycling-exercise both under control-conditions (CTRL) and with lumbar intrathecal fentanyl (FENT) impairing feedback from leg muscle afferents. Transcranial magnetic- and cervicomedullary stimulation was used to monitor cortical versus spinal excitability.
  
  
  RESULTS
  While fentanyl-blockade during non-fatiguing cycling had no effect on motor-evoked potentials (MEPs), cervicomedullary-evoked motor potentials (CMEPs) were 13±3% higher (P<0.05), resulting in a decrease in MEP/CMEP (P<0.05). Although the pre- to post-exercise reduction in resting twitch was greater in FENT vs. CTRL (-53±3% vs. -39±3%; P<0.01), the reduction in voluntary muscle activation was smaller (-2±2% vs. -10±2%; P<0.05). Compared to the start of fatiguing exercise, MEPs and CMEPs were unchanged at exhaustion in CTRL. In contrast, MEPs and MEP/CMEP increased 13±3% and 25±6% in FENT (P<0.05).
  
  
  CONCLUSIONS
  During non-fatiguing exercise, group III/IV muscle afferents disfacilitate, or inhibit, spinal motoneurons and facilitate motor cortical cells. In contrast, during exhaustive exercise, group III/IV muscle afferents disfacilitate/inhibit the motor cortex and promote central fatigue.
  
  
  CONCLUSIONS
  Group III/IV muscle afferents influence corticospinal excitability and central fatigue during whole-body exercise in humans.
authors.affiliation: Department of Internal Medicine, University of Utah, Salt Lake City, Utah, United States; Discipline of Physiology, Adelaide Medical School, The University of Adelaide, Australia. Electronic address: simran.sidhu@adelaide.edu.au.
authors.forename: Simranjit K
authors.initials: SK
authors.lastname: Sidhu
authors.affiliation: Department of Exercise & Sport Science, University of Utah, Salt Lake City, Utah, United States.
authors.forename: Joshua C
authors.initials: JC
authors.lastname: Weavil
authors.affiliation: Department of Exercise & Sport Science, University of Utah, Salt Lake City, Utah, United States.
authors.forename: Tyler S
authors.initials: TS
authors.lastname: Mangum
authors.affiliation: Department of Anaesthesiology, University of Utah, Salt Lake City, Utah, United States.
authors.forename: Jacob E
authors.initials: JE
authors.lastname: Jessop
authors.affiliation: Department of Internal Medicine, University of Utah, Salt Lake City, Utah, United States; Department of Exercise & Sport Science, University of Utah, Salt Lake City, Utah, United States; Geriatric Research, Education & Clinical Center, VA Medical Center, Salt Lake City, Utah, United States.
authors.forename: Russell S
authors.initials: RS
authors.lastname: Richardson
authors.affiliation: Department of Anaesthesiology, University of Utah, Salt Lake City, Utah, United States.
authors.forename: David E
authors.initials: DE
authors.lastname: Morgan
authors.affiliation: Department of Internal Medicine, University of Utah, Salt Lake City, Utah, United States; Department of Exercise & Sport Science, University of Utah, Salt Lake City, Utah, United States; Department of Anaesthesiology, University of Utah, Salt Lake City, Utah, United States; Geriatric Research, Education & Clinical Center, VA Medical Center, Salt Lake City, Utah, United States.
authors.forename: Markus
authors.initials: M
authors.lastname: Amann
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000344:Afferent Pathways / Q000502:physiology; D001642:Bicycling / Q000502:physiology; D019054:Evoked Potentials, Motor / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D011712:Pyramidal Tracts / Q000502:physiology*; D052097:Quadriceps Muscle / Q000502:physiology*; D011897:Random Allocation; D055815:Young Adult
keywords: Brain; Central nervous system; Cervicomedullary stimulation; Neural blockade; Transcranial magnetic stimulation