title: Neuromuscular Fatigue during Prolonged Exercise in Hypoxia.
abstract: Prolonged cycling exercise performance in normoxia is limited because of both peripheral and central neuromuscular impairments. It has been reported that cerebral perturbations are greater during short-duration exercise in hypoxia compared with normoxia. The purpose of this study was to test the hypothesis that central deficits are accentuated in hypoxia compared with normoxia during prolonged (three bouts of 80 min separated by 25 min) whole-body exercise at the same relative intensity.
  
  
  
  Ten subjects performed two sessions consisting of three 80-min cycling bouts at 45% of their relative maximal aerobic power in normoxia and hypoxia (FiO2 = 0.12). Before exercise and after each bout, maximal voluntary force, voluntary activation assessed with nerve stimulation and transcranial magnetic stimulation, corticospinal excitability (motor evoked potential), intracortical inhibition (cortical silent period), and electrical (M-wave) and contractile (twitch and doublet peak forces) properties of the knee extensors were measured. Prefrontal and motor cortical oxygenation was also recorded during each cycling bout in both conditions.
  
  
  
  A significant but similar force reduction (≈-22%) was observed at the end of exercise in normoxia and hypoxia. The modifications of voluntary activation assessed with transcranial magnetic stimulation and nerve stimulation, motor evoked potential, cortical silent period, and M-wave were also similar in both conditions. However, cerebral oxygenation was reduced in hypoxia compared with normoxia.
  
  
  
  These findings show that when performed at the same relative low intensity, prolonged exercise does not induce greater supraspinal fatigue in hypoxia compared with normoxia. Despite lower absolute exercise intensities in hypoxia, reduced brain O2 availability might contribute to similar amounts of central fatigue compared with normoxia.
authors.affiliation: 1Laboratory HP2, Grenoble Alpes University, Grenoble, FRANCE; 2INSERM U1042, Grenoble, FRANCE; 3Laboratory "Movement, Interactions, Performance" (EA 4334), Faculty of Sport Sciences, University of Nantes, Nantes, FRANCE; 4Inter-university Laboratory of Human Movement Biology, University Savoie Mont Blanc, Chambéry, FRANCE; 5Inter-university Laboratory of Human Movement Biology, University of Lyon, UJM-Saint-Etienne, Saint-Etienne, FRANCE; 6Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, CANADA; and 7EuroMov, University of Montpellier, FRANCE.
authors.forename: Marc
authors.initials: M
authors.lastname: Jubeau
authors.forename: Thomas
authors.initials: T
authors.lastname: Rupp
authors.forename: John
authors.initials: J
authors.lastname: Temesi
authors.forename: Stéphane
authors.initials: S
authors.lastname: Perrey
authors.forename: Bernard
authors.initials: B
authors.lastname: Wuyam
authors.forename: Guillaume Y
authors.initials: GY
authors.lastname: Millet
authors.forename: Samuel
authors.initials: S
authors.lastname: Verges
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005267:Femoral Nerve / Q000502:physiology; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology; D007719:Knee Joint / Q000502:physiology; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology*; D017397:Prefrontal Cortex / Q000502:physiology*; D019265:Spectroscopy, Near-Infrared; D050781:Transcranial Magnetic Stimulation