title: Noradrenaline Reuptake Inhibition Impairs Cortical Output and Limits Endurance Time.
abstract: To assess the neural mechanisms that limit endurance time, we compared a fatiguing task performed under the influence of reboxetine (REB), a noradrenaline reuptake inhibitor, and placebo (PLA).
  
  
  
  Nine male subjects (age = 24 ± 2 yr) participated in this study. The fatiguing task involved repeated 3-s submaximal isometric contractions of the knee extensors (∼33% maximal voluntary contraction) with a 2-s rest between each contraction and performed until task failure. Before, during, and after exercise, changes in voluntary activation, corticospinal (motor-evoked potential) and spinal excitability (Hoffman reflex), and muscle contractile properties were tested using electrical and transcranial magnetic stimulations. A psychomotor vigilance task assessed reaction time before and after exercise.
  
  
  
  Compared with PLA, REB reduced the endurance time by 15.6% (P = 0.04). The maximal voluntary contraction torque decreased to a similar extent at task failure in both conditions (P < 0.01), whereas the rate of decline was greater in REB than that in PLA (P = 0.02). The level of voluntary activation tested by transcranial magnetic stimulation and electrical stimulation decreased (P < 0.01) by 10%-15% at the end of the task, but the mean rate of decline was greater in REB (P ≤ 0.03). Although motor-evoked potential did not change during fatigue, Hoffman reflex, and electrically evoked torque decreased similarly in the PLA and REB conditions (P ≤ 0.02). After exercise, reaction time increased by 3.5% (P = 0.02) in REB but did not change in the PLA condition.
  
  
  
  These findings suggest that because of the noradrenaline reuptake inhibition, the output from the motor cortex is decreased at a greater rate than that in the PLA condition, contributing thereby to shorten endurance time.
authors.affiliation: 1Laboratory of Applied Biology, ULB Neuroscience Institute, Université Libre de Bruxelles (ULB), Brussels, BELGIUM; 2Department of Human Physiology, Vrije Universiteit Brussel, Brussels, BELGIUM; 3School of Public Health, Tropical Medicine and Rehabilitation Sciences, James Cook University, Queensland, AUSTRALIA; and 4Fund for Scientific Research Flanders (FWO), Brussels, BELGIUM.
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Klass
authors.forename: Jacques
authors.initials: J
authors.lastname: Duchateau
authors.forename: Samuel
authors.initials: S
authors.lastname: Rabec
authors.forename: Romain
authors.initials: R
authors.lastname: Meeusen
authors.forename: Bart
authors.initials: B
authors.lastname: Roelands
mesh_terms: D018759:Adrenergic Uptake Inhibitors / Q000494:pharmacology*; D004558:Electric Stimulation; D004576:Electromyography; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction / Q000187:drug effects / Q000502:physiology; D007717:Knee / Q000502:physiology; D008297:Male; D009025:Morpholines / Q000494:pharmacology*; D009044:Motor Cortex / Q000187:drug effects* / Q000502:physiology; D018763:Muscle Fatigue / Q000187:drug effects* / Q000502:physiology; D010465:Perception; D010807:Physical Endurance / Q000187:drug effects* / Q000502:physiology; D005082:Physical Exertion; D011712:Pyramidal Tracts / Q000187:drug effects* / Q000502:physiology; D000077593:Reboxetine; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
chemical_list: D018759:Adrenergic Uptake Inhibitors; D009025:Morpholines; D000077593:Reboxetine