title: Carbon monoxide inhalation reduces skeletal muscle fatigue resistance.
abstract: OBJECTIVE
  To determine whether inhalation of carbon monoxide (CO), resulting in carboxyhaemoglobin (COHb) levels observed in smokers, had an effect on muscle fatigue during electrically evoked and voluntary muscle contractions.
  
  
  METHODS
  Young non-smoking males inspired CO from a Douglas bag until their COHb level reached 6%. During the control condition the same participants inspired ambient air from a Douglas bag for 6 min. Fatigue was assessed as the decline in torque in isometric knee extensions, during 2 min of electrically evoked contractions (30 Hz, 1 s on, 1 s off) and during 2 min of maximal isometric voluntary contractions (1 s on, 1 s off). A fatigue index (FI) was calculated as the ratio of final torque : initial torque. Time to peak torque (TPT) and half relaxation time ((1/2)RT) were also determined for the electrically evoked contractions.
  
  
  RESULTS
  The FI during both the voluntary fatigue test (control: 0.80 +/- 0.09 vs. CO: 0.70 +/- 0.08; mean +/- SD) and that of the fatigue test with electrically evoked contractions (control: 0.61 +/- 0.09 vs. CO: 0.53 +/- 0.12) was significantly lower after CO inhalation than after inhalation of ambient air (P < 0.05). There was, however, no effect of CO on the changes in TPT or (1/2)RT during the fatigue test.
  
  
  CONCLUSIONS
  Carbon monoxide inhalation resulting in COHb levels found in smokers has an acute impact on the ability of the muscle to resist fatigue.
authors.affiliation: Institute for Biophysical and Clinical Research into Human Movement (IRM), Manchester Metropolitan University, Cheshire, UK. c.morse@mmu.ac.uk
authors.forename: C I
authors.initials: CI
authors.lastname: Morse
authors.forename: L J
authors.initials: LJ
authors.lastname: Pritchard
authors.forename: R C I
authors.initials: RC
authors.lastname: Wüst
authors.forename: D A
authors.initials: DA
authors.lastname: Jones
authors.forename: H
authors.initials: H
authors.lastname: Degens
mesh_terms: D000280:Administration, Inhalation; D000328:Adult; D002248:Carbon Monoxide / Q000008:administration & dosage*; D002263:Carboxyhemoglobin / Q000032:analysis; D004576:Electromyography; D006801:Humans; D019570:Inhalation Exposure; D007537:Isometric Contraction / Q000502:physiology; D007719:Knee Joint / Q000502:physiology; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D005082:Physical Exertion / Q000187:drug effects* / Q000502:physiology
chemical_list: D002248:Carbon Monoxide; D002263:Carboxyhemoglobin