title: Neuromuscular fatigue and exercise capacity in fibromyalgia syndrome.
abstract: OBJECTIVE
  To assess quadriceps strength and fatigability by using femoral nerve magnetic stimulation (FNMS) and their relationship to exercise capacity in patients with fibromyalgia syndrome (FMS) and healthy controls.
  
  
  METHODS
  Twenty-two women (11 with FMS, 11 controls) performed a maximal incremental cycling test and a quadriceps fatigue test on 2 separate visits. For quadriceps assessment, we used FNMS during and after maximum voluntary contraction (MVC) to evaluate central and peripheral factors of neuromuscular fatigue. Subjects performed sets of 10 intermittent (5 seconds on/5 seconds off) isometric contractions starting at 10% MVC, in 10% MVC increments from one set to another until exhaustion. Neuromuscular fatigue was assessed with FNMS after each set.
  
  
  RESULTS
  FMS patients had reduced initial MVC compared to controls (mean ± SD 102 ± 18 versus 120 ± 24 Nm; P < 0.05) without significant impairment of voluntary activation (mean ± SD 93.5% ± 3.0% versus 93.1% ± 3.4%; P = 0.74). During the fatigue task, FMS patients exhibited a greater fall in evoked muscular responses (mean ± SD -26% ± 6% versus -16% ± 8% at set 50% MVC; P < 0.05), but not in MVC (mean ± SD -24% ± 7% versus -19% ± 4% at set 50% MVC; P = 0.12). During the cycling test, FMS patients had lowered maximal exercise capacity and an enhanced rate of perceived exertion (RPE) compared to controls. The percent reduction in evoked muscular responses during the quadriceps fatigue test correlated with maximum oxygen consumption (r = 0.56, P < 0.05) and RPE at submaximal intensity (r = 0.84, P < 0.05) during cycling.
  
  
  CONCLUSIONS
  Greater impairment in muscle contractility is associated with enhanced perception of exertion and reduced maximal exercise capacity in FMS patients. Neuromuscular impairments should be considered as an important factor underlying functional limitations in FMS patients.
authors.affiliation: Université Joseph Fourier, Laboratoire HP2, and INSERM Unité 1042, Grenoble, France.
authors.forename: Damien
authors.initials: D
authors.lastname: Bachasson
authors.forename: Michel
authors.initials: M
authors.lastname: Guinot
authors.forename: Bernard
authors.initials: B
authors.lastname: Wuyam
authors.forename: Anne
authors.initials: A
authors.lastname: Favre-Juvin
authors.forename: Guillaume Y
authors.initials: GY
authors.lastname: Millet
authors.forename: Patrick
authors.initials: P
authors.lastname: Levy
authors.forename: Samuel
authors.initials: S
authors.lastname: Verges
mesh_terms: D000328:Adult; D004576:Electromyography / Q000379:methods; D005080:Exercise Test / Q000379:methods; D005260:Female; D005356:Fibromyalgia / Q000175:diagnosis / Q000503:physiopathology*; D006801:Humans; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology*; D052097:Quadriceps Muscle / Q000502:physiology*; D011795:Surveys and Questionnaires; D013577:Syndrome