title: The effect of muscle fatigue on stimulus intensity requirements for central and peripheral fatigue quantification.
abstract: OBJECTIVE
  The present study was designed to determine the stimulation intensity necessary for an adequate assessment of central and peripheral components of neuromuscular fatigue of the knee extensors.
  
  
  METHODS
  Three different stimulation intensities (100, 120 and 150% of the lowest intensity evoking a plateau in M-waves and twitch amplitudes, optimal stimulation intensity, OSI) were used to assess voluntary activation level (VAL) as well as M-wave, twitch and doublet amplitudes before, during and after an incremental isometric exercise performed by 14 (8 men) healthy and physically active volunteers. A visual analog scale was used to evaluate the associated discomfort.
  
  
  RESULTS
  There was no difference (p > 0.05) in VAL between the three intensities before and after exercise. However, we found that stimulating at 100% OSI may overestimate the extent of peripheral fatigue during exercise, whereas 150% OSI stimulations led to greater discomfort associated with doublet stimulations as well as to an increased antagonist co-activation compared to 100% OSI.
  
  
  CONCLUSIONS
  We recommend using 120% OSI, as it constitutes a good trade-off between discomfort and reliable measurements.
authors.affiliation: Institute of Movement Sciences and Sports Medicine, University of Geneva, Geneva, Switzerland.
authors.forename: Daria
authors.initials: D
authors.lastname: Neyroud
authors.forename: Alexia
authors.initials: A
authors.lastname: Vallotton
authors.forename: Guillaume Y
authors.initials: GY
authors.lastname: Millet
authors.forename: Bengt
authors.initials: B
authors.lastname: Kayser
authors.forename: Nicolas
authors.initials: N
authors.lastname: Place
mesh_terms: D000328:Adult; D004558:Electric Stimulation; D015444:Exercise; D005260:Female; D006801:Humans; D007537:Isometric Contraction; D007717:Knee / Q000294:innervation / Q000502:physiology; D008297:Male; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*