title: Different recoveries of the first and second phases of the M-wave after intermittent maximal voluntary contractions.
abstract: OBJECTIVE
  We investigated the recovery of muscle electrical properties after intermittent intense exercise by examining separately the first and second phases of the muscle compound action potential (M-wave).
  
  
  METHODS
  M-waves and mechanical twitches were obtained using femoral nerve stimulation throughout the 30-min recovery period following 48 successive intermittent 3-s MVCs. The amplitude, duration, and area of the M-wave first and second phases, and the peak twitch force were measured from the knee extensors.
  
  
  RESULTS
  The amplitudes of both the first and second M-wave phases were increased immediately after exercise (P < 0.05), but, whereas the first phase remained enlarged for 5 min after exercise, the increase of the second phase only lasted for 10 s. After 30 min of recovery, the amplitude, area, and duration of both the first and second phases were decreased compared to control values (10-20%, P < 0.05). A significant temporal association was found between the changes in the amplitude and duration of the M-wave first phase (maximal cross correlations, 0.9-0.93; time lag, 0 s). A significant, negative temporal relation was found between the amplitude of the M-wave first phase and the peak twitch force during recovery (P < 0.05).
  
  
  CONCLUSIONS
  The prolonged enlargement of the M-wave first phase during recovery seems primarily related to fatigue-induced changes in membrane properties, whereas the extremely short recovery of the second phase might be related to changes in muscle architectural features. It is concluded that muscle excitability is impaired even after intermittent fatiguing contractions which allow partial clearance of extracellular K+.
authors.affiliation: Department of Electrical and Electronical Engineering, Public University of Navarra, Campus de Arrosadía s/n., 31006, Pamplona, Spain. javier.rodriguez.falces@gmail.com.
authors.forename: Javier
authors.initials: J
authors.lastname: Rodriguez-Falces
authors.affiliation: Institute of Sport Sciences, University of Lausanne, Lausanne, Switzerland.|Department of Physiology, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Place
mesh_terms: D000200:Action Potentials; D000328:Adult; D005267:Femoral Nerve / Q000502:physiology; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D018763:Muscle Fatigue; D052097:Quadriceps Muscle / Q000294:innervation / Q000502:physiology*
keywords: Fatigue; Femoral nerve stimulation; M-wave; Quadriceps; Recovery; Twitch