title: New insights into the potentiation of the first and second phases of the M-wave after voluntary contractions in the quadriceps muscle.
abstract: We investigated the mechanisms underlying the potentiation of the first and second phases of the compound action potential (M-wave) after conditioning contractions.
  
  
  
  M-waves were evoked in the knee extensors before and after isometric maximal voluntary contractions (MVCs) of 1 s, 3 s, 6 s, 10 s, 30 s, and 60 s. The amplitude, duration, and area of the M-wave first and second phases were measured during the 10-min period after each contraction.
  
  
  
  The magnitude of the M-wave first phase was enlarged only after MVCs of 30 s and 60 s, whereas the second phase increased after all MVCs, regardless of their duration. The enlargement of the first phase remained for longer than 2 min, whereas the potentiation of the second phase lasted only 20 s.
  
  
  
  Potentiation of the first phase is the result of fatigue-induced membrane changes, whereas enlargement of the second phase is probably related to shortening of muscle fascicles. Muscle Nerve 55: 35-45, 2017.
authors.affiliation: Department of Electrical and Electronical Engineering, Universidad Pública de Navarra D.I.E.E., Campus de Arrosadía s/n, 31006, Pamplona, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Rodriguez-Falces
authors.affiliation: Institute of Sport Sciences and Department of Physiology, University of Lausanne, Lausanne, Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Place
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001703:Biophysics; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D007717:Knee / Q000294:innervation; D008297:Male; D052097:Quadriceps Muscle / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult
keywords: M-wave potentiation; conduction velocity; electromyography; femoral nerve stimulation; muscle architecture; muscle excitability