title: Extra Forces induced by wide-pulse, high-frequency electrical stimulation: Occurrence, magnitude, variability and underlying mechanisms.
abstract: OBJECTIVE
  In contrast to conventional (CONV) neuromuscular electrical stimulation (NMES), the use of "wide-pulse, high-frequencies" (WPHF) can generate higher forces than expected by the direct activation of motor axons alone. We aimed at investigating the occurrence, magnitude, variability and underlying neuromuscular mechanisms of these "Extra Forces" (EF).
  
  
  METHODS
  Electrically-evoked isometric plantar flexion force was recorded in 42 healthy subjects. Additionally, twitch potentiation, H-reflex and M-wave responses were assessed in 13 participants. CONV (25Hz, 0.05ms) and WPHF (100Hz, 1ms) NMES consisted of five stimulation trains (20s on-90s off).
  
  
  RESULTS
  K-means clustering analysis disclosed a responder rate of almost 60%. Within this group of responders, force significantly increased from 4% to 16% of the maximal voluntary contraction force and H-reflexes were depressed after WPHF NMES. In contrast, non-responders showed neither EF nor H-reflex depression. Twitch potentiation and resting EMG data were similar between groups. Interestingly, a large inter- and intrasubject variability of EF was observed.
  
  
  CONCLUSIONS
  The responder percentage was overestimated in previous studies.
  
  
  CONCLUSIONS
  This study proposes a novel methodological framework for unraveling the neurophysiological mechanisms involved in EF and provides further evidence for a central contribution to EF in responders.
authors.affiliation: Aix Marseille Université, CNRS, CRMBM UMR 7339, 13385 Marseille, France.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Wegrzyk
authors.affiliation: Aix Marseille Université, CNRS, CRMBM UMR 7339, 13385 Marseille, France.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Fouré
authors.affiliation: Aix Marseille Université, CNRS, CRMBM UMR 7339, 13385 Marseille, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Vilmen
authors.affiliation: Aix Marseille Université, CNRS, Institut de Mathématiques, UMR 7373, 13288 Marseille, France.
authors.forename: Badih
authors.initials: B
authors.lastname: Ghattas
authors.affiliation: Neuromuscular Research Laboratory, Schulthess Clinic, Zurich, Switzerland.
authors.forename: Nicola A
authors.initials: NA
authors.lastname: Maffiuletti
authors.affiliation: Aix Marseille Université, CNRS, CRMBM UMR 7339, 13385 Marseille, France; APHM, Hôpital Sainte Marguerite, Service de Rhumatologie, 13009 Marseille, France.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Mattei
authors.affiliation: Institute of Sport Sciences and Department of Physiology, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Place
authors.affiliation: Aix Marseille Université, CNRS, CRMBM UMR 7339, 13385 Marseille, France.
authors.forename: David
authors.initials: D
authors.lastname: Bendahan
authors.affiliation: Aix Marseille Université, CNRS, CRMBM UMR 7339, 13385 Marseille, France. Electronic address: julien.gondin@univ-amu.fr.
authors.forename: Julien
authors.initials: J
authors.lastname: Gondin
mesh_terms: D000328:Adult; D016000:Cluster Analysis; D004558:Electric Stimulation / Q000379:methods*; D004576:Electromyography; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D016037:Single-Blind Method
keywords: EMG; Extra Forces; NMES; Responder; Triceps surae