Extra Forces induced by wide-pulse, high-frequency electrical stimulation: Occurrence, magnitude, variability and underlying mechanisms

Jennifer Wegrzyk (1) , Alexandre A Fouré (1) , Christophe Vilmen (1) , Badih Ghattas (2) , Nicola A. Maffiuletti (3) , Jean-Pierre Mattei (4) , Nicolas Place (5) , David Bendahan (1) , Julien Gondin (1)

1 CRMBM - Centre de résonance magnétique biologique et médicale
2 I2M - Institut de Mathématiques de Marseille
3 Neuromuscular Research Laboratory [Schulthess Clinic]
4 Hôpitaux Sud - Rhumatologie [Sainte- Marguerite - APHM]
5 Institut des Sciences du Mouvement et de la Médecine du Sport

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 (25 Hz, 0.05 ms) and WPHF (100 Hz, 1 ms) NMES consisted of five stimulation trains (20 s on-90 s 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. Conclusion: The responder percentage was overestimated in previous studies. Significance: 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. (C) 2014 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

Keywords: NMES; Muscle Strength; Skeletal; Responder; plateau-like behavior; spinal-cord-injury; Adult; Cluster Analysis; crmbm; Electric Stimulation; Electromyography; EMG; Evoked Potentials; Extra Forces; Female; H-Reflex; Humans; Male; Muscle Contraction; Muscle; post-activation depression; human skeletal-muscle; catch-like property; soleus h-reflex; neuromuscular stimulation; triceps surae; m-waves; presynaptic inhibition; Single-Blind Method

Domains: Life Sciences [q-bio]; Bioengineering

Jennifer Wegrzyk, Alexandre A Fouré, Christophe Vilmen, Badih Ghattas, Nicola A. Maffiuletti, et al.. Extra Forces induced by wide-pulse, high-frequency electrical stimulation: Occurrence, magnitude, variability and underlying mechanisms. Clinical Neurophysiology, 2015, 126 (7), pp.1400--1412. ⟨10.1016/j.clinph.2014.10.001⟩. ⟨hal-01414344⟩