The Etiology of Muscle Fatigue Differs between Two Electrical Stimulation Protocols

Authors:
  • SGSidney Grosprêtre
    Sidney Grosprêtre
  • CVChristophe Vilmen
    Christophe Vilmen
  • MGMaxime Guye
    Maxime Guye
  • JMJean-Pierre Mattei
    Jean-Pierre Mattei
  • YFYann LE Fur
    Yann LE Fur
  • DBDavid Bendahan
    David Bendahan
  • JGJulien Gondin
    Julien Gondin
Publisher website
Google Scholar
Abstract
Purpose This study aimed at investigating the mechanisms involved in the force reduction induced by two electrical stimulation (ES) protocols that were designed to activate motor units differently. Methods The triceps surae of 11 healthy subjects (8 men; age, ~28 yr) was activated using ES applied over the tibial nerve. Two ES protocols (conventional [CONV]: 20 Hz, 0.05 ms vs wide-pulse high-frequency [WPHF]: 80 Hz, 1 ms) were performed and involved 40 trains (6 s on–6 s off) delivered at an intensity (IES) evoking 20% of maximal voluntary contraction. To analyze the mechanical properties of the motor units activated at IES, force–frequency relation was evoked before and after each protocol. H-reflex and M-wave responses evoked by the last stimulation pulse were also assessed during each ES protocol. Electromyographic responses (∑EMG) were recorded after each train to analyze the behavior of the motor units activated at IES. Metabolic variables, including relative concentrations of phosphocreatine and inorganic phosphate as well as intracellular pH, were assessed using 31P-MR spectroscopy during each protocol. Results Larger H-reflex amplitudes were observed during WPHF as compared with CONV, whereas opposite findings were observed for M-wave amplitudes. Despite this difference, both the force reduction (−26%) and metabolic changes were similar between the two protocols. The CONV protocol induced a rightward shift of the force–frequency relation, whereas a significant reduction of the ∑EMG evoked at IES was observed only for the WPHF. Conclusions These results suggest that a decreased number of active motor units mainly contributed to WPHF-induced force decrease, whereas intracellular processes were most likely involved in the force reduction occurring during CONV stimulation.

This publication has 35 references indexed in Scilit: