title: Neuromuscular fatigue is not different between constant and variable frequency stimulation.
abstract: This study compared fatigue development of the triceps surae induced by two electrical stimulation protocols composed of constant and variable frequency trains (CFTs, VFTs, 450 trains, 30 Hz, 167 ms ON, 500 ms OFF and 146 ms ON, 500 ms OFF respectively). For the VFTs protocol a doublet (100 Hz) was used at the beginning of each train. The intensity used evoked 30% of a maximal voluntary contraction (MVC) and was defined using CFTs. Neuromuscular tests were performed before and after each protocol. Changes in excitation-contraction coupling were assessed by analysing the M-wave [at rest (Mmax) and during MVC (Msup)] and associated peak twitch (Pt). H-reflex [at rest (Hmax) and during MVC (Hsup)] and the motor evoked potential (MEP) during MVC were studied to assess spinal and corticospinal excitability of the soleus muscle. MVC decrease was similar between the protocols (-8%, P<0.05). Mmax, Msup and Pt decreased after both protocols (P<0.01). Hmax/Mmax was decreased (P<0.05), whereas Hsup/Msup and MEP/Msup remained unchanged after both protocols. The results indicate that CFTs and VFTs gave rise to equivalent neuromuscular fatigue. This fatigue resulted from alterations taking place at the muscular level. The finding that cortical and spinal excitability remained unchanged during MVC indicates that spinal and/or supraspinal mechanisms were activated to compensate for the loss of spinal excitability at rest.
authors.affiliation: Aix-Marseille University, CNRS, ISM UMR 7287, Marseille, France ; Movement to Health Laboratory, Euromov, Montpellier 1 University, Montpellier, France.
authors.forename: Maria
authors.initials: M
authors.lastname: Papaiordanidou
authors.affiliation: Movement to Health Laboratory, Euromov, Montpellier 1 University, Montpellier, France ; GRAME, Faculté de Médecine, Département de Kinésiologie, Université Laval, Québec, Canada.
authors.forename: Maxime
authors.initials: M
authors.lastname: Billot
authors.affiliation: Movement to Health Laboratory, Euromov, Montpellier 1 University, Montpellier, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Varray
authors.affiliation: INSERM U1093 Cognition, Action et Plasticité Sensorimotrice, Université de Bourgogne, UFR STAPS, Dijon, France.
authors.forename: Alain
authors.initials: A
authors.lastname: Martin
mesh_terms: D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D018763:Muscle Fatigue / Q000502:physiology*