title: Changes in the electromechanical delay components during a fatiguing stimulation in human skeletal muscle: an EMG, MMG and force combined approach.
abstract: OBJECTIVE
  Peripheral fatigue involves electrochemical and mechanical mechanisms. An electromyographic, mechanomyographic and force combined approach may permit a kinetic evaluation of the changes at the synaptic, skeletal muscle fiber, and muscle-tendon unit level during a fatiguing stimulation.
  
  
  METHODS
  Surface electromyogram, mechanomyogram, force and stimulation current were detected from the gastrocnemius medialis muscle in twenty male participants during a fatiguing stimulation (twelve blocks of 35 Hz stimulations, duty cycle 9 s on/1 s off, duration 120 s). The total electromechanical delay and its three components (between stimulation current and electromyogram, synaptic component; between electromyogram and mechanomyogram signal onset, muscle fiber electrochemical component, and between mechanomyogram and force signal onset, mechanical component) were calculated. Interday reliability and sensitivity were determined.
  
  
  RESULTS
  After fatigue, peak force decreased by 48% (P < 0.05) and the total electromechanical delay and its synaptic, electrochemical and mechanical components lengthened from 25.8 ± 0.9, 1.47 ± 0.04, 11.2 ± 0.6, and 13.1 ± 1.3 ms to 29.0 ± 1.6, 1.56 ± 0.05, 12.4 ± 0.9, and 17.2 ± 0.6 ms, respectively (P < 0.05). During fatigue, the total electromechanical delay and the mechanical component increased significantly after the 40th second, and then remained stable. The synaptic and electrochemical components lengthened significantly after the 20th and 30th second, respectively. Interday reliability was high to very high, with an adequate level of sensitivity.
  
  
  CONCLUSIONS
  The kinetic evaluation of the delays during the fatiguing stimulation highlighted different onsets and kinetics, with the events at synaptic level being the first to reveal a significant elongation, followed by those at the intra-fiber level. The mechanical events, which were the most affected by fatigue, were the last to lengthen.
authors.affiliation: Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy. emiliano.ce@unimi.it.
authors.forename: Emiliano
authors.identifier: http://orcid.org/0000-0003-0691-3153
authors.initials: E
authors.lastname: Cè
authors.affiliation: Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy.
authors.forename: Susanna
authors.initials: S
authors.lastname: Rampichini
authors.affiliation: Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Monti
authors.affiliation: Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Venturelli
authors.affiliation: Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy.
authors.forename: Eloisa
authors.initials: E
authors.lastname: Limonta
authors.affiliation: Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Esposito
mesh_terms: D000328:Adult; D006801:Humans; D008297:Male; D009119:Muscle Contraction; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D009213:Myography / Q000379:methods; D011930:Reaction Time; D009435:Synaptic Transmission
keywords: Electromyogram; Force; Latency; Mechanomyogram; Reliability; Skeletal muscle