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Electromechanical Delay and Peripheral Fatigue: Partitioning the Contributors during Electrically Evoked Contractions
Author(s) -
Esposito Fabio,
Monti Elena,
Rampichini Susanna,
Limonta Eloisa,
Venturelli Massimo,
Cè Emiliano
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1245.21
Subject(s) - isometric exercise , contraction (grammar) , muscle contraction , peripheral , stimulation , medicine , biomedical engineering , physical medicine and rehabilitation , cardiology
Skeletal muscle contraction is a phenomenon involving several mechanisms that are electrochemical and mechanical in nature. The time lag between muscle electrical activation and the beginning of force production has been previously defined as the electromechanical delay. A novel electromyographic (EMG), mechanomyographic (MMG) and force (F) combined approach can provide the duration of the electrochemical and mechanical components of the total delay (Delay TOT ). Prior investigations evaluated the acute effects of a fatiguing protocol on Delay TOT . The aim of this study was to evaluate the time course of the changes in the different Delay TOT components during a fatiguing stimulation. To this purpose, EMG, MMG and F signals were detected on the medial gastrocnemius muscle in eighteen male participants (age: 25±3 yrs; body mass: 77±4 kg; stature: 1.81±0.06 m; mean±SD) during a fatiguing protocol (twelve continuous stimulations at 35 Hz, 9.5 s on/0.5 s off; total time: 120 s) under isometric condition. Stimulation current (Stim) and EMG, MMG and F signals were recorded during contraction. The total electromechanical delay during contraction (Delay TOT ) and its three components (between Stim and EMG: Δt Stim‐EMG, synaptic component; between EMG and MMG: Δt EMG‐MMG, electrochemical component; and between MMG and F: Δt MMG‐F, mechanical component) were calculated. Before fatigue Delay TOT was 22.3±0.9 ms. Δt Stim‐EMG, Δt EMG‐MMG and Δt MMG‐F relative contribution to Delay TOT was 6%, 48% and 46%, respectively. During fatigue, Delay TOT and Δt MMG‐F lengthened significantly in the first 40 s, then remaining stable, whereas Δt Stim‐EMG and Δt EMG‐MMG increased until the 10 th and 30 th s, respectively. At the end of the fatiguing protocol, F decreased by 44%. Delay TOT was 31.2±1.6 ms. Δt Stim‐EMG, Δt EMG‐MMG and Δt MMG‐F significantly changed their contribution to 5%, 43% and 53%, respectively. During a fatiguing stimulation, the present EMG, MMG and F combined approach unveiled a different effect of peripheral fatigue with time on the synaptic, electrochemical and mechanical components. Support or Funding Information The study has been funded by the Department of Biomedical Sciences for Health, University of Milan