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The History Dependence of the EMG‐Force Relationship during Ankle Dorsiflexion
Author(s) -
Paquin James,
Power Geoffrey A
Publication year - 2017
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.31.1_supplement.905.2
Subject(s) - isometric exercise , electromyography , ankle , medicine , contraction (grammar) , ankle dorsiflexion , muscle contraction , physical medicine and rehabilitation , cardiology , anatomy
The steady‐state isometric contraction following a shortening or lengthening muscle action shows distinctly different force and activation levels as compared with a purely isometric contraction at the same muscle length. This study investigated how prior active lengthening (residual force enhancement; RFE) and shortening (force depression; FD) influences the isometric electromyography (EMG)‐Force relationship at submaximal and maximal levels as compared with purely isometric (ISO) contractions. By utilizing a series of force clamps and activation clamps at 20%, 40%, 60%, 80% and 100% of maximal isometric voluntary contraction (MVC) and maximal isometric integrated EMG (iEMG), respectively, the relative differences in neuromuscular efficiency (e.g., force/iEMG) between ISO, RFE, and FD were investigated. 17 healthy young male subjects were seated on a cybex dynamometer and performed voluntary contractions of the ankle dorsiflexors. Subjects first performed an MVC to determine relative intensities, then performed randomized active lengthening and shortening contractions at 25 deg/s over a 25 deg excursion ending at 115 degs respectively. These contractions were then compared with the purely isometric contraction at 115 degs. Surface EMG was used to record from tibialis anterior and soleus. In the RFE state when compared to the ISO state, there was significantly higher torque production during 100% MVC (~7%, P<0.05) with no significant change in agonist iEMG. Submaximally, less agonist iEMG was required to achieve the same amount of force at 60% MVC (P<0.05), and approaching significance for 40% and 20% MVC (P=0.07 and P=0.06 respectively), indicative of increased neuromuscular efficiency. In the FD state compared to the ISO state it was found that there was significantly less force produced during MVC (~15%, P<0.0001) with no significant change in agonist iEMG, but an increase in antagonist iEMG (P<0.05). In the submaximal FD state there was more agonist iEMG required to achieve the same levels of force at 80%, 60%, 40%, and 20% MVC (P<0.05), accompanied by significant increases in antagonist iEMG at 60% and 40% MVC (P<0.05). From these results, it can be concluded that the history dependent states have independent EMG‐Force relationships that exhibit significantly different levels of neuromuscular efficiency than the isometric EMG‐Force relationship. Support or Funding Information NSERC ‐ Natural Science and Engineering Research Council of Canada