The Effect Of Isometric Strength Training On Electromechanical Delay Of The Vastus Lateralis

Abstract

PURPOSE To assess the influence of eight weeks of isometric leg extension strength training on electromechanical delay (EMD) of the vastus lateralis. METHODS Electromyographic (EMG) and Mechanomyographic (MMG) signals were recorded on thirteen male subjects (19–29 yrs). Subjects were randomly placed into a control (CG) group (N = 7) or a training (TG) group (N = 6). EMG and MMG signals were recorded at three time points (wks 0, 4, and 8) during leg extension training performed at 60° of leg flexion. The TG performed two sets of unilateral isometric muscle actions at 80% of their maximal isometric peak torque (PT) with the non-dominant leg for the first two weeks. The TG then performed three sets of isometric muscle actions at 80% of their maximal isometric PT for the last six weeks. Training sessions were conducted three days a week and each set of isometric muscle actions included ten 6 s repetitions. The delay in time between the onset of EMG and MMG activity (EMG-MMG) and between the onset of MMG activity and torque production (MMG-torque) were recorded in both TG and CG. RESULTS Participation in eight weeks of isometric leg extension strength training had no influence on EMG-MMG delay or MMG-torque delay within the TG subjects (p > 0.05). No significant differences existed in EMG-MMG delay or MMG-torque delay between the TG and CG subjects (p > 0.05). CONCLUSION These data indicate that eight weeks of isometric training did not significantly influence delay times in EMG-MMG or MMG-torque production in the vastus lateralis. It could be possible that isometric training did not have a significant influence on factors associated with changes in EMD. These factors include action potential propagation, excitation-contraction coupling, and/or stretching of the series elastic components.