Effects of Fatigue on Voluntary Electromechanical and Relaxation Electromechanical Delay

Abstract

The purposes of the present study were to examine: 1) the effects of fatigue on electromechanical delay from the onsets of the electromyographic signal to force production (EMD), the onsets of the electromyographic to mechanomyographic signals (EMD), the onsets of the mechanomyographic signal to force production (EMD), as well as the cessations of the electromyographic to force production (R-EMD), cessation of the electromyographic to mechanomyographic signals (R-EMD), and cessations of the mechanomyographic signal to force production (R-EMD); and 2) the relative contributions from EMD and EMD to EMD as well as R-EMD and R-EMD to R-EMD from the vastus lateralis in non-fatigued and fatigued states. The values EMD, EMD, EMD, R-EMD, R-EMD and R-EMD were calculated during maximal voluntary isometric contractions, before and after 70% 1-repetition maximum leg extensions to failure. There were significant pretest to posttest increases in EMD (73%;p<0.01), EMD (99%;p<0.01), EMD (60%;p<0.01), R-EMD (101%;p<0.01) and R-EMD (368%;p<0.01) but no significant change in R-EMD (25%;p=0.46). Fatigue-induced increase in EMD indicated excitation-contraction coupling failure (EMD) and increases in the compliance of the series elastic component (EMD). Increases in R-EMD were due to increases in relaxation time for the series elastic component (R-EMD), but not changes in the reversal of excitation-contraction coupling (R-EMD).