Effects of Fatigue on Voluntary Electromechanical and Relaxation Electromechanical Delay

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 (E-F) ), the onsets of the electromyographic to mechanomyographic signals (EMD (E-M) ), the onsets of the mechanomyographic signal to force production (EMD (M-F) ), as well as the cessations of the electromyographic to force production (R-EMD (E-F) ), cessation of the electromyographic to mechanomyographic signals (R-EMD (E-M) ), and cessations of the mechanomyographic signal to force production (R-EMD (M-F) ); and 2) the relative contributions from EMD (E-M) and EMD (M-F) to EMD (E-F) as well as R-EMD (E-M) and R-EMD (M-F) to R-EMD (E-F) from the vastus lateralis in non-fatigued and fatigued states. The values EMD (E-F) , EMD (E-M) , EMD (M-F) , R-EMD (E-F) , R-EMD (E-M) and R-EMD (M-F) 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 (E-F) (73%;p<0.01), EMD (E-M) (99%;p<0.01), EMD (M-F) (60%;p<0.01), R-EMD (E-F) (101%;p<0.01) and R-EMD (M-F) (368%;p<0.01) (,) but no significant change in R-EMD (E-M) (25%;p=0.46). Fatigue-induced increase in EMD (E-F) indicated excitation-contraction coupling failure (EMD (E-M) ) and increases in the compliance of the series elastic component (EMD (M-F) ). Increases in R-EMD (E-F) were due to increases in relaxation time for the series elastic component (R-EMD (M-F) ), but not changes in the reversal of excitation-contraction coupling (R-EMD (E-M) ).