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