Effects of intensity on muscle-specific voluntary electromechanical delay and relaxation electromechanical delay

The purposes of this study were to examine: 1) the potential muscle-specific differences in voluntary electromechanical delay (EMD) and relaxation electromechanical delay (R-EMD), and 2) the effects of intensity on EMD and R-EMD during step incremental isometric muscle actions from 10 to 100% maximal voluntary isometric contraction (MVIC). EMD and R-EMD measures were calculated from the simultaneous assessments of electromyography, mechanomyography, and force production from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) during step isometric muscle actions. There were no differences between the VL, VM, and RF for the voluntary EMD_E-M (onsets of the electromyographic to mechanomyographic signals), EMD_M-F (onsets the mechanomyographic to force production), or EMD_E-F (onsets of the electromyographic signal to force production) as well as R-EMD_E-M (cessation of electromyographic to mechanomyographic signal), R-EMD_M-F (cessation of mechanomyographic signal to force cessation), or R-EMD_E-F (cessation of electromyorgraphic signal to force cessation) at any intensity. There were decreases in all EMD and R-EMD measures with increases in intensity. 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 remained similar across all intensities. The superficial muscles of the quadriceps femoris shared similar EMD and R-EMD measurements.