Are there mode-specific and fatigue-related electromechanical delay responses for maximal isokinetic and isometric muscle actions?

This study used a combined electromyographic, mechanomyographic, and force approach to identify electromechanical delay (EMD) from the onsets of the electromyographic to force signals (EMDE-F), onsets of the electromyographic to mechanomyogrpahic signals (EMDE-M), and onsets of mechanomyographic to force signals (EMDM-F). The purposes of the current study were to examine: (1) differences in EMDE-M, EMDM-F, and EMDE-F from the vastus lateralis between maximal isokinetic and maximal concentric isometric leg extensions; and (2) the effects of fatigue and recovery on EMDE-M, EMDM-F, and EMDE-F. These EMD measures were obtained from twelve men during maximal concentric isokinetic and isometric leg extensions pretest, posttest, and after 3-min and 5-min of recovery from 25 maximal isokinetic leg extensions at 60°s-1. The results indicated no differences between maximal isokinetic and isometric muscle actions for EMDE-M, EMDM-F, or EMDE-F during the pretest, posttest, 3-min recovery, and 5-min recovery measurements. These findings support the comparison of voluntary EMD measures between studies with different modes of exercise as long as the methodology for the determination of EMD are consistent. There were, however, fatigue-induced pretest to posttest increases in EMDE-M, EMDM-F, and EMDE-F which remained elongated after 3-min of recovery, but returned to pretest values after 5-min of recovery.