Electromechanical delay during knee extensor contractions

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The purpose of this study was to investigate the magnitude of electromechanical delay (EMD) and its possible dependence on muscle type, type of contraction, fatigue, level of force, initial muscle length, and muscle contraction velocity. This was achieved using an experiment that measured voluntary knee extensor torques and surface EMG activity for a variety of different contractile conditions in seven male subjects. EMD values were obtained using a cross-correlation technique in three experimental KIN-COM dynamometer conditions of vastus medialis, rectus femoris, and vastus lateralis. In the first condition, a series of 10 repetitive submaximal (50% and 70% MVC) isometric knee extensor contractions were performed at knee angles of 90 degrees and 130 degrees extension. In the second condition, 10 maximal isokinetic knee extensor contractions were performed during passive shortening and lengthening. As such, the dynamometer was used to passively move the knee joint at 30 degrees.s-1 and 60 degrees.s-1. Both during lengthening and shortening, the contractions occurred at an angular position of 110 degrees. In the last condition, a repetitive submaximal isometric knee extensor fatigue test was performed for 100 s (150 contractions). At 10, 40, and 90 s during the time course of this fatigue test, a series of 10 contractions were recorded. To avoid a phase lag, which is introduced with one-way filtering, the EMG was processed with a bidirectional low-pass filter application. A significant main effect in EMD for the factor level of force was found. The EMD values obtained at a force level of 50% MVC were longer than at 70% MVC (107 vs 98 ms).(ABSTRACT TRUNCATED AT 250 WORDS)