Reaction times and electromechanical delay in reactions of increasing and decreasing force

The purpose of this study was to compare reaction times and electromechanical delay between reactions to increase force from rest and reactions to decrease force from an active state in the quadriceps femoris of healthy young adults. Force, position, and electromyographic data were recorded from 35 subjects reacting to a forced knee-flexion perturbation. Electromechanical delay was assessed through cross-correlation of the filtered EMG and force data. Reaction time to increase force (M = 159.9 msec., 95 % CI = 149.9-169.9 msec.) was significantly longer than RT to decrease force (M = 124.4 msec., 95% CI = 118.7-130.1 msec.). This difference was partially caused by a difference in electromechanical delay (RT to increase force electromechanical delay was 63 msec., 95% CI = 60-67 msec., greater than the RT to decrease force electromechanical delay of 49 msec., 95% CI = 46-52 msec.). This difference in reaction time could be important in identifying and interpreting physiologically meaningful changes in muscle force and in intermuscular coordination during movement.