Electromechanical delay: An experimental artifact.

The time delay between the onset of muscle activation and the onset of force or motion is commonly referred to as electromechanical delay, motor time, or motor execution time. This time has been used in the study of reaction time, of physiological properties of muscle, and of population differences. In this study, we show that electromechanical delay is comprised of two components. The first is transport time (t(t)) which is very brief (perhaps 10 ms). The second is the time to generate detectable changes in force (t(f)). The absolute duration of electromechanical delay is usually dominated by the second component which is influenced by four separate factors that are related in the following way: [Formula: see text] That is, t(f) is a function (g) of the product of two ratios. One is between the threshold T of the measuring device and the rate R at which muscle force rises. The other is the ratio of the mechanical impedances of the measuring device (Z(d)) and the muscle (Z(m)). We conclude that the measured absolute value of electromechanical delay has no physiological or psychological meaning and that task and performance induced changes need great care in their interpretation.