Enhanced onset detection accuracy “reduces” the electromechanical delay of distal muscles

Measuring the electromechanical delay (EMD) in muscles requires onset detection of motor responses, which mostly is done by interactive cursor setting or by simple algorithms using amplitude thresholds. For best accuracy of experimental EMD results, highly sophisticated onset detection methods seem desirable which allow to discover smallest changes in the observed signal. Here, the authors demonstrates that upgrading the signal evaluation method can lead to “erroneous” results, if the performance of the experimental setup does not match that of the signal processing tool. Using high resolution data acquisition and evaluation methods, the authors found motor responses with a very small (or even negative) EMD in a distal (hand) muscle but these proved to originate from fast contractions of proximal (arm and shoulder) muscles. Their forces cannot be totally blocked by the wrist fixation due to the elastic skin tissue and, therefore, add to those of the slower hand muscle “reducing” their EMD artificially