Mean and standard deviation of d1 and d2 values for AD across the 5 trials of experiment I. tEMG was automatically calculated with the single-threshold algorithm described in section III with parameters M = 100, and P = 120. Note the different behavior of the muscle across different subjects. Negative values indicate that the EMG onset occurs before the instant that υ exceeds the speed threshold. positive values, especially if high suggest that muscle action was not related to movement; other muscles, either external (e.g., trunk muscles) or internal to the subset recorded for the subject, could have generated the movement (see text)