Fig. 2

Impact of two different protocols of increasing contraction force on the sEMG signal and its PDF shape. In the example on the left panel, force was gradually increased from 0 to 20% MVC (a), whereas in the right panel force was increased in a step-wise fashion (d). The resulting sEMG signals are shown in plots b and e, and the corresponding filling factor values are shown in c and f. In plot b, the vertical arrows indicate the appearance of a few large-amplitude MUP spikes, clearly standing out from the previous sEMG activity. The onset of these prominent MUP spikes provoked an abrupt decrease in the filling factor (arrows in plot c). Note that the profile of the filling factor curve obtained when force was gradually increased (plot c) could not be accurately tracked when force was increased in constant-force steps (plot f)