Fig. 1

The methodological pipeline to identify voluntarily activated motor units (MUs) using ultrafast ultrasound. A The ultrasound probe is placed on the skin to record data from the muscle’s cross-section (transverse view). B The recorded B-mode images. C Calculating displacement velocity images. D Separating the velocity images into spatiotemporal components using instantaneous blind source separation (BSS) with a focus on spatial sparsity, where each component is associated with a time signal and a spatial image. A subset of the components is putative estimates of the (1) MU territory in the spatial maps and (2) a sequence of MU twitches (unfused tetanic signal) evoked by the spike trains. E The spike trains are estimated based on unfused tetani. Previously using a Haar wavelet method (HWM). In this study, we estimate the spikes trains in E using the unfused tetanic signals from D using convolutive blind source separation (CBSS) and compare the performance against another method, i.e. the Haar wavelet method (HWM)