Human fascicle strain behavior during twitch using ultrafast ultrasound

There is recent experimental evidence that sarcomere strain behavior is highly heterogeneous across and between muscle structures. Hence, considering the hierarchical architecture of muscles, also the behavior of all acting muscle substructures is effected. However, typical investigations are limited to ex-vivo experiments or pose serious limitations for in-vivo studies. In this work, we investigate in-vivo length changes in human muscle fascicles by means of non-invasive ultrafast ultrasound. To this end, we employ a research ultrasound system and a linear array transducer to image, in plane-wave mode, medial gastrocnemius muscles during electrically-stimulated contractions. The ultrasound-based approach presented in this study allows to measure strain distributions within muscle fascicles during contractions, where the sub-fascicle structures exhibit heterogeneous behaviors.