Meeting Abstract
P2-155 - Investigating the functions of human tibialis anterior during walking using a novel ‘muscle avatar’ technique Huck, TG*; Maharaj, J; Nishikawa, KC; Northern Arizona University, Flagstaff, AZ; Griffith University, Queensland, AUS; Northern Arizona University, Flagstaff, AZ tgh37@nau.edu
Muscles form a critical link in the control and mechanics of animal movement. Depending on subtle shifts in muscle length and phase of activation, muscles modulate limb-substrate interactions by adjusting among various roles—acting as motors, struts, springs, and brakes. Here, we investigated the varied mechanical behavior of the human tibialis anterior (TA) during level walking using a novel ‘muscle avatar’ approach. In vivo TA fascicle length (FL) and electromyography (EMG) data, both showing biphasic behavior, were taken from a single stride and streamed as length and activation inputs into ex vivo mouse extensor digitorum longus muscle preparations. Length inputs were scaled to accommodate a 10% length excursion around L0 at the in vivo frequency, while activation inputs consisted of trains of submaximal 45mV square wave pulses at 90Hz spanning the individual phases of the biphasic EMG signal (First and Second), and both phases combined (Full). For the First activation condition, stimulated during early- to mid-swing when the ankle dorsiflexes to achieve minimum toe clearance, the vast majority of work performed was positive (TA acted as a motor). During the Second activation condition, stimulated from late-swing through early-stance when the ankle plantarflexes to prepare for heel-strike as well as prevent foot-slap, nearly all work performed was negative (TA acted as a brake). Finally, for Full activation condition, work was split between positive and negative, with negative work depressed compared to the Second condition. The decrease in negative work in the Full condition suggests an effect of force depression from prior active shortening. Therefore, the biphasic activation of the TA apparently serves to amplify negative work at the beginning of stance by minimizing force depression during swing.