Anticipation augments distal leg muscle neuromechanics before, during, and after treadmill-induced perturbations applied during walking

We investigated the effect of anticipation on the proactive and reactive neuromechanical responses of the distal leg muscles in 20 young adults to anticipated and unanticipated rapid anterior or posterior treadmill-induced balance perturbations applied during walking. We quantified local medial gastrocnemius (MG) and tibialis anterior (TA) neuromechanics using cine B-mode ultrasound and surface electromyography before, during, and after the perturbation. Our findings partially supported the hypothesis that anticipated perturbations would elicit greater proactive agonist muscle adjustments than unanticipated perturbations. Though, these adjustments were direction-dependent; MG showed greater activation in anticipation of accelerations while TA activation did not change in anticipation of decelerations. Our findings contradicted our second hypothesis that unanticipated perturbations would elicit larger reactive agonist muscle responses than anticipated perturbations. Anticipated perturbations elicited greater agonist muscle excitations with no changes in muscle fascicle kinematics during the perturbed and recovery strides, suggesting that anticipation allows for greater force responsiveness of distal leg muscles when disrupted by a perturbation. Our results may inform remote monitoring of stability and balance using portable measurement tools, such as EMG and ultrasound, to monitor muscle dynamics in real time and mitigate the risk of falls.