Fig. 5

a Representative input neural excitations (\(\mu (t)\)) for the subtalar model’s tibialis posterior (TP) and peroneus longus (PL) muscles processed using measured sEMG from AMI-4’s (Additional file 4: Table S1) residuum for model parameter optimization. b Corresponding 1.4 Hz reference trajectory measured from AMI-4’s intact subtalar and optimized model output trajectory generated from input \(\mu (t)\). Positive and negative values of \(\theta _{IE}\) indicate inversion and eversion, respectively. c Optimized models’ coefficients of determination between reference and output trajectories average 0.851 ± 0.026 (mean ± 1 SD) for standard amputation subjects (\(n = 4\)) and 0.866 ± 0.044 for AMI amputation subjects (\(n = 5\)), indicating no significant difference in fit (unpaired t-test, \(P = 0.5569\))