Fig. 4

Average muscle activations for the “unmeasured” muscles (upper) and “measured” muscles (lower) across calibration trials, legs and subjects from “Params” optimization (blue solid lines), SynX-based optimizations (\(S{\text{yn}}X_{Unmeasured} + Params\): red solid lines and \(S{\text{yn}}X_{{_{Unmeasured} }}^{Params}\): yellow solid lines) and SO-based optimizations (\(S{\text{yn}}X_{{_{All} }}^{Generic}\): purple dashed lines, \(S{\text{yn}}X_{{_{All} }}^{Params}\): green dashed lines and \(SO_{{_{Unmeasured} }}^{Params}\):grey dashed lines). Data are reported for a complete gait cycle, where 0% indicates initial heel-strike and 100% indicates subsequent heel-strike. For measured muscles, the curves associated with \(S{\text{yn}}X_{{_{Unmeasured} }}^{Params}\) and \(SO_{{_{Unmeasured} }}^{Params}\) were underneath the curves associated with “Params” since the associated muscle activations were taken from the “Params” optimization rather than estimated