Fig. 1.

Block diagram of the two-step optimization formulation. a_syn stands for activations reconstructed from synergy components, ma and ma_dev for moment arm and moment arm deviations, respectively, sa for activation scale factors for muscles with experimental EMG data, SV_mod for synergy vectors for muscles without experimental EMG data, $l_0^M$ and $s{l}_0^M$ for optimal fiber lengths and their scale factors, $l_s^T$ and $s{l}_s^T$ for tendon slack lengths and their scale factors, a for model activations, a_res for reserve activations, F_s for reserve actuator strength values (which are 0.5 Nm), a_thres for half-range of allowable activation variation (0.01 for muscles with associated experimental EMG data and 0.05 for all other muscles), f for muscle forces, and M for inverse dynamic moments. i is the muscle (44 muscles), j is the time frame (101 frames), and k is the tracked joint moment (six loads).