Fig. 1
Setup and signal flow in the pNMS29. The multi-body simulation has nine degrees of freedom. Revolute joints in the hips, knees, and ankles connect the trunk, femur, tibia, and foot. Based on joint angles \(\varphi\) and angular velocities \(\dot{\varphi }\), the muscle model calculates the current length and force for each of the seven muscles per leg. A neural feedback controller computes the individual muscle stimulations \(S_m\) based on the current muscle length \(l_\text {ce}\), the MTU force \(F_\text {MTU}\), the head-arm-trunk segment (HAT) angle and angular velocity \(\varphi _\text {HAT}\) and \(\dot{\varphi }_\text {HAT}\), the ground contact of heel and ball \(c_\text {h,b}\), and the body load on the left and right leg \(F_\text {l,r leg}\). The muscle-tendon forces resulting from the given muscle stimulation and the passive, elastic tendon properties are multiplied by their respective lever arms and summed for all muscles. The total joint torques T are fed back into the multi-body simulation. We focus on the VAS, GAS, and HAM and deactivate them for defined periods.
