Fig. 2

Stiffness modulation in the knee joint during gait. The expected human knee joint stiffness modulation during gait was estimated through an EMG-based model, which was verified in static (isometric) condition (adapted from [28]). A possible implementation of stiffness modulation could be to simplify this behavior into several regions with constant stiffness. The controller switches through these levels according to the gait phase. At the CYBATHLON 2016, we used a simpler strategy commanding a fixed stiffness setpoint. Nevertheless, the illustrated stiffness levels could be achieved in test bench experiments. Note that the gait cycle starts and ends with a heel strike of the same leg in this representation