Optimization of human walking for exoskeletal support

It is hypothesized that healthy humans can reduce their energy expenditure during walking by wearing an exoskeleton. Exoskeletons are often designed for mechanical efficiency at joint level. This approach disregards the energy savings mechanisms in the human leg like bi-articular muscles and tendons. We use the muscle-reflex model to simulate the experiments by Cain et al. with an ankle exoskeleton actuated by a pneumatic muscle that supports plantarflexion. The muscle-reflex model predicts muscle activations and metabolic rate. The reflex-control parameters of the model were optimized for walking with and without support from an exoskeleton. The simulated exoskeleton uses either the EMG signal from the soleus muscle (proportional myoelectric control), or a footswitch to trigger the actuation of the pneumatic muscle. Cain et al. did find an experimental reduction in soleus muscle activation of 41.4 percent for the proportional myoelectric control and 13.0 percent for the footswitch control, where the optimization outcomes of simulated walking predicted a reduction of 42.8 percent and 25.9 percent respectively.