Fig. 3

Effect of exoskeleton assistance on muscle activity in steady-state walking. We observed a gradual decrease in soleus muscle activity during the 20 min adaptation. Compared to minimal impedance mode (gray), average soleus activity was 19% lower at the end of the adaptation period (A). The soleus activity was decreased during the full duration of the stance phase (B), which is the result of the plantarflexion assistance provided by the exoskeleton (C). The desired exoskeleton moment was applied with a RMSE of 2.02 Nm with mainly larger differences between desired and actual moment during the first part of the stance phase. A paired t-test was used to compare muscle activity between controllers. A contains data of all subjects with the dots representing the median muscle activity during 3 min of walking and the bars the averaged data across subjects. The time series in B and C are based on data of one representative subject