Fig. 1

Experimental setup and single-subject perturbation profiles. a Schematic overview of the experimental setup. In the schematic the left leg is the stance leg. For the right stance leg the leftward and rightward arrow colors interchange. b Reference (dashed) and measured (solid) interaction force between motor and subject. c Reference (dashed) and measured (solid) motor impulse, obtained by integrating the interaction forces. d ML COM velocity relative to the walking surface. e EMG profile of the swing leg gluteus medius. Colors indicate the various perturbations. Lines represent within-subject averages of a single subject. Shaded areas indicate the within-subject standard deviation. The subject shown was the subject with the highest step frequency among subjects. The square on the time axis indicates the average time of heel strike after perturbation onset at toe-off (paretic and non-paretic pooled)