Figure 3. Normalization of swing phase kinematics in the presence of perturbations.
A, application of vertical force fields on the hindlimb during one step cycle in a complete spinal rat. Robot arms were attached to the shank of the hindlimb during bipedal hindlimb stepping. The robot arms apply an upward force on the shank when the hindlimb moves forward during the swing phase of the step cycle. The magnitude of the force (arrows) is proportional to the horizontal velocity of the hindlimb. B, adaptations to the vertical force fields occur during stepping. In each trial (1-5), spinal rats were repeatedly exposed to the force field for 25 steps, followed by 25 steps without the force field. Swing duration (time from toe off (TO) to paw contact (PC)) and hindlimb coordination (interlimb TO-PC interval) were analysed and the data from 25 steps were averaged. Values are means ±s.e.m. for each trial (25 steps) from one spinal rat stepping at a treadmill speed of 11 cm s−1. (Authors' unpublished observations.)