Effect of different training modes on ground reaction forces during robot assisted floor walking and stair climbing

The HapticWalker is a robotic walking simulator for neurological gait rehabilitation. The device is based on the end-effector principle, i.e. the patients' feet are fixed on two footplates, his trunk is secured via a suspension harness. The footplates (end-effectors) of the robot guide the feet of the patient on freely programmable trajectories. Currently two different training modes are provided for each foot trajectory on the HapticWalker. Firstly training trajectories based on real motion capture data can be used. Secondly the vertical center of mass (CoM) motion can be incorporated into the foot trajectory. The latter method leaves the absolute position of the CoM constant, while the relative movement between CoM and feet remains the same as in free walking. Thereby the vertical CoM motion can be actively supported by using a fixed passive suspension, any type of controlled body weight support will then be accomplished via force controlled footplates. To characterize the training on the machine in position controlled mode, muscle activities as well as ground reaction force data of healthy subjects were collected. This article presents preliminary results from the investigation of ground reaction force data of healthy subjects. Therefore data of 10 healthy subjects was used to compare HapticWalker training modes vs. free walking on level ground and upstairs without any assistive devices and the aforementioned two HapticWalker training modes against each other. Amplitude and timing of force peaks during heel strike, foot flat and push off in vertical ground reaction forces were used for the assessment. In spite of a footplate, which does not provide a separate metatarsal joint for relative motion between fore and hind foot, during heel strike and push off the known characteristic peaks at the beginning and the end of the stance phase can be clearly distinguished. Though compared to free walking a slower and premature rise and slower decline of ground reaction forces can be seen due to the stiff guidance of the feet in position controlled mode. No significant differences appeared between the two described HapticWalker training modes.