A Novel Elastic Force-Field to Influence Mediolateral Foot Placement During Walking.

Bipedal gait can be stabilized through mechanically-appropriate mediolateral foot placement, although this strategy is disrupted in a subset of neurologically injured individuals with balance deficits. The goal of the present work was to develop a device to influence mediolateral foot placement during treadmill walking. We created a novel force-field using a combination of passive elasticity and active control; wires in series with extension springs run parallel to the treadmill belts and can be rapidly repositioned to exert mediolateral forces on the legs of users. This mechanical structure creates a channel-like force landscape that resists displacements of each leg away from its prescribed mediolateral position, producing near-linear effective mediolateral stiffness. The depth of these force-field channels can be predictably controlled by manipulating extension spring initial tension. In human testing, we found that the force-field can effectively "get-out-of-the-way" when desired, closely following the mediolateral leg trajectory with a delay of approximately 110 ms. The force-field can also encourage users to adjust their mediolateral foot placement in order to walk with either narrower or wider steps, without interfering with forward gait progression. Future work will test whether this novel device can help retrain a stable gait pattern in clinical populations.