iStride(TM) Device Used for Stroke Rehabilitation

Hemiparesis and other impairments are a frequent and disabling consequence of stroke and can lead to asymmetric and inefficient walking patterns. Training on a split-belt treadmill, which has two separate treads driving each leg at a different speed, can correct gait asymmetries post-stroke. However, the effects of split-belt treadmill training only partially transfer to everyday walking over ground and extended training sessions are required to achieve long-lasting effects. Our previous studies suggest that the iStride device that has been developed in our laboratory can be used as an alternative gait training device for people with stroke. The iStride device mimics the actions of the split-belt treadmill, but can be used during over-ground walking and in one's own home, thus enabling long-term training. The iStride device does not require any external power and is completely passive; all necessary forces are redirected from the natural forces present during walking since it utilizes the wearer's weight to generate its movements. While the movements of the iStride device are similar to the split belt treadmill, and the iStride device generates a similar aftereffect, the efficacy of this shoe in modifying the gait of an individual with stroke is not yet verified.

In this study, we will test the efficacy of the iStride device on individuals with stroke in the clinic. Efficacy will be evaluated based on the change in gait coordination and also based on subjects' self-reported comfort on the device. We predict that the iStride device will result in changes to interlimb coordination of gait that could be a safe and effective device to be used in ones' home.

The asymmetric nature of hemiparetic gait can have a large impact on functional walking ability. For example, swing phase asymmetry is a significant predictor of hemiparetic walking performance because it strongly correlates with stages of motor recovery, walking speed, and falls. Another measure of temporal asymmetry - double support duration - is similarly correlated with walking speed. In addition, spatial (e.g. step length) asymmetry is associated with decreased propulsive force on the paretic leg, which limits forward motion of the body and reduces gait efficiency. The importance of gait efficiency should not be understated - the elevated energy demands of hemiparetic gait combined with physical deconditioning post-stroke can greatly limit performance of activities of daily living, contributing to poor cardiovascular fitness and metabolic syndrome. In turn, this can increase the risks of a second stroke or cardiovascular event and is associated with increased morbidity and mortality rates. Therefore, improving gait symmetry should be an important goal for therapy, to not only improve functional mobility and reduce injury, but also to enhance general health and well-being post-stroke.

Practicing walking on a split-belt treadmill can correct abnormal interlimb coordination of gait in individuals with hemiparesis following stroke or other central nervous system lesions. Asymmetric gait can manifest as a spatial asymmetry, in which steps taken on one side are longer than those on the other. It can also manifest as a temporal asymmetry, where the timing is uneven on the paretic and non-paretic sides. Temporal asymmetries are often measured as differences in the duration of double support periods, which are the amount of time both feet are simultaneously contacting the ground and are measured separately for the paretic and non-paretic sides. The iStride device is designed to cause changes in both spatial and temporal gait symmetry. We predict that the iStride device would cause the steps on the side with the iStride device to be larger since individuals would compensate for the backward rolling motion by placing their foot farther forward in stance, thus increasing the distance between the two feet. Similarly, since the stride is longer, it may also shorten the duration of stance relative to the other side. With shortened stance duration, the amount of time spent in double-support at the end of stance would likely decrease as well.

Although the original idea of the iStride device is derived from the motion of the split-belt-treadmill, there are distinct differences between walking on the device and walking on a split-belt treadmill with asymmetric belt velocities. While the body's velocity relative to ground is zero on a split-belt treadmill, the relative velocity of the iStride device is non-zero and forward. The device forces the wearer's foot forward or backward whereas the treadmill moves both feet backward, but at different speeds. For both the split-belt treadmill and the iStride device, the relative velocity between both feet is similar and the backward-moving iStride device takes the place of the faster tread.