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.

We hypothesize that training over ground will lead to a change in the interlimb coordination in individuals with asymmetric gait and allow individuals to develop a more persistent symmetric gait. There are several differences between training on ground and a treadmill, such as visual flow and vestibular information signaling forward movement that likely limit the expression of learning in the over-ground context when trained on a treadmill. Visual cues appear to be particularly important for context awareness. Visual cues, coupled with prior experience, are so powerful that predictive postural responses cause an individual to stumble when stepping onto an escalator that is not moving. The body has learned an internal model that expects an acceleration when stepping onto an escalator, but when that acceleration does not occur, the person stumbles. A study of split-belt walking showed that transfer to over-ground walking is enhanced when subjects are blindfolded during training on the treadmill and tested over ground. Since blindfolding eliminates visual cues about the environment, this also suggests that vision is a key factor in determining the context-dependence of learning. Since it is not realistic to blindfold stroke patients during gait training, we designed the iStride device so that training could occur during over-ground walking, thus visual cues during training and later walking over ground would be the same.

Data from control subjects using an earlier version of the iStride device (referred to as GEMS at the time) has been published and a video of this previous version can be found at http://reedlab.eng.usf.edu/publications/handzic2011GEMS.mp4. In this study, we found that this earlier version of the device was capable of changing step length as predicted, however the previous design was too heavy and too tall to be considered practical for testing in stroke populations. The current version of the iStride device produces similar motion to the previous version, but it weighs less (under 1 kg) and is shorter (~4.4 cm). We will test the efficacy of wearing the current iStride device on gait coordination during walking over ground on individuals with stroke in the clinic. All walking will be performed while subjects are closely guarded by an experienced physical therapist to prevent falling. The effects of the iStride device on gait coordination will be compared to those induced on a split-belt treadmill.

The proposed project represents one of the first attempts to build a device that corrects walking symmetry while walking over ground. Not only would this allow people to experience gait corrections while performing normal movements, but the simplicity and relative low cost of these devices would also open up potential opportunities to train at home (for high-functioning individuals with supervision) and in clinics where a split-belt treadmill is not available. The studies outlined here will establish whether the iStride device is capable of changing interlimb coordination of gait, and whether individuals with stroke can use these devices for rehabilitation purposes. This work will thus build the foundation for future training studies examining the effectiveness of long-term use of the iStride device for improving symmetric walking patterns.

The question that this study targets is the modification of human walking patterns for use in stroke rehabilitation. It is our ultimate objective to show that the iStride device can change a person's temporal and spatial gait asymmetry into a symmetric gait. Our points of reference are results obtained by previous studies with split-belt treadmills. We are also interested in how altering the interface between a foot and the ground influences the adaptation to new walking patterns.