(A-17) Gait symmetric adaptation to functional electrical stimulation during treadmill walking

Introduction:: Individuals with neurological impairments, such as those who have survived a stroke, Parkinson’s disease, or multiple sclerosis, often experience secondary effects, such as asymmetric walking patterns. Asymmetric gait patterns can be characterized by various factors, such as differences in step length, stance phase time, and double-limb support time between the left and right sides of the legs during walking. Current physical rehabilitation techniques often use a split-belt treadmill to alter gait patterns during training, and the perturbation-based gait training has been shown to have short-term corrective effects on gait asymmetry. Functional electrical stimulation (FES) can also be used as an alternative training intervention to modulate gait symmetry. However, there has been little research done on the use of FES as a perturbation method to induce gait symmetric adaptation. Therefore, our study aimed to investigate whether FES-induced perturbations could induce sizeable changes in spatiotemporal gait symmetry in healthy subjects. Here, we focused on changes in temporal gait symmetry, including stance phase, swing phase, and double-limb support phase percentage, through the FES-induced perturbation paradigm, in which healthy subjects adapted their gait patterns to FES periodically applied to their right and left legs while walking on a treadmill.

Materials and Methods:: 21 healthy subjects (21±2.8 years) participated in this study. All subjects walked on a treadmill while connected to an electrical stimulator (MOTIONSTIM) via two electrodes (one on the mid-calf, and the other to the lower ankle) on both legs. Subjects’ stride period was measured using an Optotrak system. Each subject completed two separate trials (implicit and explicit trials). Each 15-min trial comprised a 4-min baseline period, a 7-min perturbation period, and a 5-min post-perturbation period. During the baseline period, we measured the time duration (τ) between the left-toe-off and the following right-toe-off phases and the stride duration from each gait cycle. During the perturbation period, subjects walked with applied electrical stimulation (0.12-second duration, 200 µs biphasic pulses at 90 Hz, 25~30 mA intensity). For the FES-induced perturbation, we delivered electrical pulses at the same period of the initial stride duration, and the electrical pulses delivered to the right and left legs were offset by the ∆τ. The offset time was then gradually adjusted to -20, -40, -60, -80, and -100 ms from the initial τ. For the implicit trial (unconscious reaction to FES), subjects were asked to walk normally and comfortably through the entire trial without attempting to synchronize their gait to the stimulation. On the other hand, for the explicit trial (consciously entrain their gait to FES), subjects were asked to synchronize their toe-off phase to the stimulation explicitly.

Results, Conclusions, and Discussions:: The figure shows the mean changes in stance and swing phase symmetry ratios across different epochs for both explicit and implicit trials. The percentage changes in symmetry were computed by comparing them to the baseline period’s average symmetry. We observed an increase in stance phase symmetry and an inverse change in swing phase symmetry for the explicit trial. The asymmetric pattern induced by the perturbation led to residual aftereffects that persisted during the 5-min post perturbation period. The implicit trail showed a slight change in stance phase and swing phase symmetry. No significant changes in double limb support symmetry were observed.

This study demonstrated that FES-induced perturbation, which delivers periodic electrical stimulation periodically to both legs in a manipulated way, has the effect of driving subjects’ gait adaptation in temporal gait symmetry through a process called entrainment (synchronizes a subject’s gait phase to the stimulus period). Further experiments will provide more insights into the long-term effects of FES-induced perturbation on changes in the temporal aspects of gait symmetry.

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