Individuals with neurological impairments often exhibit asymmetrical gait patterns. This study highlighted the potential of functional electrical stimulation (FES) to improve gait symmetry during treadmill training and investigated whether our proposed FES perturbation paradigm could induce gait adaptation concerning spatial and temporal gait symmetry in healthy subjects. In the FES perturbation paradigm, both legs received electrical pulses at the same period as the subjects’ initial stride duration, and the temporal gap between the two pulses for each leg was manipulated over 7 minutes. Following this, subjects continued to walk for another 5 minutes without FES. For the implicit trial (unconscious reaction to FES), subjects were asked to walk comfortably in response to the stimulation. For the explicit trial (conscious reaction to FES), subjects were asked to explicitly synchronize their toe-off phase to the stimulation. To examine the effects of the FES perturbation, we measured step length and stance time and then analyzed changes in step length and stance time symmetries alongside their subsequent aftereffects. In this study, regardless of whether subjects adapted their gait patterns to the electrical pulses explicitly or implicitly, a directional change was observed in stance time (temporal) symmetry under both conditions, with the right stance becoming longer than the left. The stance time asymmetry induced by FES perturbation resulted in a slight residual effect. No consistent trend of step length (spatial) symmetry changes was observed in either condition. This indicates that subjects may adapt their spatial gait patterns through diverse mechanisms. Our findings suggest that the applied FES perturbation strategy can induce adaptations in subjects’ temporal gait asymmetry, particularly while in stance. Further experiments would provide a deeper understanding of the mechanism behind subjects’ response to FES perturbations, as well as the long-term effects of these perturbations on the spatial and temporal aspects of gait symmetry.

All experiments were performed on a treadmill (Woodway USA, Waukesha, WI) equipped with supporting handrails to ensure the safety of subjects. All subjects were given an approximate 5-minute preparatory period to adjust to walking on the treadmill. Two motion-capturing markers were attached to the back of the subjects’ shoes and tracked by a camera-based motion-capturing system (Optotrak 3D Investigator, Norther Digital Inc. Canada). This system located the positions of the markers and sent the data to a PC in real time using a program developed with LabVIEW (National Instruments Corp., TX) to measure the subjects’ spatiotemporal gait parameters such as step length, stride period, and stance duration. In this study, the position of the most forward marker was designated as the heel strike position, while the most backward marker position was identified as the toe-off position. We determined the stride period by measuring the interval from one heel strike to the next, and the stance duration by measuring the interval from a heel strike to the subsequent toe-off. It is important to note that the actual instance of toe-off occurs slightly after the marker reaches its most backward position. Nonetheless, we adhered to these measurement criteria consistently, prioritizing the assessment of symmetry between the two legs.