Biomechanical Effects of Varying Transcutaneous Spinal Cord Stimulation Amplitude During Walking in Individuals With Spinal Cord Injury: A Case Series

Transcutaneous spinal cord stimulation (tSCS) is a promising neuromodulation strategy with the potential to enhance locomotor rehabilitation for individuals with spinal cord injury. To maximize the effectiveness of this technique, it is crucial to select the optimal stimulation amplitude during a rehabilitation session. However, current tuning methods are time-consuming and subjective, relying on trial-and-error, clinician observations, and participant feedback. To improve this process, there is a need to define quantitative relationships between stimulation amplitude and measurable biomechanical metrics. In this study, we present a case series that includes two participants with motor-incomplete spinal cord injury walking with tSCS programmed to provide different stimulation amplitudes. We measured spatiotemporal parameters, electromyography, and inverse kinematics during overground walking with tSCS. Our results indicate that gait speed, stride length, and electromyography outcomes (e.g., muscle coactivation) systematically change with stimulation amplitude. This research is valuable in advancing our understanding of how stimulation amplitude relates to walking biomechanics. In the future, this knowledge will be used to design real-time, adaptive tSCS tuning methods for use in rehabilitation.