Effects of Transspinal Stimulation on Gait Patterns and Stability in Healthy Adults

Transspinal (or transcutaneous spinal cord) stimulation affects the spinal locomotor networks and is used to improve walking ability in people with spinal cord injury. However, the effects of transspinal stimulation at different frequencies and intensities on intralimb and interlimb coordination and on spatiotemporal gait characteristics has never been systematically investigated before. We hypothesized that transspinal stimulation, regardless of frequency and intensity, promotes physiological step progression and joint movements. Ten healthy young adults undertook a 10-minute baseline walk with no transspinal stimulation at their self-selected comfortable speed on a motorized treadmill, followed by six randomized walking bouts (two intensities × three frequencies) of 10-minute duration each with transspinal stimulation. Stimulation was delivered over the T10-L1 spinal process with interconnected anodes placed bilaterally on the iliac crest at either 15, 30, or 50 Hz (1-ms pulse; 10 kHz carrier frequency) at sub-threshold or supra-threshold intensities. Kinematics data collected using reflective markers attached to participants and tracked using an eight-camera motion analysis system. Static trials were used to define a seven-segment mechanical model of lower limbs. EMG was recorded bilaterally from leg muscles (soleus, tibialis anterior, medial gastrocnemius, vastus medialis, biceps femoris, hip adductor gracilis, gluteus medius, peroneus longus) using surface electrodes and linear envelopes were derived from the recordings. The step length and step width time series were evaluated with detrended fluctuation analysis to identify changes in the temporal structure of gait variability, while the largest Lyapunov exponent was used to establish the extent to which transspinal stimulation affected the dynamic stability of joint movements over stride-to-stride during walking. Additionally, the continuous relative phase was analyzed to determine the impact of transspinal stimulation on interlimb and intralimb coordination. Linear mixed-effects models followed by a generalized linear hypothesis test for planned contrasts were used to compare transspinal stimulation groups with the control group. Transspinal stimulation promoted a greater dynamic stability compared to control walking, a more stable intralimb and interlimb coordination, and a more persistent step length variability-characteristics of healthy gait. These results support that transspinal stimulation is an important neuromodulatory strategy that directly affects spinal locomotor centers.

Oct 7, 2024 4:00 PM — 5:00 PM

Society for Neuroscience (SfN) 2024 Conference