Muscle-Specific Neuromuscular Recruitment as a Candidate Mediator of Functional Recovery in Robot-Assisted Gait Training Combined with Transcutaneous Spinal Cord Stimulation: A Secondary Analysis in Incomplete Spinal Cord Injury
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Abstract
Background: Robot-assisted gait training combined with transcutaneous spinal cord stimulation may improve mobility after incomplete spinal cord injury, but the muscle-specific neuromuscular pattern underlying these effects remains uncertain. Objective: To examine whether muscle-specific intramuscular electromyographic recruitment and progressive body-weight-support reduction provided a plausible mechanistic explanation for the functional advantage of combined robotic gait training and spinal stimulation. Methods: This hypothesis-generating secondary analysis used data from a double-blind randomized trial of 20 adults with intermediate-phase incomplete spinal cord injury allocated to RAGT+tSCS (n=13) or CPT+tSCS (n=7). Participants completed 40 sessions over 8 weeks. Group × Time effects were examined for iEMG amplitudes of the gastrocnemius medialis, vastus lateralis, tibialis anterior, and biceps femoris and compared with functional outcomes. Associations between treatment assignment and body-weight-support requirement were evaluated using Pearson’s correlation. Results: Large interactions were observed for the gastrocnemius medialis (partial η²=0.924), vastus lateralis (η²=0.880), and tibialis anterior (η²=0.859), but not the biceps femoris (η²=0.061; p=0.293). Functional effects were largest for the Timed Up and Go test (η²=0.844) and Berg Balance Scale (η²=0.702), whereas the 10-Meter Walk Test showed no between-group interaction (η²=0.008; p=0.708). Treatment assignment correlated with body-weight-support requirement at sessions 1 (r=−0.886) and 20 (r=−0.867), both p<0.001. Conclusion: RAGT+tSCS was associated with selective recruitment of ankle and knee stabilizing muscles corresponding with balance and transitional-mobility gains. Progressive unloading represented a plausible candidate mechanism but was not formally established as a mediator
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