Influence of gait-synchronized functional electrical stimulation during exoskeleton-assisted ambulation on cardiorespiratory outcomes in individuals with incomplete spinal cord injury

OBJECTIVE: To evaluate the impact of gait-synchronized functional electrical stimulation during exoskeleton-assisted ambulation on cardiorespiratory demand in individuals with incomplete spinal cord injury. DESIGN: Cross-sectional study employing a randomized crossover arrangement of measurements. PARTICIPANTS: Convenience sample of 11 individuals with chronic incomplete spinal cord injury and partial walking ability. METHODS: Participants completed 2 x 6-min walking tests (6MWTs) with the EksoNR, 1 with and 1 with-out gait-synchronized functional electrical stimulation targeting gait-related muscles in a randomized order. Cardiorespiratory and metabolic parameters were measured breath-by-breath via ergospirometry. The primary outcome was oxygen consumption (V̇O2/kg). Secondary outcomes included further cardiovascular and metabolic parameters. Data from the final 2 min of each 6MWT were analysed using linear mixed-effect models. RESULTS: V̇O2/kg increased by 6% with functional electrical stimulation compared with exoskeleton-assisted ambulation alone (15.07 ± 4.11 vs 14.21 ± 3.61 mL·min-¹·kg-¹, p = 0.02). Heart rate, ventilation, and energy expenditure were also elevated (p < 0.05), while breathing frequency, respiratory exchange ratio, distance, and perceived exertion remained unchanged. Inter-individual differences in V̇O2/kg were not explained by stimulation amplitude (r = 0.36, p = 0.27). CONCLUSION: Adding functional electrical stimulation to exoskeleton-assisted gait therapy consistently increased cardiorespiratory demand, potentially enhancing training intensity. Further research assessing long-term clinical impact is required.