# INFLUENCE OF GAIT-SYNCHRONIZED FUNCTIONAL ELECTRICAL STIMULATION DURING EXOSKELETON-ASSISTED AMBULATION ON CARDIORESPIRATORY OUTCOMES IN INDIVIDUALS WITH INCOMPLETE SPINAL CORD INJURY

## TL;DR

Adding electrical muscle stimulation to a robotic exoskeleton during walking increases physical effort in people with spinal cord injuries, potentially improving rehabilitation outcomes.

## Contribution

This study is the first to show that gait-synchronized functional electrical stimulation during exoskeleton-assisted walking increases cardiorespiratory demand in individuals with incomplete spinal cord injury.

## Key findings

- Functional electrical stimulation increased oxygen consumption by 6% during exoskeleton-assisted walking.
- Heart rate and ventilation increased with stimulation, indicating higher workout intensity.
- Breathing frequency and perceived exertion remained unchanged despite increased effort.

## Abstract

To evaluate the impact of gait-synchronized functional electrical stimulation during exoskeleton-assisted ambulation on cardiorespiratory demand in individuals with incomplete spinal cord injury.

Cross-sectional study employing a randomized crossover arrangement of measurements.

Convenience sample of 11 individuals with chronic incomplete spinal cord injury and partial walking ability.

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.

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).

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.

People with incomplete spinal cord injury often experience reduced mobility and fitness. This study tested whether using functional electrical muscle stimulation while walking in a robotic exoskeleton would increase physical effort compared with walking with the exoskeleton without stimulation. Therefore, 11 participants walked with and without muscle stimulation using the exoskeleton. The results show that adding functional electrical stimulation while walking with a robotic exoskeleton significantly increased the amount of oxygen consumed by the body, indicating higher muscle activity. On average, oxygen consumption was increased by 6%. Heart rate and breathing also showed increases, suggesting a more intense workout. These findings are important because activating muscles more during rehabilitation may enhance gait function, weight management, and overall health in people with incomplete spinal cord injury. Our results support the use of exoskeleton therapy in combination with electrical muscle stimulation, but further research needs to evaluate the long-term impact.