Selective neural stimulation methods improve cycling exercise performance after spinal cord injury: a case series

Kristen Gelenitis,Ronald Triolo,Lisa Lombardo,Kevin Foglyano

doi:10.1186/s12984-021-00912-5

Abstract

BackgroundExercise after paralysis can help prevent secondary health complications, but achieving adequate exercise volumes and intensities is difficult with loss of motor control. Existing electrical stimulation-driven cycling systems involve the paralyzed musculature but result in rapid force decline and muscle fatigue, limiting their effectiveness. This study explores the effects of selective stimulation patterns delivered through multi-contact nerve cuff electrodes on functional exercise output, with the goal of increasing work performed and power maintained within each bout of exercise.MethodsThree people with spinal cord injury and implanted stimulation systems performed cycling trials using conventional (S-Max), low overlap (S-Low), low duty cycle (C-Max), and/or combined low overlap and low duty cycle (C-Low) stimulation patterns. Outcome measures include total work (W), end power (Pend), power fluctuation indices (PFI), charge accumulation (Q), and efficiency (η). Mann–Whitney tests were used for statistical comparisons of W and Pend between a selective pattern and S-Max. Welch’s ANOVAs were used to evaluate differences in PFIs among all patterns tested within a participant (n ≥ 90 per stimulation condition).ResultsAt least one selective pattern significantly (p < 0.05) increased W and Pend over S-Max in each participant. All selective patterns also reduced Q and increased η compared with S-Max for all participants. C-Max significantly (p < 0.01) increased PFI, indicating a decrease in ride smoothness with low duty cycle patterns.ConclusionsSelective stimulation patterns can increase work performed and power sustained by paralyzed muscles prior to fatigue with increased stimulation efficiency. While still effective, low duty cycle patterns can cause inconsistent power outputs each pedal stroke, but this can be managed by utilizing optimized stimulation levels. Increasing work and sustained power each exercise session has the potential to ultimately improve the physiological benefits of stimulation-driven exercise.

Highlights

Exercise after paralysis can help prevent secondary health complications, but achieving adequate exercise volumes and intensities is difficult with loss of motor control
Though differences exist among participants and patterns, a general discussion for trends in each outcome measure and their implications is first presented : Total work S-Low and Carousel with Maximum Overlap (C-Max) 2c paradigms significantly increased total work performed over conventional (S-Max) stimulation, effectively enabling a more intense workout within the same amount of time
Results of this study show that low fiber overlap and low duty cycle stimulation paradigms can significantly increase work performed during an exercise session over conventional stimulation, and often have potential for further improvement with extended cycling durations, supporting our initial hypothesis

Summary

Introduction

Exercise after paralysis can help prevent secondary health complications, but achieving adequate exercise volumes and intensities is difficult with loss of motor control. Existing electrical stimulation-driven cycling systems involve the paralyzed musculature but result in rapid force decline and muscle fatigue, limiting their effectiveness. Upper motor neuron paralysis resulting from spinal cord injury (SCI) and other neuromuscular disorders leads to numerous secondary health complications. People with lower extremity paralysis have historically been restricted to exercising with only the upper body muscles for which they maintain control. Hand-cycling and arm weight exercises maintain upper body tone and provide some cardiovascular workout, but do not address the complications specific to the paralyzed lower extremities. Electrical stimulation-driven exercise systems provide a more complete, full-body workout by engaging the paralyzed musculature [5, 6]. Several studies have shown marked improvements in lower extremity muscle mass [8], body composition [9], and perceived quality of life [10] after participants with SCI train with these systems

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