Neuromodulation with transcutaneous spinal stimulation reveals different groups of motor profiles during robot-guided stepping in humans with incomplete spinal cord injury

Exp Brain Res, 2023 · DOI: 10.1007/s00221-022-06521-5 · Published: February 1, 2023

Spinal Cord Injury Neurology Rehabilitation

Simple Explanation

This study investigates how transcutaneous spinal stimulation (TSS) affects robotic torques and EMG patterns during robot-guided stepping in individuals with incomplete spinal cord injury. Nine participants with chronic motor-incomplete SCI were studied during robot-guided stepping with TSS applied at random frequencies. The study found heterogeneous changes in robotic torques across individuals, identifying four groups with different patterns of changes depending on stimulation frequency and stance/swing phase.

Study Duration

Not specified

Participants

Nine chronic motor-incomplete SCI individuals (8/1 AIS-C/D, 8 men)

Evidence Level

Not specified

Key Findings

1
Agglomerative clustering of robotic torques identified four groups wherein the patterns of changes differed in magnitude and direction depending mainly on the stimulation frequency and stance/swing phase.
2
Changes in robotic torques were greater with increasing stimulation frequencies (four participants), which coincided with a decrease in EMG, mainly due to the reduction of clonogenic motor output in the lower leg muscles.
3
An inverted u-shape change in torque over the mid-frequency range along with an increase in EMG, reflecting the augmentation of gait-related physiological (two participants) or pathophysiological (one participant) output.

Research Summary

The study examined the immediate effect of continuous TSS across different stimulation frequencies on robotic torques in the hip and knee joints and muscle activation patterns in the lower limbs during treadmill stepping. Agglomerative clustering returned four groups that differed in the sign and magnitude of changes in robotic torques during stance and swing depending on the stimulation frequency. The study demonstrates different frequency and gait phase-dependent motor profiles during robot-guided stepping in humans with incomplete spinal cord injury.

Practical Implications

Personalized neuromodulation

The heterogeneous responses suggest the need for individualized TSS approaches based on patient-specific motor profiles.

Comprehensive assessment

The study highlights the value of using robotic torques and EMG during stepping to assess the effects of spinal stimulation.

Frequency-specific effects

Different stimulation frequencies can have distinct effects on motor output, requiring careful selection for therapeutic interventions.

Study Limitations

1
Walking continuously could produce fatigue, discomfort, and inconsistent engagement.
2
The stimulation intensity was not consistent across the participants due to discomfort.
3
It remains unknown, however, how our results relate to stimulation effects at specific frequencies over many more gait cycles.

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