Testing a Novel Wearable Device for Motor Recovery of the Elbow Extensor Triceps Brachii in Chronic Spinal Cord Injury

eNeuro, 2023 · DOI: https://doi.org/10.1523/ENEURO.0077-23.2023 · Published: July 17, 2023

Spinal Cord Injury Neurology Neuroplasticity

Simple Explanation

This study investigates a wearable device that pairs auditory clicks with electrical stimulation to improve triceps muscle function in individuals with spinal cord injury (SCI). The device aims to strengthen connections to the triceps muscle, similar to previous success with the biceps muscle. Healthy volunteers and chronic SCI survivors used the device, but surprisingly, the study found no significant improvement in triceps muscle function or electrophysiological measurements. The results suggest that the triceps muscle might be less responsive to this type of stimulation compared to the biceps, which could explain the difficulty in recovering triceps function after spinal cord injury.

Study Duration

4 weeks

Participants

11 healthy volunteers, 22 chronic cervical SCI survivors

Evidence Level

Level II; Randomized Crossover Trial

Key Findings

1
Paired stimulation did not increase the StartReact effect in healthy volunteers, indicating no enhancement of reticulospinal tract activity.
2
The wearable device did not decrease the suppression of responses to transcranial magnetic brain stimulation (TMS) following a loud sound.
3
Functional measurements, such as maximal force and variability and speed of trajectories, remained unchanged after using the stimulation device in SCI survivors.

Research Summary

The study tested a wearable device that pairs auditory clicks with electrical stimulation to improve triceps muscle function in healthy volunteers and individuals with chronic cervical SCI. Results showed no significant changes in electrophysiological measurements or functional outcomes related to triceps function after using the device in either healthy volunteers or SCI survivors. The findings suggest the triceps muscle may be less amenable to plasticity induced by paired stimulation compared to other muscles like the biceps, potentially explaining its poorer recovery after SCI.

Practical Implications

Muscle-Specific Plasticity

The study highlights that different muscles may respond differently to stimulation protocols aimed at inducing plasticity, suggesting muscle-specific approaches may be necessary for motor recovery.

Limited Triceps Plasticity

The results indicate that the triceps muscle may have limited potential for plasticity compared to the biceps, which has implications for rehabilitation strategies targeting elbow extension after SCI.

Rethinking Stimulation Protocols

The failure of paired stimulation to improve triceps function suggests a need to explore alternative stimulation protocols or therapeutic interventions to enhance triceps recovery after spinal cord injury.

Study Limitations

1
Variable compliance among SCI participants in using the wearable device may have affected the results.
2
The CUE questionnaire's focus on hand and finger function may not have been sensitive enough to detect changes in triceps function.
3
The heterogeneity of SCI participants, including both complete and incomplete injuries, introduced variability in the data.

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