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Research Using Non-Invasive Sensors Identifies Altered Motor Unit Coordination After Incomplete Spinal Cord Injury

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Study Reveals Altered Muscle Coordination After Spinal Cord Injury

Researchers in Sweden have used non-invasive skin sensors to analyze changes in motor coordination following incomplete spinal cord injuries (SCI). The research, involving 25 participants, found differences in how nerve-to-muscle connections, known as motor units, work together in individuals with SCI compared to those without injury. The findings were published in the Journal of NeuroEngineering and Rehabilitation.

Study Overview and Methodology

The research team aimed to investigate motor unit coordination, which had not been previously examined in people with spinal cord injuries. The study involved 15 individuals with incomplete SCI and 10 control participants without injuries.

The methodology was non-invasive, utilizing high-density electromyography (HD-EMG). Sensors were placed on the skin surface to measure electrical activity in two calf muscles: the soleus and gastrocnemius. Participants were asked to push against a force measurement device at two different levels of voluntary effort: a light push (20% of maximum effort) and a moderate push (50% of maximum effort).

Key Findings

The analysis revealed distinct patterns of muscle activity at different exertion levels:

  • At 20% Effort: In the group with spinal cord injuries, fewer motor units in the calf muscles were activated in a shared, coordinated pattern compared to the control group. Researchers associated this reduced coordination with movements that were less stable.
  • At 50% Effort: The SCI group demonstrated stronger low-frequency synchronization between the two calf muscles. Researchers suggested this increased synchronization at higher effort could indicate a compensatory mechanism within the nervous system.

Researcher Interpretations

"At lower exertion levels, the muscles in participants with SCI were much less being driven by the same coordinated signal from the nervous system." — Zhihao Duan, Lead Author

Regarding the findings at 50% effort, Duan added, "This could be a sign of the nervous system compensating by sending louder, less refined signals."

Associate Professor Ruoli Wang, a senior researcher on the study, stated, "Our study reveals, at the cellular level, how the central nervous system adapts to the injury to control movement."

Wang noted one observation was that "after spinal cord injury the nervous system becomes more rigid and less able to change its approach as the muscles work harder," whereas a healthy nervous system can adapt its control strategy based on force demands.

Context, Limitations, and Potential Implications

The research was a collaboration between the Promobilia MoveAbility Lab at KTH Royal Institute of Technology and Aleris Rehab Station. Funding was provided by the Swedish Research Council and the Promobilia Foundation.

The researchers acknowledged two primary limitations:

  1. The study had a small sample size.
  2. The non-invasive surface measurement technique presented challenges in identifying a sufficient number of individual motor units per muscle.

Regarding potential applications, Ruoli Wang suggested the findings "may open the door to a new rehabilitation biomarker." This could assist clinicians and researchers in designing new neurorehabilitation strategies aimed at restoring coordinated neural input after spinal cord injury.