Paired pulse transcranial magnetic stimulation in the assessment of biceps voluntary activation in individuals with tetraplegia

After a spinal cord injury (SCI), the nervous system undergoes changes, including cortical changes, impacting muscle function. Voluntary activation, which measures the neural drive to muscles, can be assessed using transcranial magnetic stimulation (TMS). However, this assessment faces technical challenges, such as stimulating the target muscle relative to its antagonist. The study explores whether using paired pulse TMS, which can modify muscle responses (MEPs), and looking at the MEP ratio between biceps and triceps muscles, could improve the accuracy of voluntary activation measurements (VATMS) in individuals with tetraplegia. The research found that paired pulse TMS did not significantly affect VATMS, and the MEP ratio did not influence VATMS in either the SCI or non-impaired groups. The linearity of the relationship between voluntary moment and superimposed twitch moment was lower in the SCI group, which complicates the interpretation of VATMS results.

• 1
  The main effect of the stimulation pulse (paired pulse compared to single pulse) on VATMS was not significant in the linear mixed-effects models in either the SCI or non-impaired groups.
• 2
  The MEP ratio was not modulated across all effort levels and did not affect VATMS in both groups for the stimulation parameters tested.
• 3
  Linearity of the voluntary moment and superimposed twitch moment relation was lower in SCI participants compared to non-impaired participants, limiting the interpretation of VATMS in the SCI group.