Abstract
Study design
Randomised, controlled, crossover study.
Objectives
Paired corticospinal–motoneuronal stimulation (PCMS) involves repeatedly pairing stimuli to corticospinal neurones and motoneurones to induce changes in corticospinal transmission. Here, we examined whether PCMS could enhance maximal voluntary elbow flexion in people with cervical spinal cord injury.
Setting
Neuroscience Research Australia, Sydney, Australia.
Methods
PCMS comprised 100 pairs of transcranial magnetic and electrical peripheral nerve stimulation (0.1 Hz), timed so corticospinal potentials arrived at corticospinal–motoneuronal synapses 1.5 ms before antidromic motoneuronal potentials. On two separate days, sets of five maximal elbow flexions were performed by 11 individuals with weak elbow flexors post C4 or C5 spinal cord injury before and after PCMS or control (100 peripheral nerve stimuli) conditioning. During contractions, supramaximal biceps brachii stimulation elicited superimposed twitches, which were expressed as a proportion of resting twitches to give maximal voluntary activation. Maximal torque and electromyographic activity were also assessed.
Results
Baseline median (range) maximal torque was 11 Nm (6–41 Nm) and voluntary activation was 92% (62–99%). Linear mixed modelling revealed no significant differences between PCMS and control protocols after conditioning (maximal torque: p = 0.87, superimposed twitch: p = 0.87, resting twitch: p = 0.44, voluntary activation: p = 0.36, biceps EMG: p = 0.25, brachioradialis EMG: 0.67).
Conclusions
Possible explanations for the lack of effect include a potential ceiling effect for voluntary activation, or that PCMS may be less effective for elbow flexors than distal muscles. Despite results, previous studies suggest that PCMS is worthy of further investigation.
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Acknowledgements
We acknowledge Dr James Nuzzo, Zoë Djajadikarta, Harrison Finn and Dr Euan McCaughey for their assistance during experiments, and acknowledge participants for their contributions to the study.
Funding
This study was supported by a Program Grant (1055084) from the National Health and Medical Research Council of Australia (NHMRC).
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SCD and JLT conceived the work, and SCD, CLBR, JEB and JLT designed the work. SCD and CLBR acquired data and SCD, CLBR, JEB and JLT played an important role in interpreting the results. SCD drafted the manuscript and SCD, CLBR, JEB and JLT revised the manuscript. SCD, CLBR, JEB and JLT approved the final version and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
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We certify that all applicable institutional and governmental regulations concerning the ethical use of human volunteers were followed during the course of this research. Procedures were approved by the Human Research Ethics Committee of the University of New South Wales (approval number HC12556). The study was conducted according to the Declaration of Helsinki but was not registered in a publicly accessible database prior to participant recruitment.
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Dongés, S.C., Boswell-Ruys, C.L., Butler, J.E. et al. The effect of paired corticospinal–motoneuronal stimulation on maximal voluntary elbow flexion in cervical spinal cord injury: an experimental study. Spinal Cord 57, 796–804 (2019). https://doi.org/10.1038/s41393-019-0291-3
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DOI: https://doi.org/10.1038/s41393-019-0291-3
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