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Methodological issues with the assessment of voluntary activation using transcranial magnetic stimulation in the knee extensors

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Abstract

Purpose

The assessment of voluntary activation of the knee extensors using transcranial magnetic stimulation (VATMS) is routinely performed to assess the supraspinal function. Yet methodological scrutiny of the technique is scarce. The aim of the present study was to examine face validity and reliability of VATMS and its two main determinants (superimposed twitch during a maximal voluntary contraction [SIT100%] and estimated resting twitch [ERT]).

Methods

SIT100%, ERT, and VATMS were measured on ten healthy males (age 24 ± 5 years) before and following intermittent isometric fatiguing exercise on two separate occasions.

Results

The findings indicated issues regarding the accuracy of ERT and suggested a three-point relationship should not be used to determine ERT. Reliabilities for VATMS, SIT100%, and ERT were acceptable pre- but much weaker post-exercise (especially for SIT100%). Despite statistically significant changes in main neuromuscular variables following the intermittent isometric fatiguing exercise (P < 0.05), when post-exercise reliability was considered, the exercise effect on VATMS was smaller than the smallest detectable change in 18 of the 20 individual tests performed, and for the whole sample for one of two visits. Finally, maximal voluntary contraction was reduced significantly following the neuromuscular assessment (NMA) pre-exercise but recovered during the NMA post-exercise.

Conclusion

This is the first study to demonstrate a lack of sensitivity of key neuromuscular measurements to exercise and to evidence both presence of neuromuscular fatigue following the NMA in itself, and recovery of the neuromuscular function during the NMA post-exercise. These results challenge the face validity of this routinely used protocol.

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Abbreviations

ERT:

Estimated resting twitch

ICC:

Intraclass correlation

KE:

Knee extensors

MEP:

Motor evoked potential

MVC:

Maximal voluntary contractions

NMA:

Neuromuscular assessment

POT:

Potentiated twitch force

SDC:

Smallest detectable change

SIT:

Superimposed twitch

SIT100% :

Superimposed twitch during a maximal voluntary contraction

TMS:

Transcranial magnetic stimulation

VA:

Voluntary activation

VATMS :

Voluntary activation using transcranial magnetic stimulation

VC:

Voluntary contraction

References

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Acknowledgements

The authors thank Dr. Rosie Twomey and Prof. Guillaume Millet for the valuable critical review of our manuscript.

Funding

No external funding was received for this work.

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Authors and Affiliations

Authors

Contributions

All authors contributed to the conception and design of the study. PA, AGT, JW, LS collected the data. All authors were involved in the analysis and interpretation of the data. JD, AGT and PA wrote the manuscript. All authors reviewed and approved the final version of the manuscript.

Corresponding author

Correspondence to Jeanne Dekerle.

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Conflict of interest

The authors report no conflict of interest for this work.

Additional information

Communicated by Nicolas Place.

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Dekerle, J., Ansdell, P., Schäfer, L. et al. Methodological issues with the assessment of voluntary activation using transcranial magnetic stimulation in the knee extensors. Eur J Appl Physiol 119, 991–1005 (2019). https://doi.org/10.1007/s00421-019-04089-7

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  • DOI: https://doi.org/10.1007/s00421-019-04089-7

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