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Cross-education of muscular strength is facilitated by homeostatic plasticity

Abstract

Purpose

We examined the effect of priming the ipsilateral motor cortex (M1) using anodal transcranial direct current stimulation (tDCS) prior to a single bout of strength training on the cross-transfer of strength and corticospinal excitability and inhibition of the ipsilateral M1.

Methods

In a randomized double-blinded cross-over design, changes in strength and indices of corticospinal plasticity were analysed in 13 adults who were exposed to 20 min of ipsilateral anodal and sham tDCS (applied to the ipsilateral M1 to the training arm) followed by a single strength training session of the right Biceps Brachii only.

Results

The induction of homeostatic plasticity via anodal tDCS priming, significantly increased strength of the untrained left Biceps Brachii (12%) compared to sham tDCS (2%), increased corticospinal excitability (12–33%) and cross-activation (25%) when ipsilateral anodal tDCS was applied to the right M1 prior to a single session of strength training. Interestingly, ipsilateral sham tDCS and strength training resulted in an average increase in MEP amplitude of 2–32%.

Conclusion

The novel findings of this study include: priming the ipsilateral M1 via anodal tDCS prior to a single bout of strength training augments the cross-transfer of strength which is manifested by an increase in corticospinal excitability and cross-activation. These findings provide insight into how priming methods that induce homeostatic plasticity may be used to enhance the cross-education phenomenon.

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Abbreviations

1RM:

One-repetition maximum

Anodal tDCS + ST:

Anodal transcranial direct current stimulation and strength training

GABA:

γ-Aminobutyric acid

IHI:

Interhemispheric inhibition

MEPs:

Motor-evoked potentials

MMAX :

Maximum compound wave

MVIC:

Maximal voluntary isometric contraction

M1:

Primary motor cortex

NIBS:

Non-invasive brain stimulation

rmsEMG:

Root-mean square electromyography

sEMG:

Surface electromyography

Sham tDCS + ST:

Sham transcranial direct current stimulation and strength training

SICI:

Short-interval intracortical inhibition

ST:

Strength training

tDCS:

Transcranial direct current stimulation

TMS:

Transcranial magnetic stimulation

References

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Acknowledgements

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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Authors and Affiliations

Authors

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Correspondence to Ashlyn K. Frazer.

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Conflict of interest

None of the authors have potential conflicts of interest to be disclosed.

Additional information

Communicated by Toshio Moritani.

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Frazer, A.K., Williams, J., Spittle, M. et al. Cross-education of muscular strength is facilitated by homeostatic plasticity. Eur J Appl Physiol 117, 665–677 (2017). https://doi.org/10.1007/s00421-017-3538-8

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  • DOI: https://doi.org/10.1007/s00421-017-3538-8

Keywords

  • Cross-education
  • Homeostatic plasticity
  • Priming
  • Strength training
  • Transcranial direct current stimulation