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No evidence of neural adaptations following chronic unilateral isometric training of the intrinsic muscles of the hand: a randomized controlled study

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European Journal of Applied Physiology Aims and scope Submit manuscript

Abstract

Purpose

To test whether long-term cortical adaptations occur bilaterally following chronic unilateral training with a simple motor task.

Methods

Participants (n = 34) were randomly allocated to a training or control groups. Only the former completed a 4-week maximal-intensity isometric training of the right first dorsal interosseus muscle through key pinching. Maximal strength was assessed bilaterally in four different movements progressively less similar to the training task: key, tip and tripod pinches, and handgrip. Transcranial magnetic stimulation was used to probe, in the left and right primary hand motor cortices, a number of standard tests of cortical excitability, including thresholds, intra-cortical inhibition and facilitation, transcallosal inhibition, and sensory-motor integration.

Results

Training increased strength in the trained hand, but only for the tasks specifically involving the trained muscle (key +8.5 %; p < 0.0005; tip +7.2 %; p = 0.02). However, the effect size was small and below the cutoff for meaningful change. Handgrip and tripod pinch were instead unaffected. There was a similar improvement in strength in the untrained hand, i.e., a cross-education effect (key +6.4 %; p = 0.02; tip +4.7 %; p = 0.007). Despite these changes in strength, no significant variation was observed in any of the neurophysiological parameters describing cortico-spinal and intra-cortical excitability, inter-hemispheric inhibition, and cortical sensory-motor integration.

Conclusions

A 4-week maximal-intensity unilateral training induced bilaterally spatial- and task-specific strength gains, which were not associated to direct or crossed cortical adaptations. The observed long-term stability of neurophysiological parameters might result from homeostatic plasticity phenomena, aimed at restoring the physiological inter-hemispheric balance of neural activity levels perturbed by the exercise.

Trial registration number

ClinicalTrials.gov identifier NCT02010398.

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Abbreviations

ANOVA:

Analysis of variance

CE:

Cross education

cM1:

Contra-lateral primary motor cortex

CMCT:

Central motor conduction time

CV:

Coefficient of variation

EMG:

Electromyography

FDI:

First dorsal interosseus

ICC:

Intra-class correlation coefficient

ICF:

Intra-cortical facilitation

IHI:

Inter-hemispheric inhibition

iM1:

Ipsi-lateral primary motor cortex

ISI:

Inter-stimulus interval

LAI:

Long-latency afferent inhibition

LICI:

Long-interval intra-cortical inhibition

LIHI:

Long-interval inter-hemispheric inhibition

MEP:

Motor-evoked potential

mV:

Millivolt

MVIC:

Maximum voluntary isometric contraction

RC:

Recruitment curve

RMT:

Resting motor threshold

SAI:

Short-latency afferent inhibition

SD:

Standard deviation

SEM:

Standard error of measurement

SICF:

Short-interval intra-cortical facilitation

SICI:

Short-interval intra-cortical inhibition

SIHI:

Short-interval inter-hemispheric inhibition

SRDi:

Individual smallest real difference

TMS:

Transcranial magnetic stimulation

TMStest:

1 mV MEP

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Acknowledgments

This study was partly supported by Fondazione Italiana Sclerosi Multipla (FISM Grant 2013/R/11) and by Fondazione Banco di Sardegna (FBS Grant 2014/0190).

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Author notes

    Authors and Affiliations

    1. Department of Biomedical Sciences, University of Sassari, Viale San Pietro 43/b, 07100, Sassari, Italy

      A. Manca, F. Ginatempo, M. P. Cabboi, B. Mercante, D. Dragone, E. R. De Natale & Franca Deriu

    2. Neurology Unit, “A. Segni” Hospital, ASL n. 1, Sassari, Italy

      E. Ortu

    3. Department of Physical Therapy, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, Israel

      Z. Dvir

    4. Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, London, UK

      J. C. Rothwell

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    1. A. Manca
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    Correspondence to Franca Deriu.

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    The authors declare no actual or potential conflict of interest.

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    All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

    Additional information

    Communicated by Guido Ferretti.

    A. Manca and F. Ginatempo have equally contributed to this work.

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    Manca, A., Ginatempo, F., Cabboi, M.P. et al. No evidence of neural adaptations following chronic unilateral isometric training of the intrinsic muscles of the hand: a randomized controlled study. Eur J Appl Physiol 116, 1993–2005 (2016). https://doi.org/10.1007/s00421-016-3451-6

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    • DOI: https://doi.org/10.1007/s00421-016-3451-6

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