Is there evidence for the asymmetrical transfer of strength to an untrained limb?

Vickie Wong; Jun Seob Song; Yujiro Yamada; Ryo Kataoka; William B Hammert; Robert W Spitz; Jeremy P Loenneke

doi:10.1007/s00421-024-05472-9

Is there evidence for the asymmetrical transfer of strength to an untrained limb?

Eur J Appl Physiol. 2024 Apr 3. doi: 10.1007/s00421-024-05472-9. Online ahead of print.

Authors

Vickie Wong¹, Jun Seob Song², Yujiro Yamada², Ryo Kataoka², William B Hammert², Robert W Spitz³, Jeremy P Loenneke⁴

Affiliations

¹ Department of Sport and Health, Solent University, Southampton, Hampshire, SO14 0YN, UK.
² Kevser Ermin Applied Physiology Laboratory, The University of Mississippi, University, P.O. Box 1848, University, MS, 38677, USA.
³ Department of Physiology and Biophysics, University of Mississippi Medical Center, Jackson, MS, USA.
⁴ Kevser Ermin Applied Physiology Laboratory, The University of Mississippi, University, P.O. Box 1848, University, MS, 38677, USA. jploenne@olemiss.edu.

PMID: 38568258
DOI: 10.1007/s00421-024-05472-9

Abstract

Purpose: The literature predominantly addresses cross-education of strength in the dominant limb rather than the non-dominant limb, guided by the hypothesis of an asymmetrical transfer of strength from unilateral training protocols. The purpose of the study was to review the literature and determine how much evidence was available to support this claim. A meta-analysis was performed to estimate the magnitude of this hypothesized asymmetrical transfer of strength.

Methods: A literature search of all possible records was implemented using Cochrane Library, PubMed, and Scopus from February 2022 to May 2022. Comparison of randomized controlled trials was computed. The change scores and standard deviations of those change scores were extracted for each group. Only three studies met the criteria, from which a total of five effect sizes were extracted and further analyzed.

Results: The overall effect of resistance training of the dominant limb on strength transfer to the non-dominant limb relative to the effects of resistance training the non-dominant limb on strength transfer to the dominant (non-training) limb was 0.46 (SE 0.42). The analysis from this study resulted in minimal support for the asymmetry hypothesis. Given the small number of studies available, we provide the effect but note that the estimate is unlikely to be stable.

Conclusion: Although it is repeatedly stated that there is an asymmetrical transfer of strength, our results find little support for that claim. This is not to say that it does not exist, but additional research implementing a control group and a direct comparison between limbs is needed to better understand this question.

Keywords: Asymmetry; Crossover; Exercise; Neural; Strength.