Journal of Sports Science and Medicine
Journal of Sports Science and Medicine
ISSN: 1303 - 2968   
Ios-APP Journal of Sports Science and Medicine
Androit-APP Journal of Sports Science and Medicine
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©Journal of Sports Science and Medicine (2021) 20, 594 - 617   DOI: https://doi.org/10.52082/jssm.2021.594

Review article
The Calculation, Thresholds and Reporting of Inter-Limb Strength Asymmetry: A Systematic Review
Amy O. Parkinson1, , Charlotte L. Apps1, John G. Morris1, Cleveland T. Barnett1, Martin G. C. Lewis
Author Information
1 Nottingham Trent University, School of Science and Technology, Nottingham, United Kingdom
2 University of Derby, School of Human Sciences, Derby, United Kingdom

Amy O. Parkinson
✉ Nottingham Trent University, School of Science and Technology, Erasmus Darwin, Postgraduate Room 259, Clifton Campus, Nottingham, NG11 8NS, UK
Email: amy.parkinson@ntu.ac.uk
Publish Date
Received: 29-03-2021
Accepted: 28-06-2021
Published (online): 01-10-2021
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ABSTRACT

The prevalence of inter-limb strength differences is well documented in the literature however, there are inconsistencies related to measurement and reporting, and the normative values and effects associated with inter-limb asymmetry. Therefore, the aims of this systematic review were to: 1) assess the appropriateness of existing indices for the calculation of asymmetry, 2) interrogate the evidence basis for literature reported thresholds used to define asymmetry and 3) summarise normative levels of inter-limb strength asymmetry and their effects on injury and performance. To conduct this systematic review, scientific databases (PubMed, Scopus, SPORTDiscus and Web of Science) were searched and a total of 3,594 articles were retrieved and assessed for eligibility and article quality. The robustness of each identified asymmetry index was assessed, and the evidence-basis of the identified asymmetry thresholds was appraised retrospectively using the references provided. Fifty-three articles were included in this review. Only four of the twelve identified indices were unaffected by the limitations associated with selecting a reference limb. Eighteen articles applied a threshold to original research to identify “abnormal” asymmetry, fifteen of which utilised a threshold between 10-15%, yet this threshold was not always supported by appropriate evidence. Asymmetry scores ranged between and within populations from approximate symmetry to asymmetries larger than 15%. When reporting the effects of strength asymmetries, increased injury risk and detriments to performance were often associated with larger asymmetry, however the evidence was inconsistent. Limitations of asymmetry indices should be recognised, particularly those that require selection of a reference limb. Failure to reference the origin of the evidence for an asymmetry threshold reinforces doubt over the use of arbitrary thresholds, such as 10-15%. Therefore, an individual approach to defining asymmetry may be necessary to refine robust calculation methods and to establish appropriate thresholds across various samples and methodologies that enable appropriate conclusions to be drawn.

Key words: Imbalance, power, functional performance, between-limb, injury, performance


           Key Points
  • Only four of the twelve identified asymmetry indices were able to overcome the limitations associated with selecting a reference limb or value
  • Interpretation of asymmetry scores using pre-determined thresholds, such as 10-15%, may be unfounded as many lack a solid evidence base
  • The magnitude of inter-limb strength asymmetry varies from approximate symmetry to greater than 15% asymmetry, however there are inconsistent findings regarding the magnitude of asymmetry in similar participant groups and the subsequent effects of asymmetry on injury and performance
  • Disparate findings can be attributed to differences in methodology, including asymmetry calculation and threshold application
  • Going forward, an individualised approach to asymmetry may be necessary, which considers the use of sample-specific thresholds and individual variability
 
 
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