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Mathematical coupling causes spurious correlation within the conventional acute-to-chronic workload ratio calculations
  1. Lorenzo Lolli1,
  2. Alan M Batterham1,
  3. Richard Hawkins2,
  4. David M Kelly2,3,
  5. Anthony J Strudwick2,
  6. Robin Thorpe2,3,
  7. Warren Gregson3,
  8. Greg Atkinson1
  1. 1 Health and Social Care Institute, Teesside University, Middlesbrough, UK
  2. 2 Medicine and Science Department, Manchester United Football Club, Manchester, UK
  3. 3 Football Exchange, Research Institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, UK
  1. Correspondence to Lorenzo Lolli, School of Health and Social Care, Health and Social Care Institute, Teesside University, Middlesbrough TS1 3BA, UK; L.Lolli{at}

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The monitoring of training loads is now a much-researched topic in team sports.1 Within this topic, researchers and practitioners are particularly interested in the impact of relatively short (acute) periods of higher training loads normalised for the prior and longer term (chronic) loads. In recent years, a well-established approach for normalising this acute ‘spike’ to chronic load has been by calculating the ‘acute:chronic workload ratio’ (ACWR). Importantly, the term "load" was retained given its common use in this research area. Both this index and chronic load itself have been reported to be independent predictors of training-related injuries.2 It has also been reported, particularly in team sports competitors, that there are associations between acute spikes in training loads (relative to chronic loads) and time-loss injuries.1

The ACWR is usually calculated as the simple ratio of recent (ie, 1 week) to longer term (ie, 4 weeks) training loads.1 While it is important for the numerator and denominator of any ratio to be correlated only through biological mechanisms,3 one aspect of the ACWR calculation is that the acute load also constitutes a substantial part of the chronic load. …

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  • Contributors LL and GA developed the article concept. All authors contributed to write, provide feedback and revise the manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.