Impellizzeri et al. 2020, Acute:chronic workload ratio conceptual issues and pitfalls

Impellizzeri, Tenan, Kempton, Novak & Coutts, International Journal of Sports Physiology and Performance 15(6):907-913, DOI 10.1123/ijspp.2019-0864. Critical methodological review of the acute:chronic workload ratio (ACWR). Identifies statistical artefacts from the ratio construction (mathematical coupling of acute and chronic terms, spurious correlation), discretisation of a continuous variable into arbitrary ‘sweet spot’ bands, and the unjustified causal inference required to use the ratio for load prescription. Concludes there is no sound evidence supporting ACWR for training-load management or injury-risk reduction. The authors and colleagues separately argued the widely reproduced ACWR-injury ‘sweet spot’ figure is flawed. Strong as a critique (conceptual and statistical argument, not an empirical injury trial).