REF-365 · Impellizzeri et al., 2020 (ACWR critique) + Hulin et al., 2016 (ACWR original) · International Journal of Sports Physiology and Performance, · Paper
Acute:Chronic Workload Ratio (ACWR)
Originally proposed, now without supporting evidence for injury management
Original Claim (Hulin 2016 and the early ACWR literature; not checked against a source here)
The ratio of acute (7-day) to chronic (28-day) load was proposed to predict injury, with a "sweet spot" of moderate ratios and elevated risk after "spikes".
Developed in rugby, cricket and Australian football.
Critique (Impellizzeri 2020 — what the abstract says)
Recommending that coaches manipulate ACWR assumes a causal effect on injury, and no study has even tried to estimate causal effects properly — so manipulating ACWR to change injury rates "remains a conjecture and an overinterpretation".
Ratio data carry known problems and unrecognised assumptions: ACWR is an inaccurate metric (it fails to normalise the numerator by the denominator even when uncoupled), lacks a rationale for a causal role, is ambiguous, and is not consistently and unidirectionally related to injury risk.
It adds noise and creates statistical artefacts.
Conclusion: no evidence supports using ACWR inside training-load management systems or in training recommendations meant to lower injury risk.
Key Findings — Current State
No evidence supports ACWR-based rules for reducing injury. Treat an ACWR number as a description of how load changed, not as a risk score or a target.
Practical Application
Impellizzeri and colleagues conclude that no study has estimated a causal effect of the acute:chronic workload ratio on injury, that the ratio is an inaccurate, ambiguous metric that creates statistical artefacts, and that there is no evidence supporting its use in load management or injury-prevention recommendations — do not steer training by an ACWR "sweet spot" or spike threshold.
Subjective wellness, HRV and load read together as context is the base's general practice, not a finding of this paper.
Limitations
A commentary: it argues from methods and published data, it does not present new data.
Evidence base it critiques is mostly team-sport; endurance-specific ACWR data are thinner still.
How this entry was checked and changed
Why this level
regraded 2026-09-27 from B: methodological commentary, expert opinion, no data
Content correction 2026-09-27
Type "Methodology RCT + critique" -> conceptual commentary with no data; Level B -> C.
"ACWR remains a useful heuristic" and "EWMA / rolling metrics more statistically sound" -> the abstract concludes there is no evidence supporting ACWR for load management or injury reduction; alternative metrics are not endorsed in it.
Practical rules "avoid >30-40% jumps", "<30% week-over-week", "re-build over 2-3 weeks" and CTL/ATL/TSB as proxies removed -> not from this paper.
Hulin's sweet-spot numbers (0.8-1.3, >1.5) removed -> no DOI for the original claim in this entry; described qualitatively instead. Sport "cycling" -> general.
2026-09-28: added Journal line from the Europe PMC record (Europe PMC/PubMed PMID 32502973).