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Analyzing Activity and Injury: Lessons Learned from the Acute:Chronic Workload Ratio

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Abstract

Injuries occur when an athlete performs a greater amount of activity than what their body can withstand. To maximize the positive effects of training while avoiding injuries, athletes and coaches need to determine safe activity levels. The International Olympic Committee has recommended using the acute:chronic workload ratio (ACWR) to monitor injury risk and has provided thresholds to minimize risk when designing training programs. However, there are several limitations to the ACWR and how it has been analyzed which impact the validity of current recommendations and should discourage its use. This review aims to discuss previously published and novel challenges with the ACWR, and strategies to improve current analytical methods. In the first part of this review, we discuss challenges inherent to the ACWR. We explain why using a ratio to represent changes in activity may not always be appropriate. We also show that using exponentially weighted moving averages to calculate the ACWR results in an initial load problem, and discuss their inapplicability to sports where athletes taper their activity. In the second part, we discuss challenges with how the ACWR has been implemented. We cover problems with discretization, sparse data, bias in injured athletes, unmeasured and time-varying confounding, and application to subsequent injuries. In the third part, conditional on well-conceived study design, we discuss alternative causal-inference based analytical strategies that may avoid major flaws in studies on changes in activity and injury occurrence.

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Fig. 1

(reproduced from Gabbett [8], with permission)

Fig. 2

(reproduced from Menaspà [25], with permission)

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Authors and Affiliations

  1. Centre for Clinical Epidemiology, Lady Davis Institute, Jewish General Hospital, McGill University, 3755 Côte Ste-Catherine Road, Montreal, QC, H3T 1E2, Canada

    Chinchin Wang & Ian Shrier

  2. Department of Epidemiology, Biostatistics and Occupational Health, McGill University, 1020 Pine Avenue West, Montreal, QC, H3A 1A2, Canada

    Chinchin Wang

  3. Department of Mathematics and Statistics, McGill University, 805 Sherbrooke Street West, Montreal, QC, H3A 0B9, Canada

    Jorge Trejo Vargas, Tyrel Stokes & Russell Steele

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  1. Chinchin Wang
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Correspondence to Ian Shrier.

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No sources of funding were used to assist in the preparation of this article. Chinchin Wang is partially supported through a grant from the Canadian Institutes of Health Research.

Conflict of Interest

Chinchin Wang, Jorge Trejo Vargas, Tyrel Stokes, Russell Steele, and Ian Shrier declare that they have no conflicts of interest relevant to the content of this review.

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Wang, C., Vargas, J.T., Stokes, T. et al. Analyzing Activity and Injury: Lessons Learned from the Acute:Chronic Workload Ratio. Sports Med 50, 1243–1254 (2020). https://doi.org/10.1007/s40279-020-01280-1

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