ACWR

ACWR, or Acute:Chronic Workload Ratio, is a metric used in sports science to quantify the relationship between recent training load and longer-term training history. It is intended to help guide training adjustments and injury risk management by highlighting load spikes relative to an athlete’s recent history.

Calculation typically involves two components. The acute workload is the sum of load in a short, recent window (commonly 7 days). The chronic workload is the sum of load in a longer rolling window (commonly 28 days). The ACWR is the ratio of acute to chronic load. Load can be measured as external workload (such as distance, sessions, velocity, or accelerations) or internal workload (such as session-RPE or other perceived effort measures). Variations in window length and load type exist in practice.

Interpretation centers on balance and spikes. A value near 1 suggests the current week’s load aligns with recent history. Values well above 1 indicate a spike in acute load relative to chronic load, while values well below 1 indicate a drop. In some studies and practical guidelines, spikes above 1.5 or declines below 0.8 are highlighted as potential risk indicators, but thresholds are not universal and evidence for consistent injury prediction is mixed.

Critically, ACWR has limitations. Critics point to statistical concerns such as mathematical coupling, dependence on chosen time windows, and sensitivity to how loads are measured. Trauma risk appears to be multifactorial, and ACWR should not be used in isolation. It is commonly integrated with other workload metrics, athlete wellness, and performance data within a broader load-management framework.

History and usage: The concept gained prominence in the 2010s and remains widely used with ongoing debate about its predictive value and best practices.