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The use of the acute:chronic workload ratio (A/C) has received a growing interest in the past 2 years to monitor injury risk in a variety of team sports.1 ,2 This ratio is generally computed over 28 days (ie, load accumulated during the current week/load accumulated weekly over the past 28 days), using both internal (session-rate of perceive exertion (Session-RPE)×duration) and external (tracking variables, often Global Positioning System (GPS)-related, such as high-speed running and acceleration variables) measures of competitive and training load. While the potential benefit of such a metric is straight forward for practitioners, there remain several limitations to (1) the assessment of relative external load and in turn, injury risk in players differing in locomotor profiles and (2) the effective monitoring of overall load across all training and matches throughout the year. In turn, these limitations likely compromise the usefulness of the A/C ratio in elite football (soccer).
Assessing player's locomotor profile and relative external load.
Speed: Considering that subtle differences in sprinting intensity such as high (85–95% of maximal sprinting speed) versus very high-speed running (>95%) may have important implications with regard to injury risk and prevention,3 the individualisation of high-speed running zones may be important. However, such a sprint-intensity classification requires the use of players' maximal sprinting speed as a reference, which is very rarely assessed in elite players. Therefore, considering the large variations in locomotor profiles between players within the same team, the use of absolute (fixed) speed thresholds to define high-speed running zones may limit the sensitivity of the A/C ratio with respect to high-speed running load3 and in turn, injury risk.
Fitness: Considering that fitness testing (eg, maximal aerobic speed) is also rare in professional football, and considering the clear impact of fitness on injury risk,4 it is difficult to …