Figure 1: The U-Shape relationship between ACWR and injury risk (%) .
Practically this means that the ACWR can be monitored every day, for each athlete. The actual value of the ratio will have a practical significance, and with careful planning and alteration it can help to reduce the risk of injury. The ACWR value and its various meanings are listed below:
- < 0.80 (Under training and higher relative injury risk)
- 80 – 1.30 (Optimal workload and lowest relative injury risk – “The Sweet Spot”) .
- > 1.50 (The “danger zone” and highest relative injury risk)
It is important to note that these values are not ‘golden’ numbers, they will not apply to every athlete in every sport. An athlete’s prior training history, development, injury record, and level of participation will have a major influence on their training-load tolerance and subsequent injury risk. For example, a study conducted by Malone in professional soccer indicated a ‘sweet spot’ of between 1.00 – 1.25 for the lowest relative injury risk . This is similar, but different, to what was previously shown in rugby league (0.85 – 1.35) . Taking this into account, it is important to conduct some research into your sport in order to determine the injury risk ranges; with the best-case scenario being an in-house study of your athlete population. However, from the start of a new monitoring protocol, given the research that has been done to date and its findings, it will be safe to utilise the above ranges until more individualised, athlete-specific ranges (within your population) present themselves.
Training-Load Spikes and Injury
The process of analysing training-load data and calculating ACWR can yield helpful insight into training-load progression, particularly as it is a useful tool to view changes in workload over time. Because of this, research has now subsequently investigated this relationship and found that excessive and rapid increases in training-load are responsible for a large percentage of non-contact soft-tissue injuries [2, 10, 12, 17].
Thus, it is important to consider how week-to-week changes in training-load influence injury risk. In a study on Australian Rules football players, it was reported that 40% of injuries were associated with a rapid change (>10%) in weekly (i.e. acute) training-load compared to the previous week . Therefore, to minimize the risk of injury, practitioners may wish to limit weekly training-load increases to less than 10%.
High Chronic Loads and Injury Protection
The ACWR can not only be used to monitor athletes from day-to-day, but it can also be used during training-load planning and periodisation. Evidence suggests that both physically hard, and accumulated physically hard training (appropriately planned), may protect against injuries . For example, one study found that athletes with high chronic loads (fitness) had better protection against injuries when exposed to high acute training-loads .
From a practical standpoint, this means that if practitioners have a good understanding of the load that their athletes are going to experience in competition, they can plan training programmes in order to appropriately prepare them for these events. This, therefore, offers a protective effect against injury, and may theoretically lead to greater physical outputs and resilience in competition, as well as higher levels of athlete availability (i.e. having athletes available for training and competition) .