How could we forget injury mechanism and body area when considering the acute:chronic workload ratio relationship?

Are we forgetting crucial information around mechanism and body area when defining injuries for analysis? A post-script discussion piece on a recent editorial by Hulin¹ looking at the role of injury definitions in the workload & injury relationship.

WHAT INJURIES ARE YOU TRYING TO PREVENT?

Time-loss vs. Missed-match

Contact vs. Non-Contact

Upper body vs. Lower body

As performance is the ultimate goal in an elite setting, missed-match injuries that disrupt team dynamics would be the primary target for many. However, as highlighted by Hulin¹ (Figure 1), these types of injuries were not associated with changes in the acute:chronic workload ratio!

acute:chronic workload ratio

ACCOUNTING FOR MECHANISM AND BODY AREA

Equally as important, the mechanism of injury (contact vs. non-contact) and body area (upper vs. lower body) is often not considered in the acute:chronic workload ratio (ACWR) analysis. This poses the question as to whether a relative spike in workload (i.e. high ACWR) is associated with the incidence of a contact shoulder injury as the result of an opposition tackle. Anecdotally, non-contact injuries are more preventable from a workload and injury perspective and hence should be the primary focus. Furthermore, for sports involving high running demands, specifying the analysis to only include lower-body injuries may be more appropriate.

An abundance of research has investigated the workload & injury relationship across multiple sports, however, injury definitions have varied significantly. Subsequently, the implications derived from such research may be greatly influenced by the type of injuries targeted for prevention.

In this recent editorial, studies by Hulin et al² and Windt et al₃ were discussed, with worthy emphasis on the differing injury definitions in relation to duration and the subsequent ACWR relationship. However, the cited studies^{2 3} grouped contact and non-contact injuries. Furthermore, injuries to all body areas were considered the same.

The argument could be made that the ACWR, as derived from GPS-data in these studies, would not have predictive value for upper body contact injuries and therefore require further investigation to solidify these results.

WHAT IS STOPPING A REFINED ANALYSES TO CONSIDER MECHANISM AND BODY AREA?

Thinking fast⁴, I would argue statistical power. Dependent on the size of your data set (1,2,3,4+ seasons) the use of only missed-match injuries or sub-grouping injuries by mechanism/ body area may not meet statistical power guidelines and therefore must be noted as limitations in such settings. Furthermore, the depth of injury documentation to include all relevant information surrounding mechanism, body area, and type is crucial to facilitate this refined analyses. A possible solution is data sharing within codes to address statistical power. However, training structures, subsequent workload, and injury definitions may differ on a team-by-team basis.

CONDUCTING INVESTIGATIONS RELEVANT TO YOUR SPORT

Determining your most common injuries, specifically those associated with modifiable risk factors, is a key first step. For inclusion in the analysis it is important to consider:

1. Mechanism of injury (contact vs. non-contact). Anecdotally, non-contact injuries are likely more preventable from a workload and injury perspective.
2. Body area (upper vs. lower body). As a bare minimum, workload derived from GPS data should target lower body injuries, as the strength of the relationship is likely higher.
3. Injury severity (medical attention vs. time-loss vs. missed-match). Consider disruptions in training continuity (and chronic load) as a result of medical attention/ time-loss injuries. However, missed-match injuries are likely the most crucial and warrant primary investigation, as these can have the greatest impact on your chronic load foundation.

REFERENCES

1. Hulin BT. The never-ending search for the perfect acute:chronic workload ratio: what role injury definition? Br J Sports Med 2017. pii: bjsports-2016-097279.
2. Hulin BT et al. Low chronic workload and the acute:chronic workload ratio are more predictive of injury than between-match recovery time: a two-season prospective cohort study in elite rugby league players
3. Windt et al. Training load-injury paradox: is greater preseason participation associated with lower in-season injury risk in elite rugby league players? Br J Sports Med 2016. pii: bjsports-2016-095973
4. Kahneman, Daniel. Thinking, Fast and Slow. New York: Farrar, Straus and Giroux, 2011.

By Marcus Colby, ‎PhD Candidate at The University of Western Australia