The Individual and Combined Effects of Multiple Factors on the Risk of Soft Tissue Non-contact Injuries in Elite Team Sport Athletes

Esmaeili, A., Hopkins, W.G., Stewart, A.M., Elias, G.P., Lazarus, B.H., Aughey, R.J.

Aim: Relationships between athlete monitoring-derived variables and injury risk have
been investigated predominantly in isolation. The aim of this study was to evaluate the
individual and combined effects of multiple factors on the risk of soft-tissue non-contact
injuries in elite team sport athletes.
Methods: Fifty-five elite Australian footballers were prospectively monitored over two
consecutive seasons. Internal and external training load was quantified using the session
rating of perceived exertion and GPS/accelerometry, respectively. Cumulative load and
acute-to-chronic workload ratios were derived using rolling averages and exponentially
weighted moving averages. History of injuries in the current and previous seasons was
recorded along with professional experience, weekly musculoskeletal screening, and
subjective wellness scores for individual athletes. Individual and combined effects of
these variables on injury risk were evaluated with generalized linear mixed models.
Results: High cumulative loads and acute-to-chronic workload ratios were associated
with increased risk of injuries. The effects for measures derived using exponentially
weighted moving averages were greater than those for rolling averages. History of a
recent injury, long-term experience at professional level, and substantial reductions in a
selection of musculoskeletal screening and subjective wellness scores were associated
with increased risk. The effects of high cumulative loads were underestimated by

∼20% before adjusting for previous injuries, whereas the effects of high acute-to-
chronic workload ratios were overestimated by 10–15%. Injury-prone players, identified

via player identity in the mixed model, were at > 5 times higher risk of injuries
compared to robust players (hazard ratio 5.4, 90% confidence limits 3.6–12) despite
adjusting for training load and previous injuries. Combinations of multiple risk factors
were associated with extremely large increases in risk; for example, a hazard ratio
of 22 (9.7–52) was observed for the combination of high acute load, recent history
of a leg injury, and a substantial reduction in the adductor squeeze test score.

Esmaeili et al. Effects of Multiple Injury Risk Factors

Conclusion: On the basis of our findings with an elite team of Australian footballers,
the information from athlete monitoring practices in team sports should be interpreted
collectively and used as a part of the injury prevention decision-making process along
with consideration of individual differences in risk.

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