Original researchRelationship between interchange usage and risk of hamstring injuries in the Australian Football League
Introduction
The hamstring strain is one of the most common injuries in sports which involve sprinting, including track events (such as the 100 m sprint) and the various football codes. Hamstring injuries are the most common injury in the Australian Football League (AFL) and are responsible for the highest number of matches missed through injury.1 Hamstring injuries generally occur acutely from a high intensity event (as per the 100 m sprinter tearing the muscle after 40 m of running) during a match or training session or, less commonly, as a gradual onset injury with specific onset hard to isolate. A slight majority of hamstring injuries in the AFL occur in matches although some occur during training sessions or are of unknown/insidious onset. Known risk factors for hamstring injury include player age,2, 3 past history of hamstring injury, strength deficits, indigenous race and past history of other injury (including calf, knee, ankle and groin injuries).4, 5, 6
The use of the interchange bench in AFL football changed over the period 2003–2010 despite fairly constant rules. In these years the game was played between two teams of 18 players, with four players on an interchange bench and with unlimited rotations (interchanges) of players allowed. In 2006, rule changes were introduced to increase the continuity of the game to improve the spectacle of the event, which had an effect of reducing the amount of rest time for players after a score or an umpiring decision. In addition to these changes, umpires have been instructed to try to increase the continuity of the game by decreasing the amount of time taken to bounce the ball and throw the ball in from the boundary line. Although there has been a basic 80 min of time ‘in play’ over these eight seasons, the continuity of the game has varied, partly because of the 2006 rule changes and partly due to changes in the number of stoppages which otherwise occur (e.g. scoring plays, boundary throw ins, ball-ups). The actual length of games is approximately 120 min due to the substantial time added for stoppages. In the background of these changes to game continuity, there was a substantial increase in the number of interchange movements being made by teams during games over the eight year period between 2003 and 2010 (online Table 4). Teams made fewer than 30 interchanges per game in 2003 but greater than 100 interchanges per game in 2010.
Fatigue has previously been cited as a risk factor for injury in team sport.7, 8 It is plausible that increased average player speed9, 10 and increased player fatigue are both independent risk factors for hamstring strain. The level of both risk factors are likely to be influenced by the number of player interchanges. The aim of this study was to assess risk factors for hamstring strain in the AFL. In particular, it was aimed to assess the impact that changes in interchange movements and game time may have had on the risk of hamstring strain in the AFL, corrected for other known risk factors.
Section snippets
Methods
The methods used in this study are similar to a previously conducted study in the AFL examining intrinsic and extrinsic risk factors for hamstring strain, although in this study a more sophisticated multivariate technique was used.3 Injury data collected between 2003 and 2010 inclusive were extracted from the AFL injury database for analysis. Match performance statistics obtained from the official statistical providers for the AFL (Champion Data, Melbourne, Australia) were also analyzed. We
Results
Over each of the eight seasons from 2003 to 2010 the total numbers of listed players at all 16 AFL clubs combined were respectively 676, 685, 692, 702, 708, 713, 738 and 742. They suffered a total of 899 hamstring strains during the home and away seasons over the eight years (Table 1). However, only 416 were confirmed as occurring during a regular season AFL grade match from rounds 2–21. The number of interchanges per match (for both teams) steadily increased by a substantial amount each year (
Discussion
Hamstring injuries in the AFL have been studied extensively. This study confirmed previous findings that recent hamstring strain, past ACL reconstruction5 and past calf injury3 are all risk factors for hamstring strain.2, 18 It is the first study to examine the effects of match characteristics on the risk of hamstring injury.
Increasing interchanges by the opposition increased the risk of hamstring injury in an individual, and where the opposition made more than 60 interchanges in a game there
Conclusion
This study suggests that AFL players who do not regularly interchange off the field are slightly more prone to hamstring injury over the coming weeks and that an increasing number of interchanges by the opposition also increases individual risk of hamstring injury. The protective effect of individual rest is not enough to offset the increased risk to other players on the field when there are increased numbers of interchange movements. It is plausible that a combination of increased game speed
Practical implications
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Individual athletes are somewhat protected against hamstring injury in the AFL by having a break on the interchange bench. This suggests that fatigue may be a risk factor for hamstring injury.
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When opposition interchanges increase, a player's risk of hamstring injury increases. This suggests that running speed (particularly running speed of one's opponent) may also be a risk factor for hamstring injury.
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The protective effect of interchange for individuals is not enough to offset the increased
Acknowledgments
Kevin McGeechan is acknowledged for providing assistance with the SAS analysis. The Australian Football League (AFL) is acknowledged as the funding source for the AFL Injury database. Champion Data is acknowledged as the provider of match participation statistics. John Orchard is paid as a consultant to provide injury surveillance services for the AFL.
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