Why are older Australian football players at greater risk of hamstring injury?

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Summary

Introduction

Increasing age is a commonly identified predictor of hamstring injury but is not modifiable to reduce injury risk. Why increasing age is a risk factor for hamstring injuries in athletes has not been studied to date. This study aimed to identify potentially modifiable age-related changes that predict hamstring injury in a population of Australian football players.

Methods

One hundred and one young (≤20 years), and 73 older (≥25 years), Australian football players, without a history of hamstring injury in the past 12 months were studied prospectively. Players underwent screening of anthropometric, flexibility and lower extremity range of movement tests during the pre-season period and were followed-up for a full season with respect to injury and match participation. Comparisons of the age groups were performed to identify differences related to age. Logistic regression analysis was undertaken to determine whether the observed differences were predictors of hamstring injury.

Results

There were significant differences between the age groups with respect to body weight, body mass index, hip flexor flexibility, hip internal rotation and ankle dorsiflexion range of movement. Body weight and hip flexor flexibility were significant independent predictors of hamstring injury in players aged ≥25 years. None of the observed differences were predictors of injury in the younger age group.

Conclusions

There are age-related changes that are potentially modifiable to reduce injury risk in older athletes and these factors should be considered in the development of hamstring injury prevention programs for this high risk group.

Introduction

Hamstring injuries are common in sprinting sports such as Australian football and soccer where the incidence is reported to be 12–16% of all injuries in a season.1, 2 Prevention of hamstring injuries is a key priority for sprinting sports due to the high incidence and rates of recurrence. An understanding of the risk factors for hamstring injury is crucial for the development of prevention strategies. The two most commonly identified risk factors for hamstring injury are a previous history of injury and increasing age.2, 3, 4, 5, 6, 7, 8 Unfortunately, neither of these factors is able to be modified to alter an athlete's risk of hamstring injury.

Recent studies have compared athletes who have and have not previously sustained hamstring injuries to establish the differences between these two groups. In particular, strength, flexibility, posture, neural mobility and other aspects of muscle function have been studied.9, 10, 11, 12 Unfortunately, the retrospective and cross-sectional nature of these studies do not allow conclusions to be drawn on whether the observed differences were present before injury or resulted from the injury. Similarly, studies that have used the uninjured leg for comparison12 assume that the measurements of the uninjured leg are independent of those on the injured leg which is not the case. As such, identifying modifiable factors associated with a previous history of hamstring injury is extremely difficult.

In contrast, increasing age, irrespective of past history, has been identified as a predictor of hamstring injury through five prospective cohort studies of Australian football and soccer players. Verrall et al. studied 114 elite Australian football players over one season and found that increasing age was an independent predictor of hamstring injury but did not define an age cut-off as age was analysed as a continuous variable.6 Arnason et al. demonstrated that the risk of hamstring injury increases by 10% per year in their study of 306 elite soccer players in Iceland.8 Orchard et al. investigated risk factors for lower extremity muscle strains over a 7 year period in the elite Australian Football League and found that players aged >23 years were at significantly elevated risk of hamstring injury.5 Similarly, elite Australian football players aged ≥25 years were over four times more likely to sustain a hamstring injury than those ≤20 years in the most recent prospective study involving 222 players.4 A prospective cohort study focussing on lower extremity injuries in community-level football found that players aged ≥23 years were almost four times more likely to sustain a hamstring injury during the season than players aged <23 years.4 Why the risk of hamstring injury increases at 23–25 years of age is not understood and has not been investigated to date.

The aims of this study were therefore to:

  • i.

    Compare younger (≤20 years) and older Australian football players (≥25 years) to determine whether any differences identified predict hamstring injury in older players.

  • ii.

    Determine whether there are any differences in intrinsic factors associated with increasing age that could be modified to reduce hamstring injury risk.

Section snippets

Methods

This study relates to two larger studies undertaken to identify risk factors for lower extremity injuries in elite and community-level Australian football players. A summary of the methodology, which was consistent for both cohorts, is provided here and the detailed methodology is published elsewhere.4, 13

Results

One hundred and seventy four players were included in this study, 135 elite and 39 community-level. Of these, 101 (58.0%) were aged 20 years or less and the remainder (n = 73, 42.0%) were aged 25 years or more. The cohort sustained 21 hamstring injuries during the season; 7 in the younger group (6.9% of younger group) and 14 (19.2% of older group) by older players. The unadjusted RR of sustaining a hamstring injury during the season in older players, without a history of hamstring injury in the

Discussion

Hamstring injuries are the most common injury sustained by elite and community-level Australian football players. Previous studies have highlighted the importance of age as a predictor for hamstring injury.2, 4, 5, 6, 8 Whilst age itself is not modifiable to reduce risk of injury, factors associated with ageing athletes have not been explored and previous authors have not provided potential explanations.2, 6, 8 Previously, we have suggested age-related changes to muscle structure and

Conclusions

Older Australian football players, without a history of a hamstring injury in the previous 12 months, are at significantly elevated risk of hamstring injury. This group of athletes was found to be significantly different to the group at lowest risk (aged 20 years or less) with respect to body weight, BMI, ankle dorsiflexion range of movement, hip flexor flexibility and active hip internal rotation range of movement. Multivariate modelling, adjusting for the level of competition and match time

Practical implications

  • Older Australian football players have a significantly elevated risk of hamstring injury, irrespective of their past history of hamstring injury, but the reasons for this are not known.

  • There are significant differences between players aged ≥ 25 years and those aged ≤ 20 years with respect to body weight, body mass index, hip flexor flexibility, hip rotation range of movement and ankle dorsiflexion range of movement.

  • Body weight and hip flexor flexibility are significant predictors of hamstring

Acknowledgments

The authors were supported by a Public Health Research Fellowship (BJG) and a Principal Research Fellowship (CFF) from the National Health and Medical Research Council of Australia, respectively. Funding for the elite study was provided by the Australian Football League Research and Development Board. The staff and players of the following football clubs are sincerely thanked: Collingwood; Essendon; Hampton Rovers; Hawthorn; Melbourne; Old Haileybury; Old Melburnians; Ormond; Richmond; and

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