Original researchGround hardness and injury in community level Australian football
Introduction
Current climatic changes around the globe have focused attention on the potential sporting injury risks associated with extreme conditions of sport surfaces.1 Under drought conditions, for both safety and grounds management imperatives, perhaps the most concerning aspect of ground conditions are hard, dry grounds. Ground hardness refers to the effect that the ground has on absorbing impact forces2 and this surface characteristic has increasingly been associated with injuries on natural turf playing grounds.3, 4, 5 The contribution of hard grounds to injury risk is postulated to arise through two mechanisms. Firstly, a harder ground provides greater peak reaction forces when a player either lands or applies a force to it than occurs on a softer ground, potentially increasing the risk of injuries, such as fractures or non contact overuse injuries.6 Secondly, hard grounds enable faster game speeds potentially increasing the risk of a higher collision impact either with another player or the ground itself.7
Many studies have identified ground and environmental conditions as factors associated with injury, particularly in the football codes of Australian football (AF),2, 8 American football,9, 10 rugby union5, 11 and rugby league.3, 12 Fractures, strains/sprains and haematomas are the most commonly reported injury types related to hard grounds.3, 8, 11 Hard grounds have been more commonly associated with the hot months of the year and hence have also been linked with the notion of an ‘early season bias’ in injury occurrence for winter-based sports, that is with more injuries being sustained at the beginning of the season.4 This has been supported in studies in AF,13 American football,9 rugby union14 and Gaelic football.15 As an early season bias has also been reported for indoor court surfaces,16 it is likely that intrinsic factors, such as inadequate player conditioning or an increased exposure to competitive game conditions are also partially responsible for the increase in injuries in the early part of the season.17
A limitation of the research to date is what is subjectively perceived and often cited as ‘ground condition’ is likely to be related to a variety of physical quantitative measurements such as hardness, traction, grass cover, and volumetric moisture content. In addition, the risk of different types of injuries may be mechanistically linked to different surface properties or different combinations of surface properties, with ground hardness being just one measurable surface property. Another issue with many of the published studies linking hard grounds and injury risk is the subjective nature of their classification of ground conditions. For example, relying on completion of a simple check box assessment used by coaches and support staff to record against a list of options such as hard or soft, wet or dry, muddy or firm.9
Whilst subjective observational assessments can provide a general indication of ground conditions, they are unable to quantify the actual degree of hardness and the reliability of such subjective classifications remains unknown. Rather surprisingly, the use of objective hardness measures, obtained from instrumented testing devices, has only been previously reported in three injury studies in AF7, 18 and one in rugby union.5 There was no significant overall relationship between ground hardness and risk of anterior cruciate ligament injuries in elite AF, but there was a trend towards an increased risk when the ground was harder.18 There was also no significant relationship between hard ground and community-level rugby union injuries in New Zealand.5
All four studies that reported quantitative ground condition measures used penetrometers, a device first developed for the rating of horse racing tracks, to assess ground hardness and subsequently related these measures to the injuries sustained. Whilst the penetrometer has been acknowledged as a suitable objective assessment of soil strength, it may not be valid in determining the hardness on the surface due to the depth of penetration of the device,19 which may help to explain a lack of significant findings. The Clegg hammer has been accepted as a more useful and reliable device for measuring ground hardness20, 21 and its’ measures correlate more closely to player perceptions of hardness, compared with those from a penetrometer.21, 22 To date, no study has reported the relationship between prospectively collected injury data and ground hardness using the Clegg hammer in any sport.
The evidence linking ground hardness to injury risk has been somewhat inconclusive, often limited to elite players and based on either subjective opinion or sub-optimal testing devices. The purpose of this study was to describe the risk associated with ground hardness and prospectively collected injury data. In addition, it identifies the nature, mechanisms and severity of injuries according to different levels of ground hardness and provides the first profile of the relationship between ground conditions for community-level AF.
Section snippets
Methods
Details of all injuries sustained by players from 40 community AF teams in Victoria (VIC) and Western Australia (WA), during the 2007 and 2008 playing seasons, were prospectively collected as part of a large randomised controlled trial called Preventing Australian Football Injuries through eXercise (PAFIX).23 This included 10 senior grade and 10 reserve grade teams in VIC and 8 senior, 7 reserve and 5 colt (under 19) grade teams in WA over the 2-year period. Full details of the study protocol
Results
A total of 402 injuries were recorded on the assessed grounds: 165 in the 2007 season and 237 in the 2008 season. The exact location of the injury incident on the ground was unknown for 50 injuries, and so only 352 injuries were able to be related to ground hardness. The overall rate of injury was 39.2 injuries per 1000 playing hours (95%CI: 35.2–43.3).
The Clegg hammer readings from all test locations ranged from 25 to 301 g across the two seasons. Clegg hammer hardness categories from
Discussion
This is the first study to investigate the link between injury and ground hardness using the Clegg hammer, as an objective measure of hardness. Moreover, it is the first study of its type to focus on community level AF. Despite the fact that unacceptably high Clegg hammer hardness readings were recorded from a low number of locations and only a few injuries occurred at these locations, the percentage risk and relative risk of injury was significantly higher on unacceptably hard locations
Conclusions
This study is the first study to directly match Clegg hammer hardness measures with prospective injury data in any sport and present a description of the injuries sustained and the relative risk of injury on different levels of ground hardness. Despite the low number of injuries, the risk of sustaining an injury on low/normal and unacceptably hard grounds was significantly greater than on the preferred (optimum) range of hardness. Notably, the severity of injuries on unacceptably hard grounds
Practical implications
- •
Linking injury data to objectively measured ground hardness at the specific location on the playing field allows a more accurate assessment of the association.
- •
The Clegg hammer is a valuable tool for objectively measuring ground hardness.
Acknowledgements
The PAFIX study was funded by a nationally competitive research grant from the (Australian) National Health and Medical Research Council (NH&MRC) – Project ID 400937. Authors DT and TD were funded by research fellowships through this grant. CFF was supported by an NHMRC Principal Research Fellowship (ID: 565900). Additional project funds were provided by the Sport and Recreation Victoria portfolio of the Department for Victorian Communities. The Australian Centre for Research into Injury in
References (30)
- et al.
Influence of environmental and ground conditions on injury risk in rugby league
J Sci Med Sport
(2007) - et al.
Incidence and risk factors for injury in non-elite Australian football
J Sci Med Sport
(2004) The AFL penetrometer study: work in progress
J Sci Med Sport
(2001)- et al.
Injury in junior Australian Rules footballers
J Sci Med Sport
(2003) - et al.
Safe physical activity environments – to what extent are local government authorities auditing the safety of sporting grounds
ACHPER Healthy Lifestyles J
(2009) - et al.
Rainfall, evaporation and the risk of non-contact anterior cruciate ligament injury in the Australian football league
Med J Aust
(1999) - et al.
An analysis of injury rates after season change in rugby league
Clin J Sports Med
(2006) Is there a relationship between ground and climatic conditions and injuries in football
Sports Med
(2002)- et al.
Association of ground hardness with injuries in rugby union
Br J Sports Med
(2007) - et al.
Shoe–surface interaction and the reduction of injury in rugby union
Sports Med
(1998)
Evidence for the aetiology of injuries in Australian football
Br J Sports Med
Australian Rules football injuries in children and adolescents
Med J Aus
High school football injuries: field conditions and other factors
Wisc Med J
A review of selected noncontact anterior cruciate ligament injuries in the National Football League
Foot Ankle Int
Schoolboy rugby injuries, 1969–1986
Med J Aust
Cited by (28)
Concussion incidence and time-loss in Australian football: A systematic review
2020, Journal of Science and Medicine in SportCitation Excerpt :As such, the criteria used to quantify concussions across the included studies have nuances that are unaccounted for and prevented meaningful comparisons from being made with a meta-analytic approach; a narrative synthesis was therefore conducted. The final selection of 42 articles included 16 AFL-IRs;4–19 18 articles on injury surveillance;33–50 six empirical articles that reported concussion incidence,20,51–55 and two that reported head-impact exposure. 21,56 All players participated in AF in Australia.
Mechanisms for regulating step length while running towards and over an obstacle
2016, Human Movement ScienceCan the natural turf pitch be viewed as a risk factor for injury within Association Football?
2016, Journal of Science and Medicine in SportCitation Excerpt :Such an approach supports a conceptual model founded upon the work of Meeuwisse.7 Analysis of player movement patterns has enabled researchers to determine the physiological demands of such movement.52–54 Consequently, football can be viewed as an intermittent sport punctuated by bouts of repeated high intensity exercise.54
Investigating shear stability of Rugby Union natural turf pitches
2015, Procedia EngineeringThe relationship between ground conditions and injury: What level of evidence do we have?
2013, Journal of Science and Medicine in SportCitation Excerpt :Findings were comparable to the earlier study, with ground hardness not identified as a significant predictor of ACL injury.10 Recently, a study in community level Australian Rules footballers has considered the relationship between prospectively measured injury data and objectively measured ground hardness.9 Ground hardness was measured (using a 2.25 kg Clegg hammer dropped from 45 cm, with the first drop measure recorded) at nine locations on a subset of grounds over the 2007 and 2008 football seasons.
The risky side of sports participation
2013, Journal of Science and Medicine in Sport