Feature Dr Jodi Richardson20

A SPATE of injuries to star players including Nick Riewoldt, Jonathan Brown and Shaun

Higgins has again raised the link between ground conditions and injury.

The Gabba and Etihad Stadium are the main grounds in question.

Teams travelling to the Gabba have complained about pulling up sore, and Hawthorn president Jeff Kennett recently labelled Etihad Stadium “Hammy Park”, referring to the injuries to Josh Gibson and Riewoldt.

The cause of injuries to AFL players is a longstanding issue in both sporting and academic circles.

Some football injuries are easily explained. For example, the momentum developed in the run-up at centre bounces was identified as the cause of posterior cruciate ligament (PCL) knee injuries in ruckmen.

The introduction of the 10m circle in 2005, limiting the run-up and thus the momentum of ruckmen, has reduced the incidence of these injuries dramatically.

Unfortunately, the answer is not usually this straight-forward and definitive causes for the high incidence of some injuries, such as hamstring strains, remain elusive.

Perhaps surprisingly, the link between AFL ground conditions and injury has been studied for more than a decade.

At the helm of this research is the co-author of the AFL injury report, former Sydney Swans team doctor and current team doctor for the Sydney Roosters NRL team Dr John Orchard.

Dr Orchard has conducted many

studies, some ongoing, into the relationships between ground hardness, rainfall, evaporation, season, grass type, shoe-surface traction, and injury in football.

Recently, with the hardness of the Gabba and Etihad Stadium in question, the AFL’s penetrometer readings have been more public.

The penetrometer is a device used to measure the ground hardness. It has a centimetre scale along its length and a 1kg weight attached which is raised to a height of one metre then released. The falling weight pushes a small shaft into the surface; the deeper the hole, the softer the surface.

The protocol for the testing requires that three drops of the penetrometer be performed at 20 locations on the ground the morning of the game.

The research does not show penetrometer readings for each ground, instead the values are averaged for all Victorian and northern grounds separately.

The published AFL penetrometer study conducted from 1997-2000 (571 AFL matches) found a trend towards a higher risk of anterior cruciate ligament (ACL) knee injury when the average of the penetrometer readings was less than 4.5cm.

The relative risk of anterior cruciate ligament (ACL) injury for players was found to be even greater when the average was less than 2.5cm (ie. even harder).

The study found that players had a higher risk of ACL injury when playing at the northern Australian (warmer) grounds and earlier in the season. As the season progressed, the

risk of ACL injury reduced.The latest injury report shows that a

club will have an average of eight players a week unavailable for selection due to injury – that’s a whopping 20 per cent off the roster each week!

The three injuries responsible for the most missed playing time are hamstring strains, ACL, and groin injuries.

ACL is the most severe common injury. Non-contact damage to this stabilising knee ligament most commonly occurs when landing from a jump when the knee joint is hyperextended (straightened beyond normal range) or when attempting a change in direction but the foot remains firmly planted in the turf and the knee joint twists.

Given that both mechanisms by which the ACL can be damaged involve the shoe-surface interaction, it is an ideal injury to research in relation to ground conditions.

Dr Orchard calculated a rate of over 40

ACL injuries per 1000 football matches at the beginning of the season (February to March). The rate of ACL injuries dropped to less than 20 injuries per 1000 matches from May to September.

Interestingly, and indeed pointing to a major influence on the occurrence of these injuries, was the finding that high rainfall and low water evaporation significantly lowered the risk of non-contact ACL injuries in footballers.

The higher incidence of lower limb injury early in the season and in drier or warmer areas in the AFL is mimicked in other sports played on natural grass and over similar seasons such as soccer, rugby and Gaelic football.

Dr Orchard’s research proposes that the factor synonymous with all of these sports most likely to influence non-contact lower limb injury and related to ground conditions is the traction between surface and boot.

High shoe to surface traction means

that once a boot is planted there is very little give in the ground, which can lead to a twisting of the knee depending on the movement of the player.

This is quite the opposite of what we saw at Etihad Stadium when Higgins damaged his ankle as the grass under his foot gave way, creating a huge divot in the playing surface.

The research shows that the harder and drier the ground, the more traction there is between the shoe and the surface. Shoe-surface traction is also higher with more grass cover and greater root density.

Dr Orchard’s research reveals that the likelihood of ACL injury is significantly reduced on grounds where the predominant grass species is perennial ryegrass, compared to Bermuda grass.

The shoe-surface traction on perennial ryegrass is generally lower than on other grasses due to less thatching (organic matter underneath the lawn) and fewer underground stems, both reducing the “grab” of the grass on the boot.

Dr Orchard has shown that grass type is a stronger predictor of ACL injury than weather, including rainfall, but weather conditions will influence grass type as ryegrass will predominate over Bermuda grass where rainfall is high and evaporation is low, as is the case in southern Australian grounds.

He proposed that the predominance of ryegrass as temperatures drop and rainfall increases, as well as reduced thatch and prevalence of underground stems due to wear over the course of a season, could be responsible for the decline in ACL injuries over a season, explaining the early-season bias.

However, the influence of player match fitness and conditioning early in the year could be a factor contributing to more injuries early in the season.

One factor that should be considered is the choice of football boots by players. Understandably, players will choose a boot that will give them the greatest speed and agility on the playing surface.

The more traction between the surface and the boot, the greater control the player has and the better his performance.

Research has shown that the number of cleats on boots, their length and their placement is associated with ACL injury.

The authors of this research found that players who wore boots with longer cleats at the edge of the sole of the boot with shorter cleats positioned in the middle of the boot, likely increasing shoe-surface traction, were at higher risk of an ACL tear.

When a player is weighing the choice between a boot for optimal performance versus one that may lower the risk of ACL injury, I am certain that the choice for performance will win every time.

Research into ground conditions and their influence on injury to AFL players is ongoing but there is a lot more to the equation than the hardness of the surface.

For years players and clubs have complained about Etihad Stadium surface being too hard as the ground is built over the underground car park, yet the injury to Higgins could arguably be related to the surface being too soft and giving way too readily.

Given that surface conditions are in many ways related to factors that cannot be controlled such as rainfall and evaporation, ultimately, there is only so much that can be done to minimise player risk.

InsIde Football Wednesday, June 30, 2010

GROUNDED!The science on AFL injuriesDoes the state of the ground cause injuries? Surprisingly, a great deal of research is done on the subject.

HAMSTRUNG: Nick Riewoldt succumbs at Etihad Stadium.

‘Dr Orchard has shown that grass type is a stronger predictor of ACL injury than weather conditions.’

ANOTHER ONE DOWN: Shaun

OUTSPOKEN: Jeff Kennett.