Evidence for the aetiology of injuries in Australian football

Objectives-To determine in Australian football (a) the influence of ground hardness and playing grade (level) on game speed and structure, and (b) pla yer movement patterns throughout the game and across levels. Methods-The design consisted of several studies. Seventeen games played on grounds of different hardness in 2000 were used to determine game speed and structure. Four first grade and four second grade grand final games (1994, 1996, 1997, 1999) were used to determine the game speed and structure on t he same ground but at different levels. Fifty one players (44 first grade a nd seven second grade) were used to measure movement patterns within games and across levels during the 2000 season. Results-There was a significant relation between ground hardness and game s peed, which could lead to higher injury rates when the ground is harder. Th ere was a 6.7% difference in game speed between the first and second grade levels reflecting differences in injury incidence. The first grade games we re also characterised by a greater number of shorter, high intensity play p eriods and longer stop periods than the second grade games. Midfield player s in the first grade games covered about 24% greater distance than their se cond grade counterparts, and there was a significant difference in their pl aying speeds. Conclusions-Over the past 40 years, the game speed in the top level of Aust ralian football has approximately doubled. Over the same time, the number o f collisions and the estimated injury incidence have also doubled. This stu dy provides additional support to the suggestion that these variables are s trongly linked. Factors such as ground hardness, playing level, and time du ring the game influence game speed and are therefore important in injury de velopment in Australian football.