Injury rates in team sport events: tackling challenges in assessing exposure time

Determination of time at risk for game injuries in sports is best assessed with actual minutes of play per athlete. Since individual-level playing time is often unavailable, sports injury epidemiologists currently use one of two general methods to determine the amount of time athletes are exposed to risk during team sporting events. Some determine the amount of exposure time by counting only the number of athletes on the field during the game of the particular sport. This method closely replicates the results of the individual-level exposure time if studies have full team enrolment and games are played with a consistent number of players. Others in the field of sports injury surveillance use a method of applying a full unit of exposure time to every member of a team who plays in a game, however briefly, or to everyone on the game roster whether they play in the game or not. This latter method underestimates game injury rates (because it overestimates exposure time) with a magnitude related to the proportion of players on the field (ie, those at risk) divided by the number of players on the team who are considered to have participated. Recognising this is necessary to properly assess risk factors for injuries in team sport events, appropriately target injury prevention efforts and accurately combine studies using different methods in systematic reviews or meta-analyses. In epidemiology, incidence rate is calculated as the number of events divided by some unit of person time for a population at risk.1 In assessing injury rates during team sporting events, sports teams are dynamic cohorts where athletes are exposed to game-time injury risk only when on the playing field. Assuming no other problems with the study methodology, the unbiased …