Tackle characteristics differed between levels of play. The number of tacklers and the sequence of tackler contact with the ball carrier require consideration from an injury prevention perspective.

ObjectiveConcussion is a prevalent brain injury in sport and the wider community. Despite this, little research has been conducted investigating the dynamics of impacts to the unprotected human head and injury causation in vivo, in particular the roles of linear and angular head acceleration.SettingProfessional contact football in Australia.ParticipantsAdult male professional Australian rules football players participating in 30 games randomly selected from 103 games. Cases selected based on an observable head impact, no observable symptoms (eg, loss-of-consciousness and convulsions), no on-field medical management and no injury recorded at the time.Primary and secondary outcome measuresA data set for no-injury head impact cases comprising head impact locations and head impact dynamic parameters estimated through rigid body simulations using the MAthematical DYnamic MOdels (MADYMO) human facet model. This data set was compared to previously reported concussion case data.ResultsQualitative analysis showed that the head was more vulnerable to lateral impacts. Logistic regression analyses of head acceleration and velocity components revealed that angular acceleration of the head in the coronal plane had the strongest association with concussion; tentative tolerance levels of 1747 rad/s2 and 2296 rad/s2 were reported for a 50% and 75% likelihood of concussion, respectively. The mean maximum resultant angular accelerations for the concussion and no-injury cases were 7951 rad/s2 (SD 3562 rad/s2) and 4300 rad/s2 (SD 3657 rad/s2), respectively. Linear acceleration is currently used in the assessment of helmets and padded headgear. The 50% and 75% likelihood of concussion values for resultant linear head acceleration in this study were 65.1 and 88.5 g, respectively.ConclusionsAs hypothesised by Holbourn over 70 years ago, angular acceleration plays an important role in the pathomechanics of concussion, which has major ramifications in terms of helmet design and other efforts to prevent and manage concussion.

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These biomechanical results compare well with other studies. They should contribute to the identification of the energy levels at which concussive impacts occur in football for the purpose of a better evaluation of protective devices in these sports.

Concussion is a prevalent injury in collision and contact sports, but the biomechanics of concussion has mainly been assessed for helmeted head impacts. Concussion and no-injury cases had previously been reconstructed using rigid body simulations from a larger video database of unhelmeted head impact cases from Australian rules football, rugby union and rugby league. The KTH finite element human head model was used to simulate the 27 concussion and 13 no-injury cases, and the maximum principle strain levels in the corpus callosum were evaluated. The rotational kinematics and strain levels were compared to critical strain tolerance curves and reconstructed pedestrian impacts from the literature. It was found that the 5% critical strain tolerance curve equated to a maximum principal strain level of approximately 0.20 and was associated with concussive impacts involving prolonged loss of consciousness. The results suggest rotational kinematics above 4500 rad/s2 and 33 rad/s for peak resultant angular acceleration and maximum change in resultant angular velocity, respectively, as tentative tolerance levels for concussion involving prolonged loss of consciousness. Cases involving short duration or no loss of consciousness had similar rotational kinematics and strain levels in the corpus callosum, suggesting that these injuries are of similar severity. The findings support the hypothesis that sports concussions share some biomechanical characteristics with diffuse axonal injury