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Legislative Assembly for the ACT: 1997 Week 13 Hansard (4 December) . . Page.. 4688 ..

6.1.2 Mechanisms of head inquiry

The mechanism of the production of an injury to the head is complex. It involves not only the effects of a direct impact on the skull and its coverings but, more importantly, the effects of the relative motion of the brain within the skull in response to that impact. This relative motion of the brain creates the shearing and rotational forces on the individual neurones which results in axonal stretching and diffuse brain injury (Holburn 1943; Gennerelli 1986). Shearing forces generated at impact may also directly disrupt the intracranial vascular tree resulting in haemorrhage. The direct impact to the skull vault or facial bones may result in fractures of these structures. Concussion differs from the more severe diffuse axonal injury in that it represents the mild end of the spectrum of head injury, where the symptoms are transient and the injury does not necessarily result in structural brain damage.

6.1.3 Helmet design

Helmets are designed to serve a number of functions. They absorb the force and decelerate the blow at the point of impact, resist impact-induced deformation, withstand surface abrasion and distribute the focal impact over a larger area. There is experimental evidence that cycling and ice hockey helmets achieve at least part of these aims (Ryan 1991; Mills 1990). There are additional data (Reid 1975) which suggest that United States (US) American football helmets are biomechanically efficient in laboratory testing in achieving these intended objectives.

In the US, catastrophic head and neck injuries have declined since the wearing of NOCSAE (National Operations Committee for Standards for Athletic Equipment) certified helmets in American football was made compulsory at all levels of play in the early 1970s (Torg 1982; Hodgson 1975). It is important to note, however, that other changes in the game such as rule changes (eg banning `spear' tackles - an impact with the vertex of the head) occurred at the same time and may explain the observed reduction in head injury rates.

The area of head-to-head impact experienced on the field of play is impossible to monitor via technology, at this point in time. Simulated head-to-head impacts however, in a laboratory setting, with cadaver and/ or anthropomorphic test dummy technology, indicate that low-level concussion, laceration and bruising occur at about 300 G. The use of soft head protection lowers the impact of a head-to-helmet contact by 10 to 35 per cent (270-195 G), depending on the product used (Morrison & Young 1993).

In situations where both heads are outfitted with soft head protectors, the reduction in impact is now decreased by 15 to 60 per cent (255-125 G), again product dependent (Morrison & Young 1993).

A great deal more research must occur in the area of repetitive impacts and the durability of products. The soft head protectors may have an opportunity to provide protection on repeated contacts without significant reduction in safety capacity. This work is yet to be performed (Morrison & Morrison 1994).

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