ABSTRACT
Combatants wearing rudimentary head protection have been depicted in drawings for thousands of years (Hoshizaki and Brien, 2004). While sometimes dramatic in appearance, the effectiveness of these helmets is not well documented; however, they likely provided some protection against impacts from falling to the ground and strikes to the head. In the early twentieth century, motorized travel became more common followed by increases in accidental head injuries. During the same period, recreational sports were becoming popular, also resulting in a higher incidence of head injuries. This increase in head injuries prompted an increase in research designed to measure the effectiveness of helmets. Helmets have been used for decades to reduce the severity and incidence of brain injury during both sporting and non-sporting events. They have been used for military purposes to prevent injury from bullets and shrapnel and in sport to prevent traumatic brain injuries, which often led to death or permanent disability (Hoshizaki and Brien, 2004). Originally, American football players used cloth followed by leather helmets to protect their heads, with subsequent injuries often severe. Over time, as manufacturing capabilities and standards of performance for helmets became more sophisticated, traumatic brain injuries became rare in sport. However, while the incidence of traumatic brain injury in sports such as football, hockey and lacrosse has been reduced through the use of helmets, the incidence of concussion remains high (Casson et al., 2010; Wennberg and Tator, 2003). This is, in part, a result of the method in which helmets are evaluated and subsequently designed (Post et al., 2012, 2013). Currently, helmet performance and certification primarily employs linear acceleration to predict the risk of head injury (Canadian Standard Association (CSA), 2009; National Operating Committee on Standards for Athletic Equipment (NOCSAE), 1998; Snell Memorial Foundation (SNELL), 1995). Linear acceleration is more closely associated with the risk of traumatic brain injury (Gurdjian et al., 1966; Thomas et al., 1966). Research has confirmed that while linear acceleration is effective for the evaluation of helmet performance for the reduction of traumatic brain injuries, it may not be suitable for evaluation of helmets with respect to managing the risk of concussive injury (Gennarelli et al., 1971, 1972; Holbourn, 1943; Hoshizaki et al., 2012; Kendall et al., 2012; Post et al., 2012, 2013). Sport activities with increased risk for traumatic head injuries such as cycling, motorsport and competitive alpine skiing do benefit from what are generally termed crash helmets designed to manage high energy impacts and protect against traumatic brain injuries. These helmets are designed and certified using peak linear acceleration as a measure of performance (Hoshizaki and Brien, 2004).
