# Evaluation of Snowboarding Helmets in Mitigation of the Biomechanical Responses of Head Surrogate
## 1 Introduction  
Impact-induced traumatic brain injury (TBI) during sports is a public health concern [1]. The biomechanical response of the brain against impact (blunt impact) and its connection to mild traumatic brain injury or concussion in sports is sought [2, 3]. The roleof helmets in mitigating impact is also of interest [4; 5; 6]. Considerable progress [5; 6; 7; 8] has been made in recent years in measuring head kinematics with and without the helmets. For helmets used in American football, this has been conducted in the laboratory setting [9; 10; 11] as well as on the field using mouthguards [12; 13] and helmet-mounted sensors [14; 15; 16]. The measurements of head kinematics with bicycle and snowboarding helmets have been generally limited to laboratory measurements [17; 18; 19], mostly using a drop tower setup. Further, compared to the bicycle helmets [5; 6; 8; 20; 21], studies using snowboarding helmets [22; 23; 24] are extremely limited. A snowboarding helmet is different from a bicycle helmet in terms of the design of various subcomponents. For example, when compared to a snowboarding helmet, a 'comfort liner' is generally absent [22], the 'impact mitigation liner' area is smaller [25; 26], and the hardness of the helmet shell is lower in the bicycle helmet [25]. Even though head kinematics measures are useful, they do not provide direct information regarding the response of the brain or brain simulant. To the best of the authors' knowledge, there is only one study [8] in the literature that investigates the performance of a bicycle helmet in terms of the response of the brain. Such an investigation for snowboarding helmets is lacking. Further, experimentally measured brain or brain simulant pressures with snowboarding helmets are also not available. Head and brain injuries are prevalent in snowboarding sports, which typically occur due to snowboarding accidents such as collisions, falls, high jump, etc. [26]. In the classical literature [4; 27; 28; 29] on blunt impact [30; 31] and American football [32; 33], it has been shown that head and brain injuries occur due to linear and angular kinematics, respectively. It is known in the literature that linear kinematics govern brain pressure [34; 35], whereas angular kinematics govern the equivalent (von Mises) stress and maximum principal strain (MPS) [27; 36; 37]. Hence, it is necessary to investigate these aspects for the evaluation of snowboarding impact severity. However, the existing standards [18; 19] for snowboarding helmet evaluation are based only on linear acceleration. These standards recommend that linear acceleration should not exceed 250-300 g. These standards do not consider angular kinematics (i.e., angular velocity and angular acceleration) and associated brain responses (i.e., brain pressure, equivalent stress, MPS) in the snowboarding helmet testing evaluation protocol. Most snowboarding helmets that have been developed are designed to mitigate the linear motion of the head, typically termed conventional helmets [22; 23; 24]. These conventional helmets consist of expanded polystyrene foam (EPS) that provides damping upon impact and reduces linear acceleration. In many of the investigations [5; 22; 23; 24], the performance of conventional helmets has been evaluated. They reported that conventional helmets reduce linear acceleration significantly compared to no helmet. However, the role of conventional helmets in mitigating the rotational motion of the head [6; 8; 22] is marginal. Hence, there is a need to develop new helmet technologies to potentially mitigate the combined effect of the linear and angular motion of the head arising from snowboarding impact. Further, it is necessary to design new technologies to prevent mild TBI, which has shown to be deleterious due to the cumulative effects. In recent years, anti-rotational technologies [6; 20; 22; 38] that are based on allowing relative motion between the head and the helmet have been proposed.