Considerations for the performance requirements and technical specifications of soft-shell padded headgear

Transcription

1 Special Issue Article Considerations for the performance requirements and technical specifications of soft-shell padded headgear Proc IMechE Part P: J Sports Engineering and Technology 2016, Vol. 230(1) Ó IMechE 2015 Reprints and permissions: sagepub.co.uk/journalspermissions.nav DOI: / pip.sagepub.com Declan A Patton 1,2 and Andrew S McIntosh 1 Abstract Laboratory and epidemiological research in Australian football, rugby league and rugby union has demonstrated that commercially available soft-shell padded headgear is currently ineffective in reducing the risk of concussion. However, modified headgear studies have demonstrated that significant improvements in impact energy attenuation performance are possible with small design changes, such as increases in foam density and thickness. A literature review of the design, performance and use of headgear in Australian football, rugby league and rugby union was conducted. A total of 23 articles were identified using primary and secondary search strategies, which included epidemiological field studies, laboratory impact test studies and studies investigating the behaviours and attitudes of players. The results of the review were synthesised and used to identify injury reduction objectives and appropriate design criteria. The need for a headgear standard was identified and performance requirements were discussed, which drew upon human tolerance and sportsspecific head impact exposure data. Usability and behavioural issues, which require consideration during the design process, were also assessed. Keywords Australian football, biomechanics, concussion, head injury, headgear, injury prevention, protective equipment, rugby Date received: 2 February 2015; accepted: 7 October 2015 Introduction The original design criteria or injury risk management objectives for many sports helmets are unclear. Helmets may have been initially developed to prevent skull fractures and serious brain injury, concussion or merely superficial injury. Early headgear worn in American football and cycling was made from padded leather, which lacked a hard shell. Mid-last century, in order to prevent skull fracture and related brain injuries, hardshell helmets replaced leather helmets in American football. 1,2 There is a general consensus that hard-shell helmet designs have been successful in preventing skull fractures in American football; however, the effectiveness of such designs in reducing the risk of concussion is inconclusive. 3 5 In 1993, the International Rugby Football Board (IRFB) allowed the use of soft-shell padded helmets in rugby union to protect the scalp and ears from lacerations and abrasions, 6 which will hereinafter be referred to as headgear. The governing bodies for Australian football and rugby league have also allowed the use of headgear; however, there is no interest in introducing hard-shell helmets at any level. Headgear usage in rugby union reportedly ranges from 26% to 54%, 12% to 49% and 5% to 21% for junior, 7 11 collegiate 8,11,12 and senior 8,9,11,13 16 players, respectively; however, headgear has only gained limited acceptance by Australian football and ruby league 14 players. In Australian football and the rugby codes, the majority of head injuries are superficial lacerations and concussion, whereas skull fracture and more severe brain injuries are rare In Australian football, 1 Australian Centre for Research into the Injury in Sport and its Prevention (ACRISP), Federation University Australia, Ballarat, VIC, Australia 2 Faculty of Science, University of New South Wales, Sydney, NSW, Australia Corresponding author: Declan A Patton, Australian Centre for Research into Injury in Sport and its Prevention (ACRISP), Federation University Australia, School of Mines Campus, Lydiard Street South, Ballarat, VIC 3350, Australia. declan@unswalumni.com

2 30 Proc IMechE Part P: J Sports Engineering and Technology 230(1) concussions were found to constitute approximately 3.1% 3.6% of all injuries to senior players in competition 20,26 and occur at a rate of 5.6 per 1000 playerhours. 27 Several studies have reported concussion incidence rates for senior rugby league and union, 23,38 42 which range from 0.6 to 34.8 per 1000 player-hours. Laboratory and field 11,47,48 research has demonstrated that commercially available headgear is currently ineffective in reducing the risk of concussion; however, there is a possible role for headgear to prevent superficial head wounds. 11,16 In contrast to the developments that have occurred in helmet design for American football over the last decade, little has changed in the design and performance of headgear in other football codes 8,11,48,49 despite the incidence rates of concussion in Australian football and the rugby codes being greater than in American football. 39 For Australian football and the rugby codes, some of the issues affecting the development of headgear are cultural barriers, lack of product standards and playing laws. 44 The overarching aim of this study was to undertake a review of the relevant headgear literature pertaining to headgear in Australian football, rugby league and rugby union. The results of the review were synthesised and used to identify technical specifications and performance requirements for headgear in the context of (1) injury reduction objectives, (2) design criteria, (3) epidemiology data, (4) biomechanical head impact exposure data, (5) efficacy and effectiveness, (6) behavioural and usability factors and (7) current and potential standards and regulations. Literature review process Search strategy A literature review, using PubMed, was carried out to identify peer-reviewed articles investigating the design and performance of headgear, which have been published since The keyword search terms were a Boolean combination of headgear, rugby, football and soccer, for example, rugby AND headgear. Only English language peer-reviewed journal articles, conference proceedings, theses and books were considered. In addition to the primary PubMed database search, the strategy included a secondary search of the reference lists of identified sources for additional articles, which also satisfied the primary search selection criteria. Inclusion criteria Articles were identified for potential inclusion during two stages of primary assessment, title and abstract, followed by a full-text assessment during the secondary search of references with each article. Grey literature, which is unpublished academic literature, for example, technical reports, was also assessed by the authors during the secondary search; however, such literature was only included if rigorous research of a sufficient calibre Table 1. Search strategy summary. Search Level Articles Included Excluded Total Primary PubMed Title Abstract Full text 2 19 Secondary References 4 23 was reported, which did not duplicate the results of the published articles. Articles were eligible for inclusion if they investigated the design, performance or use of headgear. Review articles were not included; however, the full texts of such articles were obtained and included during the secondary search strategy. Articles investigating the design and performance of soccer headgear were only included if there was some content on headto-player or head-to-ground contact, whereas articles focusing exclusively on ball-to-head impacts were not included. Final literature set Initially, 52 articles were identified from the PubMed literature search (Table 1). During the title and abstract review stages, 16 and 15 articles were excluded, respectively. The full-text review stage excluded a further two articles. The secondary search strategy returned four articles for a total of 23 articles (Table 2): eight laboratory studies involving impact testing of headgear, 43 46,50 53 six epidemiological field studies investigating the effectiveness of headgear, 11,16,39,42,47,54 eight behavioural studies concerning the attitudes of players towards headgear 7 9,12,18,19,49,55 and one study involving a combination of behavioural and field study types. 48 A report from the Rugby Headgear Study was included as it provided valuable information, 49 which supplemented information reported by peer-reviewed articles from the same study. 7,44,47,56 Two soccer headgear articles were included, which contained data on player-to-player or player-to-ground contact. 53,55 One article involved American football; however, it also reported upon rugby headgear. 39 Injury reduction objectives for headgear McIntosh et al. 57 assessed the head injury risks in a range of sports, including soccer and rugby union, which was updated during the current review to include Australian football and rugby league (Table 3). Studies investigating injury incidence in unhelmeted contact football codes, that is, Australian football, 20,26,27 rugby league and rugby union, 23,38 42 have identified concussion as a commonly occurring head injury. Therefore, reducing the risk of concussion is an important aim of injury risk management strategies, for

3 Patton and McIntosh 31 Table 2. Summary of headgear literature.. Source Sport Type (level a ) Findings Finch et al. 7 Rugby union Behavioural Safety was the primary reason cited by players for wearing headgear. Players report that they are more confident and able to tackle harder if they wear headgear. Marshall et al. 8 Rugby union Behavioural A third of schoolboy players reported wearing headgear. Only 12% 18% of adult male players reported wearing headgear. Pettersen 9 Rugby union Behavioural Most players believed that headgear prevents concussions. Only 27% of players reported wearing headgear. A third of coaches did not believe that headgear prevent concussions. Finch et al. 18 Australian football Behavioural Almost all players (91%) reported not using headgear during the previous season and 80% of non-users reported they would wear it if it prevented concussions. Braham et al. 19 Australian football Behavioural Almost all players (98%) reported not wearing headgear during the previous season. Kahanov et al. 12 Rugby union Behavioural Approximately half of the players reported using headgear, 63% of whom believed that headgear often or sometimes reduced the number of concussions. McIntosh et al. 14, b Rugby union Behavioural Players perceived headgear as providing protection against injury. Delaney et al. 55 Soccer Behavioural Players with a history of concussion and female players were more likely to wear headgear. Headgear reduced the risk of concussion and scalp injuries. McIntosh et al. 48 Rugby union Behavioural, field (I) Standard headgear did not reduce the risk of concussion; however, a strong trend was observed with the use of modified headgear and a reduction in concussion. Braham et al. 54 Australian football Field (I) Headgear compliance was low for intervention arms rendering assessment of headgear effectiveness difficult. McIntosh and McCrory 47 Rugby union Field (II-1) Commercially available headgear did not provide significant protection against concussion in adolescent males. Marshall et al. 39, b American football, rugby union Field (II-3) A portion of the difference in injury rates between the two sports was due to differences in protective equipment regulations. Jones et al. 16 Rugby union Field (II-3) Headgear use was associated with substantial, but nonsignificant, reductions in superficial head and facial injuries. Marshall et al. 11 Rugby union Field (II-3) Headgear did not reduce the risk of concussion, but was associated with the prevention of scalp injuries. Hollis et al. 42 Rugby union Field (II-3) Players reportedly always wearing headgear during games were found to have a significantly reduced risk of concussion. McIntosh et al. 44 Rugby union Laboratory Commercially available headgear did not reduce the likelihood of concussion. McIntosh et al. 51 Rugby union Laboratory Modified headgear had significantly better impact energy attenuation performance compared to the standard model. Kenny 43, b Australian football Laboratory Commercially available headgear was not recommended as a total protector against head injuries. Hrysomallis 45 Australian football, rugby league, rugby union Laboratory Significant correlation between headgear thickness and HIC. Most commercially available headgear provided inadequate impact energy attenuation due to limited thickness. Knouse et al. 50 Rugby union Laboratory Energy attenuation performance of commercially available headgear decreased after repetitive impacts. McIntosh et al. 52 Rugby union Laboratory Modified headgear, with foam thickness of 16 mm, had significantly better impact energy attenuation than commercially available headgear. Withnall et al. 53 Soccer Laboratory For a risk of concussion just over 50%, mean change in head velocity was 4 m s 21. For head-to-head impact speeds of 2 5 m s 21, the presence of headgear reduced peak accelerations. Eager et al. 46, b Rugby union Laboratory Commercially available headgear did not reduce the likelihood of concussion. HIC: Head Injury Criteria. a Level refers to the quality of the study design. b Articles identified from secondary search strategy.

4 32 Proc IMechE Part P: J Sports Engineering and Technology 230(1) Table 3. Summary of head injury risks, based on McIntosh et al. 57 Sport Injury risk All head injuries Concussion Severe head injury Australian football Amateur: 10.0% of all injuries 26 Amateur: 3.1% of all injuries 26 Minimal Professional: per 1000 playerhours Rugby league Professional: 5.7% of all injuries 28 Amateur/semi-professional: 3.8% 4.8% of all injuries, 32, per 1000 player- Minimal hours 32,60 Professional: 3.5% 8.7% of all injuries; 12,13,28,29,61, per 1000 player-hours 28,29,33,62 Rugby union Amateur: 17.3% 18.6% of all injuries, 22,39 Amateur: 3.8% 4.7% of all 21.2 per 1000 player-hours 39 injuries, 22,23,39, per 1000 playerhours 23,39,42 Minimal Professional: 7.0% 25.1% of all injuries, 25,40, per 1000 player-hours 41 Professional: 2.1% 4.9% of all injuries, 25,40, per 1000 playerhours 40,41 Soccer Professional: 5.7% of all acute injuries, per 1000 player-hours per 1000 player-hours 64 Collegiate: 5.3% of all injuries, per American football Collegiate: 6.1% of all injuries, per Medium 1000 player-games player-games, per 1000 athletic-exposures 65,66 which headgear is one of a number of interventions that may be applied. Superficial injuries to the face and scalp are common in the rugby codes, constituting up to a third of all injuries, 20,22,23,25,29,38,63 due to frequent contact with opposing players and the ground during tackles. Such injuries are relatively uncommon in Australian football accounting for only 6% of all injuries. 20 In addition, it is known anecdotally that players are treated in back play or on the sidelines for superficial head injuries or continue to play without treatment. Therefore, a secondary objective should be to reduce the incidence of superficial head injuries. Severe head injuries are rare in Australian football and the rugby codes. 20,21,67 69 The Ontario study of Catastrophic Injuries in Sports and Recreation reported that 2.9% of all severe injuries in rugby were sustained to the head, 70 which was lower than basketball (30.0%), 71 baseball (26.1%), 72 soccer (15.8%) 73 and ice hockey (6.5%). 74 No severe head injuries in American football were reported during the Ontario study; 75 however, other studies have reported severe head injuries in high school and collegiate American football, 76,77 the incidence of which has risen in recent years. 77 No severe head injuries were reported during the Rugby Union Injury Surveillance Study, which was a prospective cohort study of school, club and elite players during the seasons. Similarly, no severe head injuries were reported during National Rugby League (NRL) Injury Surveillance Studies. 61,78 The Ontario study of Catastrophic Injuries in Sports and Recreation also reported that 11.8% of all catastrophic injuries in rugby were facial fractures, 70 which was lower than soccer (13.2%) and baseball (13.0%), but higher than ice hockey (5.6%), American football (2.0%) and basketball (0.0%). Other studies have reported that less than 3% of all injuries in rugby union are facial fractures ,40,63,79 84 Similarly, facial fractures constitute 4% and 1% 2% of all injuries in rugby union 85 and Australian football, 25,86 respectively. The incidence of facial fractures in Australian football and the rugby codes has been reported as less than 1.0 per 1000 player-hours. 34,40,41,58,86 Such values are comparable to soccer, for which facial fractures have an incidence of 0.4 per 1000 player-hours and represent 1.3% 2.5% of all injuries. 64,87 The low incidence of severe and catastrophic head injuries, such as subdural haematomas and skull fractures, in Australian football and the rugby codes supports the perspective that hard-shell helmets with face-masks are not needed and the prevention of such injuries is not of primary concern with regard to headgear design. In summary, the injury risk management objectives for headgear should be to reduce the incidence and severity of concussion and superficial head injuries. Design criteria for headgear The main purpose of headgear, as an injury risk management control, is to reduce the likelihood and severity of injury to the head, concussion in particular. 88 McIntosh and McCrory 44 stated that to function effectively, headgear must attenuate impact energy and thereby reduce head impact force. It was also stated that headgear must offer protection for multiple impacts within a game and over a playing season.

5 Patton and McIntosh 33 In a report to the New South Wales Sporting Injuries Committee, McIntosh et al. 14 identified additional headgear design considerations: load distribution, head coverage, retention system and surface properties. In helmets, load distribution is provided by the shell; however, headgear is also required to distribute impact loads and thereby reduce the likelihood and severity of superficial injuries, for example, scalp laceration. In consideration of injury mechanisms, injury risks and player acceptance, McIntosh et al. 14 concluded that the shape and retention system should cover areas of the head most prone and vulnerable to impact and allow the headgear to fit securely on the head, respectively. Coverage of the ears is also a consideration as headgear should prevent ear trauma, for example, cauliflower ears during rugby union scrums, without impairing the hearing ability of a player. In terms of surface properties, low friction and no projections were considered desirable for football headgear. Such properties are thought to reduce rotational forces on the head and thereby reduce the likelihood of concussion. McIntosh et al. 14 identified additional performance requirements of a more general nature: water-resistant, light-weight and durable. An early report from the National Health and Medical Research Council (NHMRC) stated that headgear should weigh no more than 0.08 kg; however, no supporting evidence was supplied. 89 Barnes et al. 90 identified non-performancerelated design criteria to overcome wearer resistance, which requires headgear to be compatible, comfortable, convenient, relatively inexpensive and aesthetically attractive. Finally, headgear should not introduce any new hazards. 91 Epidemiological efficacy and effectiveness headgear To date, the epidemiological evidence shows that the current headgear designs are not effective or efficacious in reducing the risk of concussion. McIntosh and McCrory 47 investigated the effectiveness of headgear in a prospective study of Australian under 15 rugby union players. The study consisted of a headgear group and a control group; however, no significant difference was found between the concussion rates from the two study arms. In a level II-3 field study, Marshall et al. 11 also found that headgear did not reduce the likelihood of concussion for club rugby union players in New Zealand. However, headgear was associated with the prevention of superficial head injuries, 11 which supported the substantial, but non-significant, findings of Jones et al. 16 In another level II-3 field study, Hollis et al. 42 found that rugby union players who selfreportedly always wore headgear during games were less likely to sustain a concussion. McIntosh et al. 48 carried out a cluster randomised controlled trial with a control arm and two intervention arms, which were supplied with standard and modified headgear. The level I evidence of McIntosh et al. 48 demonstrated that headgear was not efficacious in reducing the incidence or severity of concussion. In a compliance analysis, McIntosh et al. 48 observed a reduction of over half the likelihood of concussion for users of the modified headgear compared to non-users; however, the finding was non-significant. The modified headgear was constructed using foam of greater thickness and density than the foam used to construct standard headgear. The data did not reveal any issues related to risk compensation type effects, as there were no differences in the overall injury incidence rates based on headgear use. One main limitation was the low compliance rate of the modified headgear group. 48 Low compliance was also an issue in a study of community level Australian Football, 54 which rendered assessment of headgear effectiveness difficult. During both studies, 48,54 it was observed that players were reluctant to change their use of protective clothing, which resulted in some players electing to not wear assigned headgear and returning to the baseline condition of no headgear or, in the case of the modified headgear study, standard headgear. In summary, commercially available and currently used headgear is at best only fulfilling a secondary injury risk management objective, preventing superficial head injury, and not contributing to the reduction in concussion. Impact location and kinematics of concussion To design headgear that will protect against concussion, the mechanisms and tolerance levels of injury need to be established. McIntosh et al. 56 investigated the dynamics of concussion impacts in codes of collision football played in Australia using video analysis and identified the mean closing speed as 7.0 m s 21 (standard deviation: 2.5 m s 21 ) for 100 cases. Newman and colleagues also used video analysis to investigate concussion impacts in American football; however, a substantially higher mean closing speed of 9.9 m s 21 (standard deviation: 0.8 m s 21 ) was reported. Newman et al. 93 stated that it is not the closing speed, but rather the head impact kinematics, which causes concussion. McIntosh et al. 56 reported a mean change in linear head velocity of 4.0 m s 21 (standard deviation: 2.0 m s 21 ) and a mean head impact energy of 56 J. The 85th percentile values for mean change in linear head velocity and mean head impact energy were 6 m s 21 and 93 J, respectively. Withnall et al. 95 estimated the linear head velocity of head-to-head impacts in soccer for three cases involving minor head injuries: 1.3, 1.8 and 2.5 m s 21. In a subsequent study, Withnall et al. 53 used Head Impact Power (HIP) as a concussion injury criterion and reported that a change in linear head velocity of 4.0 m s 21 was associated with a 56% likelihood of concussion.

6 34 Proc IMechE Part P: J Sports Engineering and Technology 230(1) Table 4. Summary of kinematic tolerance levels for concussion in sports. Source(s) Method Sport Likelihood of concussion (%) Threshold Linear acceleration (g) Angular acceleration (rad s 22 ) Zhang et al. 103 Funk et al. 104 Rowson and Duma 99 Funk et al. 105 Rowson et al. 100 McIntosh et al. 106 Rousseau 107 Hybrid III ATD reconstructions Instrumented helmets Instrumented helmets Instrumented helmets Instrumented helmets Rigid body reconstructions Hybrid III ATD reconstructions Professional American football Collegiate American football Collegiate American football Collegiate American football Collegiate American football Professional Australian football, rugby league Professional ice hockey 1 5 Not reported 5 32 Not reported Not reported a a a Not reported Not reported Not reported Not reported Not reported Not reported Not reported 10 Not reported Not reported Not reported Not reported Not reported b c d e Not reported 2200 ATD: anthropomorphic test device. a Corrected values. b Impulse duration of 15 ms. c Impulse duration of 20 ms. d Impulse duration of 25 ms. e Impulse duration of 30 ms. Concussion impacts in Australian football and the rugby codes were mainly to the temporal region of the head, 56 constituting 60% in Australian football and 67% in the two rugby codes combined. In contrast, American football impacts to the front, top and back of the head have been associated with injury Patton et al. 101 reconstructed impacts from Australian football using the Royal Institute of Technology (KTH) Finite Element (FE) Human Head Model with the findings suggesting that temporal impacts direct angular kinematics in the coronal plane, which result in injurious strain levels in the brain. Therefore, it is vital that the temporal regions of the head are adequately protected by headgear used in Australian football and the rugby codes. The difficulties in establishing a valid concussion injury threshold have been previously discussed; 102 however, some studies have reported tentative kinematic tolerance limits for sports-related concussion (Table 4). Zhang et al. 103 analysed the American football head impact cases, which had been previously reconstructed by Newman and colleagues using Hybrid III anthropomorphic test devices (ATDs), and reported linear and angular acceleration values of 82 g and 5900 rad s 22 for a 50% likelihood of concussion, respectively. However, such values were criticised by Funk et al. 104 for being too conservative and biased towards injurious impacts. Funk et al. 104 analysed over 27,000 collegiate American football head impacts using instrumented helmets and concluded that 50%

7 Patton and McIntosh 35 likelihood values could not be reliably calculated due to sparse exposure data in that region and, therefore, proposed 10% likelihood of concussion values of 186 g and 10,387 rad s 22 for linear and angular acceleration, respectively. More recently, Rowson and colleagues 99,100 analysed over 300,000 head impacts, which were recorded in collegiate American football using instrumented helmets. Rowson and Duma 99 developed the Summation of Tests for the Analysis of Risk (STAR) equation to evaluate helmet performance by integrating head impact exposure and concussion risk. This new injury risk function closely matched the risk curve of Funk et al. 104 for low-risk values, that is, less than 10%, and indicated a linear acceleration value of approximately 200 g for a 50% likelihood of concussion. Funk et al. 105 optimised risk curves using the instrumented helmet data to provide a lower bound for concussion; however, it was clarified that the risk curves are likely to underestimate the true risk of concussion. Rowson et al. 100 also developed risk curves using rotational kinematics and reported angular acceleration values of 5821, 6383 and 6945 rad s 22 for a 25%, 50% and 75% likelihood of concussion, respectively. In addition to American football, concussion studies in other helmeted collision sports, for example, ice hockey, 107 and unhelmeted collision sports, for example, Australian football and rugby league, 106 have reported tentative kinematic tolerance limits for sportsrelated concussion. Rousseau 107 used a Hybrid III ATD to reconstruct head impacts in professional ice hockey and reported linear acceleration values for a 50% likelihood of concussion of 23, 15 and 7 g for impacts with impulse durations of 15, 20 and 25 ms, respectively. Rousseau 107 also reported angular acceleration values for a 50% likelihood of concussion of 9200, 6900, 4600 and 2200 rad s 22 for impacts with impulse durations of 15, 20, 25 and 30 ms, respectively. Using rigid body reconstructions of unhelmeted impacts in Australian football and rugby league, McIntosh et al. 106 reported linear and angular acceleration values of 65 g and 3958 rad s 22, respectively, which were associated with a 50% likelihood of concussion. McIntosh et al. 106 also reported linear and angular acceleration values associated with a 75% likelihood of concussion: 89 g and 6633 rad s 22, respectively. However, as with the risk curve developed by Zhang et al., 103 the values reported by Rousseau 107 and McIntosh et al. 106 may be biased towards concussion and considered conservative. Laboratory headgear impact tests McIntosh et al. 44 carried out a total of 78 single-impact drop tests onto a flat anvil of eight commercially available headgear using both a rigid and Hybrid III headforms. In addition to drop height, several other parameters were varied across the test matrix: size, impact site and temperature. It was found that all headgear designs assessed, which were representative of all models available at the time, had very limited ability to attenuate impacts. In addition, the foam in some models exhibited deformation hysteresis after repeated impacts. In similar studies, Knouse et al. 50 and Eager et al. 46 found that the energy attenuation performance of the headgear decreased with each successive impact. Eager et al. 46 concluded that headgear had limited effectiveness to reduce the likelihood of concussion. McIntosh et al. 52 investigated the potential of modified headgear designs, which involved impact tests on polyethylene foam samples and headgear prototypes. Increasing foam thickness was found to significantly lower the peak acceleration, but no significant differences were found between peak linear accelerations for foam densities of 50 and 67 kg m 23. During the second phase of the modified headgear study, 52 two prototype headgear designs were constructed with increased foam densities and thickness: 45 kg m 23 and 12.5 mm to 65 kg m 23 and 14 mm; 45 kg m 23 and 10 mm to 60 kg m 23 and 16 mm. For all test configurations, the modified headgear outperformed the standard headgear and it was concluded that small modifications to standard headgear designs can achieve large improvements in impact attenuation performance. The modified headgear, constructed using 16-mm-thick foam with a density of 60 kg m 23, was assessed in the randomised controlled trial of McIntosh et al. 48 Hrysomallis 45 tested seven commercially available headgear using the National Operating Committee on Standards for Athletic Equipment (NOCSAE) headform and drop system, which is used for the NOCSAE American football helmet standard. 108 The densities and thicknesses of the foams used in the headgear ranged from 38 to 87 kg m 23 and 8 to 15 mm, respectively. Foam thickness was found to be significantly associated with Head Injury Criteria (HIC) scores and it was concluded that the thickness of foam in headgear needs to be at least 15 mm to offer adequate protection, which was consistent with the observations of McIntosh et al. 52 In an early study, Kenny 43 suggested a maximum thickness of 38 mm for headgear, but added this would result in a very bulky headgear design comparable in thickness to full-face motorcycle helmets. 109 More recently, Eager et al. 46 recommended that the IRB considered increasing the maximum thickness from 10 to 20 mm and maximum foam density from 45 to 75 kg m 23. Behavioural and usability factors of headgear Marshall et al. 8 investigated the use of protective equipment in a cohort of rugby union players and found that a third of schoolboy players reported wearing headgear; however, only 12% 18% of adult male players reported wearing headgear. In contrast, very few Australian

8 36 Proc IMechE Part P: J Sports Engineering and Technology 230(1) football players use headgear; 18,19 however, 80% of non-users stated that they would wear headgear if it reduced the risk of concussion. 18 Therefore, there is a potential market for effective headgear and an expectation that can be met in Australian football. The Rugby Headgear Study 49 investigated the effectiveness of headgear in reducing injury in rugby union, during the 2002 and 2003 playing seasons. In each year of the 2-year study, participating players were invited to complete pre- and post-season attitude surveys. A total of 1414 players participated in the pre-season survey, 576 of which participated in the post-season survey. In the pre-season survey, 79% of respondents stated that they always or often wear protective equipment and 60% stated that they had worn headgear during the previous season. Players that had worn headgear in the previous season were asked to nominate, from a list, the two most important reasons for wearing headgear. The two most common reasons were I feel safer when I wear headgear and I don t want to get an injury, which were selected by 55% and 52% of respondents, respectively. However, only 17% of respondents selected that they liked to wear headgear as one of the two most important reasons. Players that wore headgear during the previous season were also asked to provide responses, using a 5-point Likert scale, 110 to questions regarding the effects of headgear on their performance and their beliefs regarding the benefits of wearing headgear. It was reported that 60% believed that headgear always or often prevented injury and 80% always or often felt safer wearing headgear, which supported findings from previous studies in rugby union. 7,12 The Rugby Headgear Study 49 found that two-thirds of headgear users believed that they could always or often play more confidently and 55% felt that they could tackle harder when wearing headgear. The attitudes of players that had used headgear in the previous season tended to change with age group. For example, older players reported having less confidence in the injury prevention potential of headgear. Half of the players that had used headgear in the previous season reported that headgear always or often made their head hotter; however, few reported headgear to be uncomfortable or heavy. The most important features that informed the choice of headgear were aesthetics, cost and safety performance information, which were selected by 52%, 35% and 28%, respectively. The beliefs of players, regarding the likelihood of a player being injured while wearing headgear, remained largely unchanged between the pre- and post-season surveys. However, there was a substantial change in players believing that they could tackle harder when wearing headgear. Across all age groups, there was a reduction in those strongly agreeing that they could tackle harder after a season wearing headgear. Therefore, exposure to impacts while wearing headgear may calibrate the behaviour and attitudes of a player. The conflicting attitudes and beliefs are puzzling with players wearing headgear to prevent injury; however, aesthetics and cost of headgear drive purchasing decisions. This finding suggests that headgear standards have an important role. If all headgear complied with valid standards, then players would be provided with headgear options with similar impact attenuation performance and risk management potential, regardless of cost or aesthetics. Current headgear standards The Australian Football League (AFL) 111 and NRL 112 have relatively subjective laws regarding protective equipment, which state that a player shall not wear during a match any protective equipment other than protective equipment approved by the controlling body and protective clothing may be worn provided it contains nothing of a rigid or dangerous nature, respectively. The IRB 113 outlines more specific design regulations in regard to headgear: no sandwich construction, specific zones of coverage, minimum horizontal and vertical peripheral vision clearances, maximum foam thickness of 10 mm (with 2 mm tolerance), maximum foam density of 45 kg m 23 (with 15 kg m 23 tolerance) and minimum chinstrap width. In addition to the design regulations, the IRB mandates certain performance requirements for retention system strength, retention system effectiveness and impact attenuation. The latter involves mounting the headgear on a rigid headform and performing drop tests from 300 mm for various configurations: a single impact to the crown region and double impacts to the forehead and temple regions. The impact attenuation performance requirement states that the peak acceleration of impacts delivered to test locations shall not be less than 200 g, which is in contrast to all performance-based standards for helmets. For example, equestrian 114 and cycling 115 helmets require peak impact acceleration to remain below a certain level, thereby limiting the impact force imparted to the head. The IRB states that the impact attenuation performance requirement is to prevent potential injury to the wearer or another player coming into contact with that headgear. 116 In contrast to the lack of headgear standards for collision sports commonly played in Australia, standards exist for American football 108 and ice hockey 117 helmets. The recently developed STAR evaluation system for American football helmets computes a single metric from a total of 24 drop tests from varying heights to the front, side, rear and top of American football helmets and is used to compare the relative protective performance of different models. 99 Potential headgear standard Laboratory and field 11,47,48 research in Australian football and the rugby codes has demonstrated that

9 Patton and McIntosh 37 commercially available and currently used headgear is ineffective in reducing the risk of concussion. Therefore, an established need exists for headgear technical specifications, which could be drafted into a standard or as part of game laws/regulations. With regard to impact performance, at least four main characteristics must be defined: (1) test type, for example, headform drop, linear impactor or pendulum; (2) test severity, for example, energy or velocity; (3) headform type, for example, rigid or deformable and (4) injury predictors and criteria, for example, linear acceleration and/or angular acceleration. Other characteristics may also be included: repeat impact performance, retention system and condition of the headgear, for example, hot or cold and dry or wet. Test type The common test rig used in standards testing is the free-fall drop rig, which includes two-wire, three-wire and linear rail configurations. In addition, some standards use linear impactors, which involve a shaft that is accelerated to a selected speed and impacted into a stationary helmeted headform, which is usually mounted on an ATD neck. Pendulum impactors have also been suggested as a more repeatable and cost-effective alternative to linear impactors. 118 Linear and pendulum impactors introduce additional issues, such as ATD neck biofidelity; however, both test types are able to assess oblique impacts. Although there is merit in including an oblique impact test, further evaluation is required. At present, headgear designs are typically constructed from a single homogenous type of foam; therefore, oblique tests may not assess any further unique properties of the headgear than linear drop tests. The advantages of including oblique tests would be to encourage innovation and to provide a more direct biomechanical assessment of concussion risk reduction through reduced rotational forces on the head. The contact interface plays an important role when conducting impact studies and/or developing helmet standards. For headform drop tests, the flat rigid anvil is the most simple and commonly used contact interface for helmet standards. The IRB headgear regulation requires impacts onto a flat rigid anvil; 113 however, the NOCSAE American football standard currently requires a flat rigid anvil to be covered with a 12.7 mm rubber pad. 108 The NOCSAE contact interface is also used for the STAR evaluation system for American football helmets. 99 An additional test using a linear impactor has been proposed for the NOCSAE American football standard. 108 Some linear impactor tests involve mounting a piece of protective equipment to the face of the impactor to replicate a particular impact scenario within a sport, for example, a shoulder pad to replicate body checking in ice hockey 107 or a boxing glove to replicate a punch in boxing. 119 Test severity From reconstruction studies of Australian football, rugby league, rugby union and soccer head impacts, 53,56,95 impact speeds of 3 4 m s 21 have been identified, which could be considered relevant for headgear impact tests and correspond to drop heights ranging from approximately 0.45 to 0.87 m. McIntosh and McCrory 44 tested commercially available headgear using a rigid headform from a height of 0.6 m, which corresponds to an impact speed of 3.4 m s 21, and reported peak headform accelerations of g. However, peak headform accelerations of g were reported when using a Hybrid III headform with the same headgear and test configurations. The two modified headgear designs tested by McIntosh et al. 52 were able to maintain peak headform acceleration below 90 and 140 g during lateral impacts from drop heights of 0.3 and 0.4 m, respectively. One of the modified headgear designs recorded a peak headform acceleration of 171 g during a 0.5-m lateral impact. The modified headgear was associated, although not significantly, with a reduction in concussions during on-field testing. 48 To reconstruct headto-head impacts in soccer, Withnall et al. 53 used Hybrid III head and neck systems and found that the peak headform accelerations ranged from 27 to 55 g and 69 to 106 g for impacts speeds of 3 to 4 m s 21, respectively, which were substantially lower than the values reported by McIntosh and McCrory 44 due to the influence of the Hybrid III neck. The STAR evaluation system for American football helmets involves incremental drop heights ranging from 0.30 to 1.52 m, which are associated with impact speeds ranging from 2.4 to 5.5 m s Peak linear acceleration results for a hypothetical American football helmet were used to demonstrate the STAR evaluation, which received a rating of and ranked in the not recommended category. Once a standard has been established, a similar evaluation system could be used for headgear in Australian football and the rugby codes. Headform type and contact interface There are several different headforms currently being used in impact studies and incorporated into helmet standards, with the most common being rigid, Hybrid III and NOCSAE headforms. Due to high repeatability, rigid headforms are used for the majority of helmet standards and are available in a range of sizes. Although not used in helmet standards, the Hybrid III headform is extensively used in impact injury research. McIntosh and McCrory 44 tested commercially available headgear using rigid and Hybrid III headforms. The substantial differences between the results were attributed to the 10 mm skin of the Hybrid III headform, which essentially doubled the thickness of energy-absorbing material surrounding the headform. Van Den Bosch et al. 120 investigated the role of the Hybrid III headform skin during 0.2 m drop tests and

10 38 Proc IMechE Part P: J Sports Engineering and Technology 230(1) reported a peak linear acceleration of 60 g, which was approximately half the value for a relatively stiffer rubber padding. The NOCSAE headform, 121 which is also referred to as the Hodgson-WSU headform, is thought to be more biofidelic than the Hybrid III headform. Cobb et al. 122 compared the geometry of the NOCSAE headform to that of the Hybrid III headform and found substantial differences in several regions considered important to helmet fit. Kendall et al. 123 compared the Hybrid III and NOCSAE headforms in drop tests up to m and found that both headforms demonstrated good reliability; however, significant differences were observed between the peak accelerations. The NOCSAE headform is currently used in the STAR evaluation system for American football helmets. 99 Injury predictors and criteria There currently exists no helmet standard that uses rotational kinematics as performance criteria, despite some oblique impact tests proposed, which is likely limiting novel technologies such as the innovative Multi-Directional Impact Protection System (MIPS). There is a plan for the STAR evaluation system for American football helmets to include rotational kinematics, 99,100 possibly as a combined metric with linear acceleration. 127 Instrumented helmet studies in American football have provided valuable data to establish risk curves and tolerance limits for head kinematics. 99,100,104,105 In contrast, unhelmeted sports such as Australian football and the rugby codes have been restricted to using video analysis 56 and rigid body reconstructions; 106 however, recent technologies in the form of instrumented mouthguards and skin patches may provide an opportunity for in vivo data to be collected in unhelmeted sports If such data were available, it would be possible to develop a headgear evaluation system, similar to the STAR evaluation system for American football helmets, 99 which relates on-field exposure to laboratory tests. However, if such an evaluation system was to be developed for headgear, it would be separate to technical specifications within a standard or game laws/regulations. The limitations of only using peak linear acceleration as an injury metric for concussion are well recognised; 5,97,98,106 however, it provides a general measure of impact head injury and is easily assessed with repeatable test rigs. Any initial headgear standard would require simple performance criteria that are able to be met and not ignored by manufacturers. Such a standard could be graded with two or three levels of performance and/or could be revised after a time to provide more challenging pass criteria. Other criteria Laboratory studies investigating the impact attenuation performance of headgear have found that such performance decreased with each successive impact due to hysteresis in the foam liner of the headgear. 44,46,50 To account for the design requirement of performance during repetitive impacts, headgear may be subjected to a set number of impacts over a set duration; however, the rate of testing must be based on the rate of head impact occurrence during games, which has yet to be clearly defined. The retention system commonly used in headgear is constructed using hook-and-loop fasteners. Although the performance of the retention system is important, it has not been demonstrated as a reason why the current headgear models are ineffective in preventing concussion or other head injuries. The retention system has also not been identified as a cause of misuse or injury. The conditions of the headgear during testing are an important consideration. Rowson and Duma 132 found that the average in-helmet temperature during an American football game was strongly correlated with ambient temperature. Therefore, it would be reasonable to perform standard testing of headgear at ambient temperature. The performance of headgear when it is wet has yet to be assessed; however, this may need to be investigated as Australian football and the rugby codes are able to be played in wet conditions. It has been established that for headgear to satisfy these performance requirements, mass, thickness and foam density of the current designs need to increase. 43,45,46,52 It is unusual to stipulate dimensions, such as mass and thickness, in a helmet standard; however, dimensional design criteria could be identified as informative notes within a standard. Conclusion Relevant literature pertaining to headgear was sourced using primary and secondary search strategies, which included epidemiological field studies, laboratory impact test studies and studies investigating the behaviours and attitudes of players. The results of the review were synthesised and used to identify injury reduction objectives and appropriate design criteria. The need for a headgear standard was identified and performance requirements were discussed, which drew upon human tolerance and sports-specific head impact exposure data. Usability and behavioural issues, which require consideration during the design process, were also discussed. Declaration of conflicting interests The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. Funding The authors disclosed receipt of the following financial support for the research, authorship, and/or

11 Patton and McIntosh 39 publication of this article: The Australian Centre for Research into Injury in Sport and its Prevention (ACRISP) is one of the International Research Centres for Prevention of Injury and Protection of Athlete Health supported by the International Olympic Committee (IOC). References 1. Levy ML, Ozgur BM, Berry C, et al. Analysis and evolution of head injury in football. Neurosurgery 2004; 55(3): Levy ML, Ozgur BM, Berry C, et al. Birth and evolution of the football helmet. Neurosurgery 2004; 55(3): Benson BW, Hamilton GM and Meeuwisse WH. Is protective equipment useful in preventing concussion? A systematic review of the literature. Brit J Sport Med 2009; 43(Suppl. 1): i56 i Benson BW, McIntosh AS, Maddocks D, et al. What are the most effective risk reduction strategies in sport concussion? From protective equipment to policy. Brit J Sport Med 2013; 47(5): Hoshizaki TB, Post A, Oeur RA, et al. Current and future concepts in helmet and sports injury prevention. J Neurosurg 2014; 75(4): s136 s International Rugby Football Board (IRFB). Laws of the game of rugby football. London, England: IRFB, Finch CF, McIntosh AS and McCrory PR. What do under 15 year old schoolboy rugby union players think about protective headgear? Brit J Sport Med 2001; 35(2): Marshall SW, Waller AE, Loomis DP, et al. Use of protective equipment in a cohort of rugby players. Med Sci Sport Exer 2001; 33(12): Pettersen JA. Does rugby headgear prevent concussion? Attitudes of Canadian players and coaches. Brit J Sport Med 2002; 36(1): Grobler C. The possible aetiologies for the incidence of rugby injuries among top level Gauteng rugby-playing schools. Master s Thesis, Technikon Witwatersrand, Johannesburg, South Africa, Marshall SW, Loomis DP, Waller AE, et al. Evaluation of protective equipment for the prevention of injuries in rugby union. Int J Epidemiol 2005; 34(1): Kahanov L, Dusa MJ, Wilkinson S, et al. Self-reported headgear use and concussions among collegiate men s rugby union players. Res Sports Med 2005; 13(2): Gerrard DF, Waller AE, Bird YN, et al. The New Zealand rugby injury and performance project: II. Previous injury experience of a rugby-playing cohort. Brit J Sport Med 1994; 28(4): McIntosh AS, McCrory PR, Comerford J, et al. Head injury and head protection in football. Report for the NSW Sporting Injuries Committee, School of Safety Science, University of New South Wales, Kensington, NSW, Australia, Holtzhausen LJ, Schwellnus MP, Jakoet I, et al. Pre-season assessments of South African players in the 1999 rugby Super 12 competition. S Afr Med J 2002; 9(2): Jones SJ, Lyons RA, Evans R, et al. Effectiveness of rugby headgear in preventing soft tissue injuries to the head: a case-control and video cohort study. Brit J Sport Med 2004; 38(2): Dicker G, McColl D and Sali A. The incidence and nature of Australian rules football injuries. Aust Fam Physician 1986; 15(4): Finch CF, McIntosh AS, McCrory PR, et al. A pilot study of the attitudes of Australian rules footballers towards protective headgear. J Sci Med Sport 2003; 6(4): Braham RA, Finch CF, McIntosh AS, et al. Community football players attitudes towards protective equipment: a pre-season measure. Brit J Sport Med 2004; 38(4): Seward HG, Orchard J, Hazard H, et al. Football injuries in Australia at the e lite level. Med J Australia 1993; 159(5): Gibbs NJ. Common rugby league injuries: recommendations for treatment and preventative measures. Sports Med 1994; 18(6): Hughes DC and Fricker PA. A prospective survey of injuries to first-grade rugby union players. Clin J Sport Med 1994; 4(4): Garraway WM and MacLeod DA. Epidemiology of rugby football injuries. Lancet 1995; 345(8963): McCrory PR. Neurological injuries in Australian and rugby football. In: Jordan BD, Tsaris P and Warren RF (eds) Sports Neurology. Philadelphia, PA: Lippincott- Raven, 1998, pp Bathgate A, Best JP, Craig G, et al. A prospective study of injuries to elite Australian rugby union players. Brit J Sport Med 2002; 36(4): Gabbe B, Finch CF, Wajsweiner H, et al. Australian football: injury profile at the community level. J Sci Med Sport 2002; 5(2): Makdissi M, McCrory PR, Ugoni A, et al. A prospective study of postconcussive outcomes after return to play in Australian football. Am J Neuroradiol 2009; 37(5): Gibbs NJ. Injuries in professional rugby league: a threeyear prospective study of the South Sydney Professional Rugby League Football Club. Am J Sports Med 1993; 21(5): Stephenson S, Gissane C and Jennings DC. Injury in rugby league: a four year prospective survey. Brit J Sport Med 1996; 30(4): Gabbett TJ. Incidence site nature of injuries in amateur rugby league over three consecutive seasons. Brit J Sport Med 2000; 34(2): Gabbett TJ. Incidence of injury in semi-professional rugby league players. Brit J Sport Med 2003; 37(1): Gabbett TJ. Influence of training and match intensity on injuries in rugby league. J Sports Sci 2004; 22(5): Hinton-Bayre AD, Geffen GM and Friis P. Presentation and mechanisms of concussion in professional rugby league football. J Sci Med Sport 2004; 7(3): Gabbett TJ. Influence of playing position on the site, nature, and cause of rugby league injuries. J Strength Cond Res 2005; 19(4): King DA, Gabbett TJ, Dreyer C, et al. Incidence of injuries in the New Zealand national rugby league sevens tournament. J Sci Med Sport 2006; 9(1 2):