What causes brain injury in rugby?
Brain injury in rugby is primarily caused by forces transmitted to the brain during head impacts, especially rotational forces. Rotational forces cause the brain to rotate inside the skull. This is associated with tearing of tiny blood vessels and brain cells resulting, over time, in the breakdown of the blood-brain barrier and the creation of damaging neuro-inflammation. This is why brain protection in rugby needs to address more than cuts, abrasions, or external head contact alone.
Overview
The long – and short-term effects of head impacts in rugby league and union are becoming bigger talking points by the day. Brain injury is now beginning to be taken more seriously.
Red cards are on the rise as governing bodies try to reduce high tackles. This is in response to the increasing number of former players diagnosed with Chronic Traumatic Encephalopathy (CTE). Carl Hayman, Alix Popham, Michael Lipman, Steve Thompson, Neil Clarke, Tim Cowley, Jason Hobson, Neil Spence, Adam Hughes and Bobbie Goulding have all been diagnosed with CTE.
For a man in his 30s or early 40s, the odds of getting this diagnosis is around one in 10,000. And yet 75 former union players in England or Wales during the first 15 years of their professional era have now been diagnosed with CTE. This is roughly one in 20. And it is believed that up to one in two professional players will end up with some kind of neurological impairment.
Worryingly, the women’s players are beginning to echo the early years of men’s professionalism – bulking up and becoming fitter, faster and stronger. What does the future hold around brain injury in rugby?
This has all meant that contact guidelines, head injury assessment, law changes, lower tackle height, smart mouthguards, concussion education and management are now key talking points across rugby. Is brain trauma in rugby a recent problem, or has it simply been overlooked? It’s a combination of both.
In rugby, brain trauma has become overly focused on bigger impacts, concussion and contact load. However, it is the cumulative effect of smaller, sub-concussive impacts over time that contributes to neurodegenerative disease.
In both concussions and sub-concussions, rotational forces are present. So, there is a need to reduce rotational forces to the brain, as opposed to measuring and managing after an impact is received. Rotational forces occur from angled hits to the head, be it head-to-head, head-to-ball, head-to-hip or head-to-ground impacts. All of these cause the brain to rotate inside the skull, brain cells to shear, and fine blood vessels around the brain cells to be torn in a twist-like movement. This sets up abnormal inflammatory processes, which become harmful and trigger CTE.
Another confusion in the debate around brain trauma in rugby is that former players have CTE with young-onset dementia, and not dementia as is understood in the context of ageing. Dementia is an umbrella term, not a specific condition, and refers to a number of cognitive symptoms. A lack of understanding between CTE and dementia by the media, governing bodies, coaches, players and fans means that CTE is not being properly understood, nor the risk factors appreciated.
The most significant mitigation to reduce brain injury in rugby is reducing the transmission of rotational forces to the brain from concussion and sub-concussive impacts. Halos® headbands for concussions and sub-concussions are uniquely designed to lessen the risk of rotational forces to the brain.
Headguards (scrum caps) protect against surface-level wounds. They are “not intended nor expected to protect against any form of mild traumatic brain injury or skull fractures”. However, given that sub-concussions are 500 times more likely than concussions and are symptomless, players need headgear that will protect them from sub-concussions and neurological damage from rotational forces.
The risk of brain injury in rugby
In elite English rugby union, concussion rates have hit their highest levels since records began
In the 2022/23 season, the most common match injury sustained by professional rugby union players in England was a concussion, which had an incident rate of 18.4 per 1,000 hours of playtime. One thousand player hours equals 25 rugby union matches, excluding “extra time” .
An audit into the women’s game showed that concussion was the most commonly reported injury, making up 26% of all match injuries. Again, measured against 1,000 hours, the rate was 12.6, more than double the previous season – a rise put down, in part, to more consistent reporting and better identification of concussion.
Rugby league is even more dangerous because concussion occurs at a rate of 18 per 1,000 hours of game time in league [2]. This is one of the highest concussion rates of any sport, and that includes American football (15 per 1,000 hours of play).
The English governing bodies for both codes of rugby – the RFU and RFL – have introduced head injury protocols, but they focus on concussion. What they overlook is the number of repetitive, sub-concussive impacts which don’t produce overt signs or symptoms, but nonetheless cause damage to the brain.
How do head impacts injure our brain?
Concussion occurs when an impact to the head or body sends a strong force to the brain, resulting in significant, acute brain injury with symptoms including headache, mental fogginess, changes in memory, balance, coordination, behaviour, irritability, and slowed reaction time. Over 90% of concussions are not associated with a temporary loss of consciousness and more than 80% of concussions are diagnosed the next day or several days later.
Sub-concussions occur when the force of the impact damages brain cell function, but a player does not experience any symptoms and the impact is unnoticed. Repetitive, sub-concussive impacts cause injury to the fine blood vessels around the brain cells. This results in damage to the blood-brain barrier, a structure designed to protect the brain. When this structure is damaged by repetitive trauma, an abnormal mediated inflammatory response is triggered with the production of neurochemicals. The neurochemicals and inflammatory response should be protective. However, the problem arises when the brain is subjected to repetitive impacts before the protective neurochemicals and inflammatory changes from the initial head injury have had time to return to normal.
The subsequent, repetitive head injuries can then result in a further abnormally exaggerated production of neurochemicals, and an exaggerated inflammatory response which is harmful to the brain, rather than protective. This response damages the brain tissue and eventually leads to the irreversible death of brain cells. Over time, this abnormal inflammatory pathway, triggered by repeated head injuries in contact sports, leads to changes in a brain protein called tau.
The tau protein found within cognitive brain cells normally stabilises brain cells so they can work and communicate effectively with other cognitive brain cells. This allows an individual to think and behave normally. When the tau protein becomes damaged, it can no longer stabilise the brain cells and they lose their ability to function effectively. As the tau protein spreads around the brain, more and more brain cells – needed for thought and control of emotions and behaviour – are killed.
Rezon Halos®: Protecting Your Brain in Sport
Halos® is a groundbreaking sports headband that protects the brain. It’s the only headgear of its kind that is designed to reduce your risk of concussion and developing Chronic Traumatic Encephalopathy (CTE) from the accumulated damage of sub-concussions.
Why Halos®?
- Reduces concussion risk by 74%*
- Reduces rotational force to the brain by up to 61%, and linear force by up to 64%*
- Sleek, lightweight, flexible and hypoallergenic
- Water and tear-resistant
- Internationally recognised Virginia Tech 5 star safety rating
- The only CE/UKCA Category II PPE-certified protective headband – the UK and EU legal standard for protective headwear
*based on independent testing
As seen in
Limiting contact in training
The governing bodies for both codes of rugby – the RFU and RFL – have introduced head injury protocols, but they focus on concussion and not sub-concussions. World Rugby has introduced a framework which sets out non-mandatory contact guidelines for training sessions. It aims to inform coaches and players of the best practices for reducing injury risk and optimising match preparation.
These guidelines have been developed because training environments are much easier to control than competitive matches. They advise reducing the cumulative contact loads and time spent tackling in training to the lowest possible levels, reducing injury risk while still allowing for adequate player conditioning and technical preparation.
Reducing contact loading and the levels of physicality away from match days is one of the changes demanded by The Rugby Players Association (RPA). The group is made up of former players, and they are also in favour of incorporating data analysis into full-contact training.
The limits of measuring contact load
Repetitive head impacts during gameplay and training cause damage to the brain from concussion and sub-concussive impacts. The risk and severity of CTE is caused primarily by multiple smaller, sub-concussive impacts, and not by one-hit concussions. Sub-concussive impacts are those which are of sufficient force to adversely affect the function of the brain cells but do not cause symptoms of concussion. Players and those around them are not aware of these impacts. 20% of people with CTE diagnosed after life were recorded as never having sustained a single concussion.
There is no known safe threshold tolerance for rotational forces to the brain from concussion and sub-concussive impacts, or if there is a safe threshold of repetitive impacts in a game, season and career. Meaning, the focus should be on what level of brain trauma is too much, and why reducing rotational forces and protecting the brain from rotational forces from concussive and sub-concussive impacts is a smarter focus.
How are head injuries assessed during and after a match?
The Head Injury Assessments (HIA) Protocol has been developed for the elite level of rugby union to improve the pitch-side management of head injuries and concussion. HIA does not diagnose a concussion, it is a tool to help identify a suspected concussion.
HIAs take place when the referee, another match official or a pitch-side doctor sees a player take an impact to the head which may have caused a concussion, even if there are no immediately obvious symptoms. Instrumented mouthguards may also trigger an alert, calling for an HIA. It allows doctors to temporarily remove a player following a visible or potential head injury, where the diagnosis is unclear, to undertake an off-field assessment.
HIA is a three-stage process that consists of the following:
- Stage 1 – Game day, off-field assessment (when not showing clear on-pitch symptoms or signs, players must undergo an off-field assessment consisting of a clinical evaluation by an attending doctor who is aided by screening tools and video reviews. Players cannot return before 10 minutes to allow assessment to elapse. Players taken off for HIA can be replaced, and any replacement can take a kick).
- Stage 2 – Post-game, same–day assessment (after the match, every player entered into the HIA protocol must undergo another evaluation within three hours. This is done using a check of symptoms, memory assessment and balance evaluation – compared with previous player baselines).
- Stage 3 – 36-48-hour post-injury assessment (the player will be assessed again, going through a symptoms checklist, studying a player’s balance and using a cognitive assessment tool).
Players displaying obvious, on-pitch signs of concussion must be immediately and permanently removed from play, without further assessment.
HIAs in rugby league have free interchanges which allows for clubs with an HIA in place to deliver the medical attention required for possible concussive injuries, without having to use an interchange.
“Having CTE and knowing lots of small-force sub-concussions caused it. I’m determined my boys protect their brain and wear Rezon Halos® to protect them!”
Jason Hobson, former England Rugby Union player
The pitfalls of HIA and amateur rugby
HIAs have little utility because they are after-the-event interventions when brain trauma has already been incurred and the injury will continue to unfold.
There are no HIAs in amateur rugby union. If there is a suspicion that the player is confused or disorientated, they should be safely removed from the field for further assessment and should not return to play that day. If at any point during a match or training, a player is concussed or has a suspected concussion, that player must be immediately and permanently removed from the field of play. This is known as “recognise and remove”. Whether this is enforced in amateur rugby specifically is another question.
Physios in the professional and amateur game are relied upon to check the physical wellbeing of players. Unfortunately, there is not always one present in amateur rugby, just like there is not always trained medical staff and ambulance crews on hand in case of emergency. The responsibility for safeguarding players then falls on each individual club, while rugby’s governing bodies are seen more so as the overseers of the professional game.
This oversight means that amateur players, both in league and union, are much more likely to remain on the field after sustaining head trauma. In the absence of medical practitioners, and a higher likelihood of having fewer substitutes to replace them, players continue to put themselves in danger, unaware of the potential consequences.
Sideline testing and HIAs have flaws, false negatives, and little utility. This is why reducing rotational forces and protecting the brain from rotational forces from concussive and sub-concussive impacts through Halos® is a smarter focus.
Rugby League’s Response
The independent Board of the Rugby Football League have recently accepted 44 recommendations from the sport’s Brain Health and Clinical Advisory Group Sub-Committees, as the latest and most wide-ranging phase of the drive to make the sport safer and more accessible at all levels.
These included the following changes for the 2024 season:
- Mandated use of the latest models of Instrumented Mouthguards (iMGs) for players in Men’s and Women’s Super League.
- Mandated minimum off-season of four weeks, followed by an additional minimum two-week pre-season period without contact training, to reduce cumulative player load.
- Match limits over a 12-month period will be introduced, with different figures for forwards and backs to reflect their differing levels of contact exposure.
- Independent concussion spotters will be introduced on a trial basis in 2024.
- At all levels of Community Rugby League, and at Age Grade at professional clubs (including Reserve Grade), the legal limit for any contact is to be lowered – from shoulder height (i.e. below the neck) to armpit height (i.e. below the shoulder). Any contact above the armpit will therefore be penalised. It is further recommended that this Laws change should be applied at all levels of professional Rugby League from the 2025 season.
- Contact Rugby League replaced by touch / tag in a stepped approach, starting with Under 6s and 7s in the 2024 season, and continuing with that age group to Under 8s from 2025, and Under 9s from 2026.
- No Rugby League should be played in the month of December unless played as part of an existing winter offering – the latter including schools, colleges and student Rugby League.
Graduated return-to-play (GRTP) – how long is needed for the brain to recover?
When a player sustains a concussion, they enter into what is known as the Graduated Return To Play (GRTP) protocol. GRTP is a progressive program that brings an individual back to sport in a step-wise fashion. Under the GRTP protocol, the player can advance to the next stage only if there are no symptoms of concussion at rest, and at the level of physical activity achieved in the current GRTP stage.
GRTP is really an informed guess on how long it takes the brain to recover post-injury. Damage to the brain cells from an impact can be both immediate (damage to the brain cell structure) and delayed (blood flow changes or neural inflammation). Research and opinion from medical literature reviews suggest that 30 days is the minimum period before returning to play post a concussion event.
Under current GRTP Guidelines
- A player in elite rugby union can complete the six stages of the GRTP no earlier than the seventh day after injury, with the player’s return approved by an independent concussion consultant. Players with a history of concussion or who are removed from a match with obvious concussion symptoms will sit out from play for a minimum of 12 days.
- A player in amateur rugby union can complete the six stages of the GRTP in a minimum of 21 days for adults and 23 days for children.
- A player in rugby league can complete the six stages of the GRTP in a minimum of 11 days.
Despite females being more susceptible to concussion and sub-concussions, experiencing worse and more prolonged symptoms, there are no specific return to play guidelines for female players.
Rugby has focused on evaluating brain recovery based on the level of play. However, there is no precise answer to how long it takes the brain to recover post-injury.
Returning to play too soon can increase the risk of sustaining further injury and subsequent symptoms, requiring a prolonged period of recovery. Changes in white matter, brain connections and blood flow can persist a year or more after a concussion. Research [3] provides a significant association between a history of concussion and lower extremity injury, especially lateral ankle sprain, knee injuries and muscle strains. Athletes of all levels in sport have a greater risk of lower-body injury issues for more than a year following a sport-related concussion.
Specifically in professional male rugby union, research [4] has found that concussion elevated injury risk by 26%, increased the risk of head/neck, pelvic region and neurological injuries, and shortened the time to the next injury.
Having sustained a concussion in the current or previous season has been found to increase the odds of suffering another concussion by more than four-fold, based on research from professional male rugby union players competing at the highest level of rugby in England [5].
Currently in the game, about 15 per cent of the concussions we see happen after the game, or two days later at the HIA3 stage
Dr Éanna Falvey – Chief Medical Officer World Rugby.
Mainstream headwear doesn’t protect the brain
Head-worn protection in sport is typically considered in the form of helmets or headguards (scrum caps) in rugby.
Helmets are designed to protect the skull, not the brain. While a helmet effectively protects the skull from fractures, the brain instead receives the full force of the impact, resulting in concussion and sub-concussions.
Helmets are mostly tested against linear force reduction, not rotational forces. Ironically, helmets increase brain trauma by permitting more and heavier impacts to the brain.
Headguards (scrum caps) are not protective to the skull or the brain. They are only intended to protect against cuts and abrasions. World Rugby have designed the approval standard for headgear in a way that limits the full protection of players from brain trauma. Players are encouraged to protect themselves, rather than with safety equipment.
Headguards compliant with World Rugby regulation are not intended nor expected to protect against any form of concussion, sub-concussions or skull fractures. This explains why multiple studies [6] have illustrated that conventional headgear offers no statistically significant prevention or protection against concussion. Yet most players (82%), coaches (66%) and referees (64%) incorrectly believe protective equipment prevents concussion in rugby [7]. More concerningly, around a third of both club and school rugby players incorrectly believe that wearing a scrum cap/ headguard can prevent a player from getting CTE [8].
The design of a headguard (scrum cap) increases the risk of rotational forces to the brain. The gaps between the foam shapes create an uneven surface that allows for more rotational “catch points”, meaning more linear forces become rotational. Also, with a scrum cap design it closes or ties in the posterior portion of the head, meaning player vulnerability to impacts received to the back of the head and the occipital region of the brain.
Scrum caps have remained unchanged in their shape and design for over 100 years, before this neurological science was understood. The scrum cap design is fundamentally flawed in its inability to protect the brain from rotational injury. This is why Rezon would not use Rotection® technology in a headguard (scrum cap).
Technological solutions
Instrumented Mouthguards (iMGs)
From January 2024, iMG technology became part of the Head Injury Assessment (HIA) protocol in rugby union. No aspects of the HIA protocol were removed or replaced; instead, the introduction of iMGs is an additional safeguard.
iMGs measure and report head acceleration in real-time. They calculate the linear and rotational forces, location, direction, and number of head impacts. This data is fed to an online reporting portal and will provide in-game alerts to the independent pitch side medical team of when a player experiences a head acceleration event above the agreed threshold. This then informs the team medics/match officials that a player needs to be removed for an off-field HIA1 assessment.
iMGs that flash red to indicate players require a HIA will make their debut at the 2025 Women’s Rugby World Cup before being rolled out across the elite game. A light-emitting diode (LED) embedded in the mouthguard will flash red to alert on-pitch officials more quickly and raise awareness. Referees will stop play on sight of a flashing mouthguard and send the player for an assessment, rather than a pitch-side doctor waiting for a break to remove them. While the thresholds for rotational forces are the same for both male and female players at 4,500 rad/s², an acceleration alert is triggered at 75G (linear forces) for men and 65G (linear forces) for women.
iMGs do not:
- protect the brain;
- measure sub-concussions (below 5g);
- take account of a player’s individualised brain health (e.g. past brain injuries, tolerances of rotational forces, age, genetics, or medical history); or
- offer any clinical-meaningful conclusions from the data alone to provide elevated brain injury and/or CTE risk analysis.
The plan in future by World Rugby is for iMGs to be used in the community game, with ‘boil-and-bite’ versions of the gumsheld tech available.
Eye-tracking technology
Eye-tracking technology is also being introduced to help with the detection and management of concussion. Studies have suggested that oculomotor function (eye movement) alters at the time of a concussion or shortly afterwards. This includes blurred vision, difficulty reading, difficulty tracking a moving target, and problems scanning visual information. This technology is being piloted in matches alongside the HIA process and the return-to-play protocols. This technology does not reduce brain trauma, nor protect against concussion or sub-concussion. It is a measurement and management tool to identify concussion and is irrelevant to sub-concussion.
All of these technologies focus on measuring and managing brain injury after it has happened. Whilst removing a player with concussion is becoming accepted, removing a player based on cumulative sub-concussions is unlikely to be popular or practical when the player has no symptoms, and the numeric threshold has not been proven.
Measuring brain patterns
Measuring brain patterns through electroencephalogram (EEG) technology is also being introduced to better spot and manage concussion. EEG tracks and records brain wave patterns. EEG brain testing is typically used for tracking and observing brain state changes post brain injury. This technology can identify concussions but does not support preventative care. In our partnership with Cogwear, we have taken EEG to the next level by measuring clinical-grade EEG to provide unprecedented brain injury detection. Halos® Edge is the world’s first athletic wearable with clinical-grade EEG.
World Rugby Law 4 Headgear Trial
World Rugby has developed a trial process to enable the assessment of rugby headgear which, ‘according to the manufacturers have been designed to achieve specific, quantifiable medical purposes’ [9]. This specification uses World Rugby Regulation 12 (that headgear is not intended nor expected to protect against any form of mild traumatic brain injury or skull fractures) as a base specification with variations which do not increase the onerousness of the tests, or the requirements from Regulation 12. Given the position of the MHRA and EU Commission under the Borderline Manual [10], a rugby helmet cannot be considered as having ‘medical purposes’. The only product included in this linear acceleration-focused trial is N-Pro.
How does Rezon Halos® compare to N-Pro?
Rezon Halos® and the N-Pro headguard differ fundamentally in both design intent and independently verified performance. Rezon Halos® is specifically engineered to reduce rotational force transmission to the brain and holds an internationally recognised Virginia Tech 5-star safety rating, indicating a high level of protection against concussion risk [11].
By contrast, no scrum cap or rugby helmet, including the N-Pro headguard, has publicly disclosed a 4- or 5-star Virginia Tech safety rating. While N-Pro has undergone testing using the Virginia Tech head-to-head methodology, the same peer-reviewed testing framework used to assess Rezon Halos®, its star rating has not been made public. Results of N-Pro’s Virginia Tech head-to-head methodology testing are publicly available [12]. Overall, Rezon Halos® outperforms N-Pro.
N-Pro uses viscoelastic foam, to absorb and dissipate impact energy. While this approach is effective for surface impacts and linear forces, viscoelastic materials have limited influence on rotational forces, which are accepted to be the primary driver of brain injury. Independent testing shows that N-Pro reduces rotational forces by approximately 34%, whereas Rezon Halos® reduces rotational force transmission by at least 60%. This difference reflects a fundamental design distinction and brain protection intent: Rezon Halos® Rotection® Technology [13] is engineered specifically to address rotational mechanics, rather than relying primarily on linear energy absorption.
Virginia Tech is the leading independent biomechanics test laboratory for sports headgear. It evaluates products using a globally accepted, peer-reviewed methodology and assigns safety ratings from 1 to 5 stars. Only products achieving a 4- or 5-star rating are recommended. This testing programme has been operating for approximately 15 years and is based on more than two million recorded head impact data points.
Head Impact Testing Data from Virginia Tech
The Virginia Tech test measures rotational acceleration. Rotational acceleration is the measure of how quickly the head is rotating, and the unit of measure is radians per second squared (rad/s2).
Head impacts with less rotational acceleration produce less rotational forces to the brain. Rotational forces cause the brain to rotate, shearing brain cells, tearing fine blood vessels, and causing harmful brain inflammation.
Rotational brain injuries can occur thousands of times per season through concussive and sub-concussive impacts in rugby [14]. So, reducing rotational acceleration injuries in sport is incredibly important for the safety of players.
Across three impact speeds (7.2 km/h, 10.8 km/h, and 14.4 km/h) and two impact areas (side and back), Rezon Halos® outperforms N-Pro by achieving lower rotational acceleration results.
The three test graphs below show rotational acceleration when:
- wearing no head protection
- wearing N-Pro rugby headguard
- wearing Rezon Halos® brain protection.
At every test speed and impact location, Rezon Halos® achieves a lower rotational acceleration than N-Pro.
Reduction in rotational acceleration when experiencing a head impact at 7.2km/h
Side of head impact
Back of head impact
At this speed, Rezon reduces rotational acceleration to the side of the head more than N-pro, and significantly reduces rotational acceleration to the back of the head more than N-pro.
Reduction in rotational acceleration when experiencing a head impact at 10.8km/h
Side of head impact
Back of head impact
At this speed, Rezon reduces rotational acceleration at the side of the head compared to N-pro and significantly reduces rotational acceleration to the back of the head more than N-pro.
Reduction in rotational acceleration when experiencing a head impact at 14.4km/h
Side of head impact
Back of head impact
Test speed is key as, in rugby, collisions occur at more than 14.4 km/hr [15]. At this speed, Rezon outperforms N-pro with the greatest rotational acceleration reduction margins.
Rezon’s answer to brain trauma in rugby
The brain is at risk, not just to a single or high-force impact, but also to the multiple sub-concussive impacts which are invariably unnoticed and undetected in rugby. Every single impact on the head in training and playing has the potential to be career-ending and life-changing.
Whilst the effects of brain injury may be instantly visible, repetitive brain injury over many years may not be recognised until later, meaning it is never too early to protect the brain in sport. The way head injuries are dealt with in rugby is now an overwhelming priority. World Rugby, the Rugby Football Union, Welsh Rugby Union, and Rugby League are all facing a lawsuit from retired players who have been diagnosed with CTE.
The most significant mitigation to reduce brain injury in rugby is reducing the transmission of rotational forces to the brain from concussion and sub-concussions. Halos® is uniquely and intentionally designed to lessen the risk of rotational brain injury due to the reduction in the transmission of rotational forces to the brain from concussive and sub-concussive impacts.
Insights
Our insights provide focused, hard-hitting, five-minute articles from Rezon, giving more informed insights regarding brain injury in rugby.
- RugbySafe Research, englandrugby.com.
- How Dangerous is Rugby League?, fluentrugby.com.
- The Influence of Sport-Related Concussion on Lower Extremity Injury Risk: A Review of Current Return-to-Play Practices and Clinical Implications, Jason M. Avedesian, Tracey Covassin & Janet S. Dufek, 2020.
- Concussion increases within-player injury risk in male professional rugby union, Moore IS, Bitchell CL, Vicary D, et al, 2022.
- Padded Headgear does not Reduce the Incidence of Match Concussions in Professional Men’s Rugby Union: A Case-control Study of 417 Cases, Stokes K, Williams S, McKay C, West S, Roberts S, Tannhauser Sant’Anna R, Kemp SPT, Hagel B & Cross M, 2021.
- Rugby headgear and concussion prevention: misconceptions could increase aggressive play, Menger R, Menger A, & Nanda A, 2016.
- Concussed or Not? An Assessment of Concussion Experience and Knowledge Within Elite and Semiprofessional Rugby Union, Mathema P, Evans D, Moore IS, Ranson C, Martin R, 2016.
- Knowledge and attitudes of concussion and chronic traumatic encephalopathy amongst a sample of non-professional rugby players, Moore J & Deasy C, 2025
- World Rugby Law 4 Headgear Trial, World Rugby.
- Manual on Borderline and Classification in the Community Regulatory Framework for Medical Devices, 2019.
- Virginia Tech Helmet Ratings – Rezon Halos®.
- New generation of headgear for rugby: impact reduction of linear and rotational forces by a viscoelastic material-based rugby head guard, Ganly M & McMahon JM, 2018.
- Rezon Halos® Rotection® Technology. Rezon.
- Epidemiology of Head Injuries Focusing on Concussions in Team Contact Sports: A Systematic Review, Prien A, Grafe A, Rössler R, Junge A & Verhagen E, 2018.
- Efficacy of Rugby Headgear in Attenuating Repetitive Linear Impact Forces, Knouse CL, Gould TE, Caswell SV & Deivert RG, 2003.
