Impacts to the back of the head can generate particularly high rotational acceleration and substantial brain-tissue strain [1, 2, 3, 4]. The posterior, or occipital, region therefore deserves effective protection. Most conventional headguards and scrum caps instead treat this area as a convenient location for fastening or adjusting sports headgear, leaving this critical area without adequate protection [5].
When we think about sports head protection, it is easy to focus on what can be seen from the outside. How thick is the padding? How much of the head does it cover? Will it reduce the risk of a cut, bruise or abrasion? Those questions do not tell us what happens to the brain during a head impact.
The brain has a jelly-like consistency and sits within a hard-cased skull. An impact on the head will involve both linear forces and rotational forces. Rotational forces are most significant for brain injury in sport, because angled forces cause the brain to rotate inside the skull, brain cells to shear, fine blood vessels in the brain to be torn, and the protective blood-brain barrier to be disrupted [6, 7, 10]. This results in an abnormal and harmful uncontrolled inflammation which damages the brain and increases the risk of longer-term neurodegenerative consequences including Chronic Traumatic Encephalopathy (CTE) [8, 9].
The transmission of rotational forces to the brain is the primary consideration for reducing concussion risk and protecting the brain from the cumulative damage of sub-concussions in sport. This is especially important for impacts at the back of the head because these impacts generate particularly high rotational acceleration [1, 2, 3, 4].
Why is Protecting the Back of the Head Particularly Important?
The occipital region refers to the posterior, or back, of the head. What makes this region particularly important for brain protection is the biomechanics of what can happen when it is struck.
Impact location is one of the largest factors associated with differences in impact magnitude, and research has repeatedly highlighted the importance of protecting the back of the head. A study of head impacts in American football found that rotational acceleration was greatest for impacts to the front and back of the head [1]. Laboratory work also found that angular accelerations were up to 30% higher in rear and lateral impacts than in frontal impacts [2]. A study of head-impact data from high-school and collegiate football players also found that when tissue response was grouped by impact location, the highest cerebral stress and strain measures were associated with impacts to the back of the head [3].
The important conclusion is that posterior impacts are capable of transmitting substantial rotational forces to the brain, resulting in brain deformation. The back of the head therefore needs to be treated as a high-priority region in protective design [1,2, 3, 4]. Most conventional head protection uses this area as a convenient location of fastening and lacing, rather than treating it as a priority area to protect [5].
How exposed is the occipital region across sport?
Posterior impacts are not a rugby-specific problem.
Anywhere an athlete can collide with another player, fall backwards or be struck by a ball or other object, the back of the head is an important area to protect.
In rugby and football, this can happen during player-to-player contact or when the head strikes the ground. In hockey, cricket and baseball, the posterior head may also be exposed to projectile impacts. Sports played on hard or low-friction surfaces create another mechanism; athletes can lose their balance and fall backwards onto a court or ice.
A Canadian study of recreational curling injuries found that more than 90% of acute injuries resulted from falls, while 31.7% involved head impacts. The researchers described backwards falls resulting in head injury as a characteristic mechanism and specifically raised the importance of brain injury within the sport [23].
Figure skating has different movement demands but shares the fundamental exposure created by falling on ice. A review of figure-skating injuries documented acute injuries across skating disciplines, with concussion and head injury among the recognised injury patterns [24].
The sports are different. The underlying principle is the same.
A backwards fall, posterior collision or oblique rear impact can rapidly accelerate and rotate the head. What matters to the brain is the mechanical loading that follows, not what sport you are playing, or at what level.
Watch: Curler, Rob Packham, talks about his curling accident and why he wears Halos®.
Why rotational acceleration matters to the brain
To understand why posterior impacts matter so much, we need to distinguish between two mechanics of head movement.
Both are relevant to head impact biomechanics. But brain tissue is particularly sensitive to rotational movement because of the way it deforms.
Brain tissue is far more resistant to compression than to deformation shear. When the head rotates rapidly, different regions of the brain can move relative to one another; this creates shear strains through soft neural tissue [6].
In simulations, oblique impacts that generated rotational as well as linear movement produced much greater brain strain than comparable perpendicular impacts [6].
In order to protect the brain from head impacts in sport, rotational force reduction needs to be the focus.
Conventional scrum caps and headguards are designed to reduce impact forces or linear forces with the goal of protecting the scalp from cuts and abrasions [19]. This is not the same as brain protection.
Any serious discussion about brain protection, sub-concussion and concussion risk reduction cannot consider linear force alone.
Head Protection vs Brain Protection
Traditional sports headgear and brain protection are not the same thing [11].
| Head Protection | Brain Protection |
|---|---|
| Designed to reduce cuts, abrasions and surface injuries | Designed to reduce brain injury risk |
| Typically focuses on reducing linear impact forces | Reduces linear forces and, more importantly, rotational forces, the primary driver of brain injury |
| Typically uses foam padding | Uses advanced protective technology engineered for brain safety |
| Protects the surface of the head | Designed specifically to protect the brain |
| Traditional all-head coverage sports headgear | Modern brain protection technology |
For the occipital region, the distinction has two implications.
First, coverage matters. If there is no, or reduced, protective material over an impact location, that part of the protective system cannot act directly at the point of contact.
Second, the protection must reduce the transmission of rotational force [6, 10]. Conventional foam padding has limited, if any, ability to reduce the transmission of rotational forces [11, 19].
Head protection and brain protection are designed to address fundamentally different injury and protective mechanisms.
The design problem with conventional rear-laced scrum caps
Rugby provides a particularly useful case study because the back of the head has traditionally been used as part of the fitting architecture of soft headgear.
Conventional scrum caps, including those manufactured by N-Pro, Canterbury, Body Armour, Optimum, Gilbert and Rhino, use a lace-up or adjustment system at the posterior head. That means the coverage is interrupted at the point where the two rear sections are brought together.
Concern about that architecture is not new.
More than two decades ago, Knouse and colleagues studied the impact attenuation of two types of International Rugby Board-approved rugby headgear. The researchers specifically drew attention to the posterior lace-up design in the occipital region [5].
Even when the tested headguards were correctly fitted, the opening between the two posterior sections measured approximately 1.7 cm to 2.0 cm, depending on the model [5].
The occipital impact site also produced significantly higher peak linear acceleration and Gadd Severity Index measurements than the parietal-lateral site for both tested headgear designs. The authors concluded that decreased attenuation in the occipital region warranted further investigation and that the design should be modified to improve protection there [5].
That finding is particularly relevant when read alongside the wider biomechanics literature.
We now have evidence that posterior impacts can generate high rotational acceleration and substantial brain strain [1, 2, 3, 4]. We also have peer-reviewed rugby-headgear research identifying an interruption in protective material and poorer attenuation at the posterior lace-up site [5].
Concern about rear-laced occipital coverage has existed in the peer-reviewed rugby-headgear literature for more than two decades.
Why ponytails can make the posterior coverage gap larger
Rear lacing can create an additional practical problem for athletes who wear a ponytail through the back of a scrum cap. The issue is what has to happen to the headguard to accommodate different hairstyles.
Posterior gaps exist even when the traditional laced headgear is fitted correctly [5]. If the architecture then has to be opened further to accommodate a hairstyle, the coverage issue can become more pronounced. A wider rear opening means less protective material over that part of the back of the head.
This is an equipment-design issue, not a hair issue. And it is one of particular importance for women in sport. Female sports players are more susceptible to concussion and can take longer to recover [12]. That a rear-laced scrum cap is potentially less protective for predominantly female hairstyles is particularly relevant for women and girls in sport.
Protective systems should accommodate real athletes, including different hair types and hairstyles, without asking them to create a larger gap through an important protective region.
How Rezon Halos® Was Designed to Protect the Back of the Head
Rezon Halos® takes a different approach to posterior coverage. The broader section of Halos® is designed to sit across the back of the head. Hair can also be worn above the headband and there is a rear drop that can accommodate a ponytail without reducing coverage [13].
This means different hairstyles can be accommodated around the protective system rather than by widening an opening through the centre of it.
Halos® offers complete 360º protection as there is no traditional lace-up gap running through the middle of the posterior protective section. In contrast to scrum caps which leave part of the posterior uncovered, Rezon Halos® has greater protective coverage in this critical area.
But most importantly, Rezon also protects the occipital region with brain protection technology that was actually designed to protect the brain. This contrasts with padded materials used to make scrum caps, which are intended only to reduce the risk of cuts and abrasions.
Halos® uses patented Rotection® technology, a system of nine independent protective layers designed to move relative to one another and reduce the transmission of rotational and linear force during head impacts. [14].
That combination is critical. The broader posterior section is intended to maintain protective material across the back of the head; Rotection® is designed to reduce the rotational transmission of rotational forces to the brain.
What does rear-impact testing show?
Rezon Halos® has undergone head-to-head testing using the Virginia Tech Soccer STAR methodology. Rezon Halos® achieved the highest possible 5-star rating from Virginia Tech and was shown to reduce rotational force transmission by up to 61% and linear force transmission by up to 64% [15, 16].
The significance of the posterior design becomes clearer when those results are compared with another rugby headguard.
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 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 head acceleration events can occur thousands of times per season through concussive and sub-concussive impacts in rugby [18]. So, reducing rotational acceleration injuries in sport is incredibly important for the safety of players.
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 7.2 km/h
Side of Head Impact
Back of Head Impact
At 7.2 km/h, 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 10.8 km/h
Side of Head Impact
Back of Head Impact
At 10.8 km/h, 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 14.4 km/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 [17]. At 14.4 km/h, Rezon outperforms N-Pro with the greatest rotational acceleration reduction margins. Across tested speeds, the faster the impact, the more pronounced the difference between N-Pro and Rezon Halos® rotational force capabilities becomes.
Rezon Halos® is rated 5-stars by the Virginia Tech Helmet Lab [15, 16]. Neither N-Pro nor any World Rugby-approved scrum cap have publicly declared a 4- or 5-star rating from Virginia Tech.
The difference between a scrum cap and Rezon Halos® brain protection
The fundamental distinction between brain protection and a conventional scrum cap is about what the equipment is designed to do.
World Rugby is explicit about the intended purpose of conventional headgear. Its current Headgear Performance Specification states that the injuries headgear is intended to protect against are cuts and abrasions. It further states that such headgear, which has limited impact-acceleration attenuation properties, is not intended or expected to protect against mild traumatic brain injury [19].
A conventional scrum cap is fundamentally head protection, developed within a specification centred on protecting the external head from cuts and abrasions [19, 20].
Rezon Halos® has a different design objective. It is brain protection, designed specifically around reducing the transmission of linear and, importantly, rotational forces associated with brain-injury biomechanics [14, 15, 16].
Why parents and players are choosing Rezon Halos®
Rezon Halos® is brain protection for sport.
Its purpose is to reduce the transmission of forces associated with the biomechanics of brain injury in concussive and sub-concussive head impacts, and reduce the accumulated damage from sub-concussions.
Rezon Halos® uses patented Rotection® technology and has been independently tested using Virginia Tech methodology.
Why Choose Halos®:
- reduces rotational force transmission by up to 61%;
- reduces linear force transmission by up to 64%;
- reduces concussion risk by 74%;
- achieved a Virginia Tech 5-star safety rating;
- holds CE and UKCA Category II PPE certification;
- is the only non-helmeted head-worn protection to combine CE/UKCA Category II PPE certification with a Virginia Tech 5-star safety rating [15, 16].
This combination matters because the future of sports head protection is not only about padding the outside of the head. It is about protecting the brain by reducing the forces transmitted to the brain and the accumulated damage from sub-concussions.
“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
- Magnitude of Head Impact Exposures in Individual Collegiate Football Players. Crisco JJ, Wilcox BJ, Machan JT, et al. Journal of Applied Biomechanics. 2012.
- The effect of impact location on brain strain. Tiernan S, Byrne G. Brain Injury. 2019.
- Estimated Brain Tissue Response Following Impacts Associated With and Without Diagnosed Concussion. Beckwith JG, Zhao W, Ji S, et al. Annals of Biomedical Engineering. 2018.
- Brain tissue strains vary with head impact location: A possible explanation for increased concussion risk in struck versus striking football players. Elkin BS, Gabler LF, Panzer MB, Siegmund GP. Clinical Biomechanics. 2019.
- Efficacy of Rugby Headgear in Attenuating Repetitive Linear Impact Forces. Knouse CL, Gould TE, Caswell SV, Deivert RG. Journal of Athletic Training. 2003.
- Why Most Traumatic Brain Injuries are Not Caused by Linear Acceleration but Skull Fractures are. Kleiven S. Frontiers in Bioengineering and Biotechnology. 2013.
- Mechanical disruption of the blood–brain barrier following experimental concussion. Johnson VE, Weber MT, Xiao R, et al. Acta Neuropathologica. 2018.
- The neurobiological effects of repetitive head impacts in collision sports. Hunter LE, Branch CA, Lipton ML. Neurobiology of Disease. 2019
- Leveraging Football Accelerometer Data to Quantify Associations Between Repetitive Head Impacts and Chronic Traumatic Encephalopathy in Males. Daneshvar DH, Nair ES, Baucom ZH, et al. Nature Communications. 2023.
- Predictors for Traumatic Brain Injuries Evaluated through Accident Reconstructions. Kleiven S. Stapp Car Crash Journal. 2007.
- What Is Brain Protection in Sport? Further Reading. Rezon.
- Why Do Women Face a Higher Risk of Brain Injury in Sport? Further Reading. Rezon.
- Wear and Care: How to Wear Rezon Halos®.
- Brain Protection Technology for Sport: Rotection®. Further Reading. Rezon.
- Our Laboratory Testing for Halos®.
- Independent Laboratory Testing for Rezon Halos®. Virginia Tech Helmet Lab.
- Brain Injury in Rugby: What Causes It and How to Reduce Risk. Further Reading. Rezon.
- Instrumented Mouthguards in Elite-Level Men’s and Women’s Rugby Union: The Incidence and Propensity of Head Acceleration Events in Matches. Tooby J, Woodward J, Tucker R, et al. Sports Medicine. 2024.
- Headgear Performance Specification. World Rugby. Regulation 12.
- Padded Headgear Does Not Reduce the Incidence of Match Concussions in Professional Men’s Rugby Union: A Case-Control Study of 417 Cases. Stokes KA, Cross M, Williams S, et al. International Journal of Sports Medicine. 2021.
- ‘Subconcussive’ is a dangerous misnomer: hits of greater magnitude than concussive impacts may not cause symptoms. Nowinski CJ, Rhim HC, McKee AC, et al. British Journal of Sports Medicine. 2024.
- Cumulative Head Impact Exposure Predicts Later-Life Depression, Apathy, Executive Dysfunction, and Cognitive Impairment in Former High School and College Football Players. Montenigro PH, Alosco ML, Martin BM, Daneshvar DH, et al. Journal of Neurotrauma. 2017.
- Injuries in recreational curling include head injuries and may be prevented by using proper footwear. Ting DK, Brison RJ. Health Promotion and Chronic Disease Prevention in Canada. 2015
- Epidemiology of Figure Skating Injuries: A Review of the Literature. Han JS, Geminiani ET, Micheli LJ. Sports Health. 2018
- Repetitive Subconcussive Head Impacts in Sports and Their Impact on Brain Anatomy and Function: A Systematic Review. Hack L, Singh B, Binkofski F, Helmich I. International Journal of Sports Medicine. 2024.
Author: Judith McMinn
