Is the risk of concussion higher amongst female athletes?

Female sport is on the up. Record levels of participation at grassroots have been inspired by growing professionalism and elite performance amongst the very best. FIFA has described women’s football as the ‘single biggest growth opportunity in football’. World Rugby states that a quarter of the playing population is now female with a 28% increase in registered players since 2017. A similar story exists in Australia where latest figures show that 40% of grassroots Aussie rules players are female, up from 30% in 2017 when the AFLW launched.

At the summer Olympics the growth in female representation also continues its upward trajectory. Of the nearly 11,000 athletes that took part in the Tokyo Games nearly 49% were women, up from 45.6% in Rio and 44.2% in London 2012. While these increases are to be celebrated, the focus on growth has, particularly in sports with male equivalents such as football, rugby and hockey, uncovered an increased risk of concussion amongst female athletes.

Concussion in female athletes

Perhaps due to the difference in male and female sporting participation, for years the relative level of female concussion in sport didn’t seem a cause for concern. Now, with an increased knowledge of the seriousness of the condition and the growth in female sport the issue is beginning to gain recognition.

Evidence is now emerging of the relative higher risks female athletes face. Indeed, in some cases being female is listed as an enhanced risk factor. In comparable sports, female participants have been shown to have up to twice the risk of experiencing concussion as men. A study published in 2017 tracking concussion in American high school sport showed that female soccer had surpassed American football as the sport with the highest rates of concussion (Schallmo et al 2017).

Differences in symptoms, symptom severity and duration of symptoms are also now being reported in comparison to male counterparts. This means that female athletes are likely to suffer more time on the sidelines due to concussion. Many female athletes are not fully professional, or use university programmes to progress their sporting careers. Therefore, If symptoms are prolonged, it can have wider ramifications in terms of employment and academic study.

This became a reality for AFLW player Kirsten McLeod. During pre-season training ahead of the 2022 season, McLeod suffered a number of blows to the head. The injuries led to a difficult decision to take a year out of the game to focus on recovery. However, her concussions have affected her ability to work. In an ABC news article she explained some of the issues she is now facing in a work environment. "I've noticed things like I can't concentrate for as long; I muddle up my words. And I always have to have a pen and paper with me to just make sure I get everything down because otherwise, I'll just forget”.

Why the difference?

The big question for researchers is why does concussion in female athletes present itself differently to males. A number of reasons have been offered. However, due to the lack of female specific research examining sport related concussion the available evidence upon which to base any definitive answers remains limited. Despite this, four main areas have been highlighted as possible reasons, either independently or as a combination.

Neck strength
In research examining concussion in female soccer, particularly coming from high school and college systems in America, neck strength has been an area of focus. Soccer is one of the few, if not the only sport where the head is commonly used to control, pass and strike the ball. As such, recent research examining links to heading and concussion as well as heading and other neurodegenerative conditions has begun to gain significant media attention.

Female players are more likely to suffer a concussion from head to ball contact when compared to their male counterparts. In the male game, most concussions occur via player to player contact. One reason often cited for the increased risk of concussion linked to heading the ball is reduced neck strength amongst female players. Studies specifically looking at soccer players have found female players have significantly less strength. A much referenced study from 2008, actually showed that female players had 50% less isometric neck strength compared to male players. Reduced neck strength presents a problem as it may render players unable to absorb or stabilise their heads effectively whilst heading the ball. This leads to increased head acceleration with the potential for increased brain movement inside the skull. It is this mechanism that may underpin the heightened concussion risk factor amongst female players.

To combat a lack of neck strength, additional training has been proposed. Whilst research has been able to show that increasing neck strength does lead to reduced head acceleration, only one paper has been able to then link this to a reduced risk of concussion. Again using high school athletes as test subjects Collins et al (2014) described a 5% decrease in concussion risk per pound of increased neck strength.

Head acceleration
Head acceleration as an issue in female concussion is, in many ways, linked to neck strength. If female athletes don't have the neck strength to limit head acceleration then they are more likely to suffer concussion caused by lower level impacts. This would mean that if the exact same impact force was applied, male head acceleration would be significantly less than female head acceleration therefore the risk of female concussion is higher.

However, some evidence exists that highlights the issue being more complicated than just neck strength differences. A case study in 2019 by Sayre et al, showed that two college level female athletes had suffered concussion at significantly lower head acceleration levels than that observed in male athletes. While no definitive threshold has been established for head acceleration forces that will result in concussion, the potential for a lower threshold amongst women is an area that will need further evaluation.

Hormonal
One of the most intriguing areas of investigation when looking at female concussion is the potential role of sex hormones and the menstrual cycle. A report in 2019 highlighted a possible window within which the risk of concussion may be increased. The study showed that 66.7% of concussion occurred within nine days coinciding with the late luteal phase and first two days of menstruation. Zooming in a little more, just the late luteal phase accounted for 50% of concussions (La Fountaine et al 2019).

This is an area that needs major focus and significantly more study in order to draw any solid concussions. However, the rise in concussion incidence would fit with a drop in both progesterone and oestrogen. These hormones have a neuroprotective effect which includes the promotion of myelin formation, protection of neurons and the optimisation of cell survival.

Brain structure
Internal factors such as hormone levels and brain structure and function have received much less attention than the external factors of neck strength and head acceleration. Nonetheless, the limited research that has taken place does show the need for further investigation. Currently brain structure and function analysis points more towards longer term neurodegenerative issues rather than instant concussive incidence (Rubin et al 2018).

In research examining the impact of heading on brain microstructures, results showed that when exposed to similar head impacts women exhibited greater changes in white matter compared to men. White matter plays a major role in communication within and between the brain and spinal cord. Often changes are associated with reductions in sensory, motor and cognitive function. The authors highlight that sex based differences in suseptibility to brain injury need further investigation to understand why it is happening and the best course of action in terms of interventions (Rubin et al 2018).

What is the difference?

In addition to suffering from a higher incidence of concussion, evidence exists to suggest that female athletes also suffer from a greater number of symptoms, more severe symptoms and also a longer duration of symptoms. In 2005, a study from the USA was among the first to highlight female concussion symptom disparities. It reported that female athletes had a wider range of symptoms and greater drops in cognitive performance. Evidence continues to support this notion but caution has also been expressed before drawing absolute conclusions. This is because women suffer more frequently with symptoms such as migraines unrelated to concussion or head impacts. This leads to the suspicion that reports can overestimate the severity and duration of symptoms directly attributable to concussion.

The reliance on patients to self report symptoms to manage recovery has also been discussed as a possible explanation for gender differences. As with much of the research conducted within the female concussion space, evidence from high school athletes has shown that females are more open about reporting symptoms. This could account for differences seen in symptom duration.

Of course, neither of these two considerations remove the incidence of concussion in and of itself. Furthermore, a recent review study examining results from 25 papers continued to point to an increased burden amongst female athletes (McGroarty et al 2020). One such athlete to understand the severity of concussion is former Northern Ireland and Crystal Palace football (soccer) player, Freya Holdaway. Freya was forced to retire from football in 2020 after suffering from 3 concussions in the space of 18 months. The first she describes as the “classic egg but it wasn't too sore”. The second however she classed as “a bit more sinister”.

After coming off, she passed the initial pitch side tests, but while walking back to the bench she began to feel unwell. She passed out and suffered two pitchside seizures. Freya missed the remainder of the season and the following pre season so she could focus on her recovery - a period of roughly 4 months. Once back playing with Crystal Palace in the FA Women’s Championship, another concussion forced her to question her future. Palace is not fully professional so Freya had to work as well as maintain a high level sporting career. Weeks after the third concussion she continued to struggle. “My ears were ringing and I ended up taking a month off work because looking at a laptop for eight hours a day was giving me excruciating headaches. It got to the point where I was sleeping for 12 hours, that's just not like me but at the same time I clearly needed it."

As the Covid Pandemic forced the UK into lockdown, the time out of the game enabled Freya to take an extended break from the game. "That break from not heading a ball in training or games, it's difficult to explain, but I started feeling so much better.

"I felt more settled and my head was in a good place. It was the best I felt in two years. In hindsight I wasn't really ok before that, but at that point in time not being ok became my normal”.

A four year study assessing the differing consequences of concussion between males and females has recently been published. It had 986 subjects (45% female) who presented to a concussion clinic in the USA. The vast majority of cases were sport related (83% females, 90% males). The results showed that females not only suffered a greater range of concussion symptoms, but that the symptoms were also more severe. In fact, of the 22 listed symptoms, females reported 21 of them and of these, suffered greater severity 91% of the time (20 out of the 22 symptoms). The difference in severity was also stark: Female severity scores (via the Global Severity Index) were 77% higher than those seen in males.

It is also interesting to note that more males suffered from a loss of consciousness (17% versus 9% in females). Male evaluations took place 6 days following the injury whilst female evaluations were at 9 days post injury (median values). Yet despite a longer recovery period between injury and evaluation and a lower proportion of one of the most dramatic symptoms, this study still saw greater symptom prevalence and severity amongst female subjects. The authors highlight that these differences in symptom distress levels may influence variations in recovery and therefore the need to examine sex specific management of post concussion treatments.

The research gap

Despite general increases in knowledge regarding concussion, much of the research remains male focused. Comparison studies are available, but many pull data from high school and college aged females. This means most of the subjects are still going through developmental stages prior to full maturation and adulthood. Therefore drawing conclusions about the causes, diagnoses and treatments to apply to elite adult female athletes could be problematic.

Whilst it is widely accepted that more research is needed into female concussion, consensus does exist that the incidence of concussion amongst female athletes is higher than in their male counterparts. However, the answer to the key question of ‘why?’ remains unanswered. It is fundamentally important that this question is given significant focus, as, until we know why female concussion is more prevalent, credible strategies to mitigate prolonged injury will remain elusive.

The rules of the game

Concussion isn’t limited to sports that males and females play with the same rules, but as has been mentioned within this article, the instances of concussion in those sports are significantly higher in females. Rule changes have been passed across sports at junior levels to protect younger players from the effects of head impacts. As female sporting participation grows, the authorities may want to consider adapting rules to help protect female players.

Rules are constantly being updated to protect player safety. International governing bodies such as World Rugby have examined tackle rules with the aim of reducing direct blows to the head. Soccer has moved to allow concussion substitutes and in 2020 the AFL made an almost immediate change to protect players' heads following the Shaun Burgoyne sling tackle on Geelong’s Patrick Dangerfield. However, at present it doesn’t seem to have had much impact in terms of helping to protect females and improving the statistics related to the over indexing of female concussion.

An area that does need immediate attention is concussion protocols. Although these are continuously under review by national and international governing bodies’ medical panels, increasing evidence points to the need for sex based guidelines. This will hopefully ensure individuals are given the support they need, particularly in terms of prolonged symptom duration amongst female athletes. In many instances, the standard 14 day break from the sport might not suffice. By increasing the recovery window for female players, it could reduce the pressure to return to play, allowing for enhanced recovery.

HITIQ and female concussion

As has been mentioned throughout this article, more female specific concussion research is needed. Greater clarity into the subject will help authorities develop rules to mitigate the risk of concussion amongst female athletes and support better recovery strategies. HITIQ is already working with the AFLW and Scottish Rugby to ensure their players benefit from the most advanced impact detection system on the market. The aim is to help medical teams supporting these players manage and mitigate concussive impacts allowing them to spend more time on the field, injury free.

HITIQ is serious about supporting women’s sport. It is currently looking to partner with teams and research projects to help bring more understanding to the topic. If you are interested in a collaboration with HITIQ, its expertise and next generation concussion management technology, get in touch via the contact form on the website.

Conclusion

Evidence shows that the risk of concussion is higher amongst female athletes compared to men playing the same sport. Whilst reasons for this are still not clear, researchers have offered a number of suggestions including lower neck strength, different head acceleration tolerances, the results of hormonal cycles in females and even differences in brain structure alterations following impacts. It has also been observed that females suffer an increased number of concussion induced symptoms, greater symptom severity and prolonged symptom duration.

In order to protect female players across sport more research is needed to understand the mechanics and mechanisms underpinning these sex based differences in concussion consequences. However, we are keen to do more. So, if you have a project you think would benefit from support via HITIQ’s expertise and technology please get in touch via the contact form on the website.