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2013 Risk factors for sports concussion: an evidence-based systematic review

Shameemah Abrahams, Sarah Mc Fie, Jon Patricios, et al.

Br J Sports Med published online September 19, 2013 doi: 10.1136/bjsports-2013-092734


Concussion is a common sports injury with approximately 1.6–3.8 million sport-related concussions reported in the USA annually. Identifying risk factors may help in preventing these injuries. This systematic review aims to identify such risk factors. Three electronic databases; ScienceDirect, PubMed and SpringerLink, were searched using the keywords ‘RISK FACTORS’ or ‘PREDISPOSITION’ in conjunction with ‘SPORT’ and ‘CONCUSSION’. Based on the inclusion and exclusion criteria, 13 628 identified titles were independently analysed by two of the authors to a final list of 86 articles. Only articles with a level of evidence of I, II and III were included according to robust study design and data analysis. The level of certainty for each risk factor was determined. A high level of certainty for increased risk of a subsequent concussion in athletes sustaining more than one previous concussion was reported in 10 of 13 studies. Further, a high level of certainty was assigned to match play with all 29 studies reporting an increased concussion risk during matches. All other risk factors were evaluated as having a low level of certainty. Although several risk factors were identified from the appraised studies, prospective cohort studies, larger sample sizes, consistent and robust measures of risk should be employed in future research. 

Sex - (Just one risk factor of many examined in this great study)

Twenty-three studies investigated whether there was a difference in concussion risk between male and female athletes (see online supplementary table S1.2). Four studies found men to be at increased risk,34–37 10 studies showed that women had a greater risk of concussion33 38–46 and nine studies found no association.47–55

Men were at a greater risk in youth alpine sports,35 youth American football,36 lacrosse34 and when comparing different sport types.37 However, comparing different sport types, between sexes, introduces a bias as men tend to play high- collision sports with increased concussion risk. Furthermore, men are often more willing to take more risks within the same sport.35 More studies are required to confidently assess sex dif- ferences in male-dominated sports, such as rugby and American football.

Women were found to have a 1.5-fold to 2.5-fold greater con- cussion risk in various levels of soccer.33 38–41 43–45 Two studies found no significant difference between male and female soccer players49 53 but included only 5 and 29 concussions, respect- ively, and therefore lacked statistical power. Women had a 1.5-fold and 3-fold higher concussion risk in the five studies on basketball populations.38 39 42 43 46 Four studies compared female softball and male baseball players with three studies reporting greater risk in softball players.38 40 41 43 Several pos- sible reasons for increased concussion susceptibility in women have been proposed. Female soccer players have been found to have increased head acceleration during impacts compared with males, indicative of decreased neck strength and effective head mass.56 57 It has been suggested that the increased head to ball ratio in female soccer players may also play a role.58 Another reason for higher concussion rates in women may be their increased willingness to report injuries.59

Nine studies observed no difference in concussion risk between sexes in taekwondo,47 50 51 soccer,49 53 collegiate rugby,48 lacrosse38 43 and when comparing different sport types.52 54 A possible confounding variable when comparing sex differences in lacrosse; is the difference in protective equipment and rules with physical contact reduced in the female game.

The results from these studies suggest that in sports where rules and physicality are more equal between sexes, such as soccer and basketball, women appear to be at greater risk. However, when all sports are collectively analysed, there is a low level of certainty that sex is a risk factor for concussion. Future studies should include measures of exposures so that a reliable correlation between sex and concussion risk may be established.

Additional info in systematic review table

This article cites 122 articles, 45 of which can be accessed for free at:  


This evidence-based systematic review provides descriptive ana- lysis of several risk factors for sports concussion. Specifically, athletes with a history of previous sport-related concussions were at a higher risk of sustaining another concussion which is supported by the findings of the new Zurich, 2012 consensus statement.2 In addition to previous concussion, match play increased concussion risk with high certainty and therefore a good estimate of risk may be established. All other risk factors have a low certainty that it associates with risk of concussion. Finally, the devastating effect on quality of life, especially in the athlete’s later years, of debilitating neurological complications such as CTE as a consequence of repetitive concussive head impacts are a concern. Consequently, more high-quality level I studies are needed to confirm factors which may modulate concussion risk to reduce concussion incidence, improve manage- ment of athletes at high risk and prevent serious health complications in the future.

2012: Concussions in Wheelchair Basketball

Complete abstract

Results: Within the sample of 263 wheelchair basketball players, 6.1% reported experiencing a concussion in the current season. Of those experiencing concussions during the current season, 44% did not report their concussion. Of those not reporting the incident, 67% did not because they did not want to be removed from physical activity. Analysis by sex indicated that 5.82% of the male athletes sustained a concussion during the current season, and 14.36% had sustained an injury during their athletic career. Female athletes, however, sustained concussions at a higher rate, with 6.67% having concussions during the current season and 30.6% during their athletic careers. Women were also 2.5 times more likely to sustain a concussion than men. Athletes were most likely to report their concussion to their coach (60% of concussed athletes).

Conclusions: The current investigation was consistent with previous research in that women were more likely to sustain a concussion than men, and injury rates were similar to those in able-bodied basketball. Further work is needed in concussion assessment in persons with disability, as well as greater education concerning concussion in disability sports.

2012: A prospective study of physician-observed concussion during a varsity university ice hockey season: incidence and neuropsychological changes

Complete abstract

Conclusions: Although the incidence of game-related concussions per 1000 athlete exposures in this study was half the highest rate reported in the authors' previous research, it was 3 times higher than the incidence reported by other authors within the literature concerning men's collegiate ice hockey and 5 times higher than the highest rate previously reported for woman's collegiate ice hockey. Interestingly, the present results suggest a substantively higher incidence of concussion among women (14.93) than men (7.50). The reproducible and significantly higher incidence of concussion among both men and woman ice hockey players, when compared with  -observed games, suggests a significant underestimation of sports concussion in the scientific literature.

2012: The Role of Age and Sex in Symptoms, Neurocognitive Performance, and Postural Stability in Athletes After Concussion

Complete abstract

Gender and Recovery PDF of  study

Results: Female athletes performed worse than male athletes on visual memory (mean, 65.1% and 70.1%, respectively; P = .049) and reported more symptoms (mean, 14.4 and 10.1, respectively) after concussion (P = .035). High school athletes performed worse than college athletes on verbal (mean, 78.8% and 82.7%, respectively; P = .001) and visual (mean, 65.8% and 69.4%, respectively; P = .01) memory. High school athletes were still impaired on verbal memory 7 days after concussion compared with collegiate athletes (P = .001). High school male athletes scored worse on the BESS than college male athletes (mean, 18.8 and 13.0, respectively; P = .001). College female athletes scored worse on the BESS than high school female athletes (mean, 21.1 and 16.9, respectively; P = .001).

Conclusion: The results of the current study supported age differences in memory and sex differences in memory and symptoms and an interaction between age and sex on postural stability after concussion that warrant consideration from clinicians and researchers when interpreting symptoms, specific components of NCT, and postural stability tests. Future research should develop and assess interventions tailored to age and sex differences and include younger (<14 years) participants.

2012: Video Incident Analysis of Head Injuries in High School Girls' Lacrosse

Girls Lacrosse PDF of Study

Results: Of the 25 head injuries (21 concussions and 4 contusions) recorded as game-related incidents by athletic trainers during the 2 seasons, 20 head injuries were captured on video, and 14 incidents had sufficient image quality for analysis. All 14 incidents of head injury (11 concussions, 3 contusions) involved varsity-level athletes. Most head injuries resulted from stick-to-head contact (n = 8), followed by body-to-head contact (n = 4). The most frequent player activities were defending a shot (n = 4) and competing for a loose ball (n = 4). Ten of the 14 head injuries occurred inside the 12-m arc and in front of the goal, and no penalty was called in 12 injury incidents. All injuries involved 2 players, and most resulted from unintentional actions. Turf versus grass did not appear to influence number of head injuries.

Conclusion: Comprehensive video analysis suggests that play near the goal at the varsity high school level is associated with head injuries. Absence of penalty calls on most of these plays suggests an area for exploration, such as the extent to which current rules are enforced and the effectiveness of existing rules for the prevention of head injury.

2012: American Medical Society for Sports Medicine Position Statement: Concussion in Sport

This is an excellent summary of concussions in sports but findings about women's concussions are not found until the section, Sex, on page six of the report.

  • Recent data suggest that in sports with similar rules female athletes sustain more concussions than their male counterparts.
  • In addition, female athletes experience or report a higher number and severity of symptoms as well as a longer duration of recovery than male athletes in several studies.

Studies by Manufactures of Products

(Pink lists studies by manufactures who study their products on women. We are not endorsing any particular product but rather just sharing information with the public on what studies have been done with female athletes.)

2010: Does gender influence cognitive outcome after traumatic brain injury? 

Gender & TBI PDF of study

Conclusions: The current study provided evidence that men and women receiving treatment for TBI do not differ significantly in cognitive outcome post-TBI, with the exception of visual memory, a finding that needs to be confirmed through replication. Questions that remain include how cognitive outcome post-TBI may be affected by the interaction between gender and other factors such as paediatric vs. adult injuries, hormonal changes, and existing structural differences in the brain between men and women. Future research on gender differences post-TBI is needed that includes measures of hormone levels, baseline functioning, and brain imaging, as well as samples that look at paediatric vs. adult injuries as moderating factors.

2009: Is there a gender difference in concussion incidence and outcomes?

Complete abstract

Conclusions: After evaluating multiple years of concussion data in comparable sports, the evidence indicates that female athletes may be at greater risk for concussion than their male counterparts. There also is some evidence that gender differences exist in outcomes of traumatic brain injury and concussions. Because concussion is a clinical diagnosis often depending on self reporting and with no established biological marker or consistent symptoms/definitions, and because there is evidence that females are more honest in reporting general injuries than males, it is unclear whether the concussion incidence data, while generally consistent in showing a higher risk in females as compared to males in similar sports, is a true difference or is influenced by a reporting bias.

2009:The Role of Concussion History and Gender in Recovery From Soccer-Related Concussion

Gender and Recovery PDF of study

Conclusion A history of concussion and gender may account for significant differences in postconcussive neurocognitive test scores in soccer players and may play a role in determining recovery. These differences do not appear to reflect differences in mass between genders and may be related to other gender-specific factors that deserve further study.


Our work with the Carleton U women’s hockey team is focusing on the magnitudes and frequency of head impacts. The 2012/13 study looked at just frequency ( whereas the 2013/14 study will add symptom reporting to the mix to see whether a team with sensors report/ assess more players with concussion symptoms compared to the control of teams without.

The 2012/13 Study

Shockbox helmet sensors were used on the Carleton University women’s ice-hockey team in 2012 to study head impacts in a supposedly non-contact league.

18 Players with an average age of 21 were fitted with Shockbox helmet sensors and monitored for half a playing season in all practices and games.

Shockbox helmet sensor (beta version) fitted to hockey helmets

Shockbox helmet sensor (beta version) fitted to hockey helmets

A researcher monitored the smartphone and video recorded all games/ practices to correlate all Shockbox alerts with actual head impacts on the ice.

Shockbox helmet sensors hockey study - Test setup

Shockbox helmet sensors hockey study – Test setup

Shockbox helmet sensors setup - University hockey study

Shockbox helmet sensors setup – University hockey study

In 18 games/ practices the Shockbox helmet sensors captured 68 video verified direct head impacts with an average of 97.7g ± 33.8g. Impacts were captured at 4 different locations with distribution percent at the front (11.7%), right (23.5%), left (19.1%) and rear (42.6%) locations.

Impacts by player - Shockbox CIS Hockey Study

Impacts by player – Shockbox CIS Hockey Study

Out of these impacts recorded, 4 players suffered concussions that were captured by the Shockbox helmet sensors and the athletic trainers were notified.

Concussions and impacts recorded by Shockbox helmet sensors

Concussions and impacts recorded by Shockbox helmet sensors

For each concussion that was diagnosed, the impact alert sensor was triggered and provided an average magnitude output of 105.3g±17.7g.

To view the full white paper – download here