Approximately 3.8 million concussions occur in the United States each year during athletic participation,1 with 1.1 to 1.9 million occurring in patients younger than 18 years.2 Impacts to the head have been confirmed as the leading cause of concussion in sport3 and have been linked to neurocognitive changes both immediately and later in life in soccer participants.3–16 Understanding concussion symptoms and educating individuals regarding the treatment and prevention of concussion are key elements to limiting its effects on society.17
Helmet- and head-mounted monitoring devices have increased our understanding of the profile of head impacts that may cause concussions. In addition to research on head impact biomechanics, sensors are being used to aid concussion diagnosis.18 Some authors have suggested that concussions are only sustained after a specific magnitude or duration of an impact.19 However, the studies in that meta-analysis only analyzed head impact data from male participants, and no studies were able to determine the exact characteristics of the rotational and/or linear accelerations needed to cause concussion.17,18,20 Therefore, there is currently no specific threshold that can be used to aid concussion diagnosis.
Although a growing body of literature has investigated head impacts in soccer athletes, we have not seen biomechanics of concussions reported in the literature for women's soccer or women's lacrosse participants. Wilcox et al.21 found much lower impact magnitudes for women's hockey players who sustained concussions compared to men. If clinicians have a greater understanding of the mechanism of concussions, more focused preventative initiatives could be undertaken to help reduce their occurrence and identification may be ameliorated. Therefore, the purpose of this preliminary case series was to present the head impact biomechanics of concussive impacts in women's lacrosse and soccer athletes.
The participants, who were also part of a larger study, were four National Collegiate Athletic Association (NCAA) Division III women's lacrosse (n = 2) and soccer (n = 2) athletes (age = 19.20 ± 1.10 years; height = 64.00 ± 1.58 cm; weight = 59.09 ± 2.55 kg). The larger study examined head impact biomechanics in women's soccer and lacrosse athletes. During 2 years of data collection for the larger study, there were a total of four diagnosed concussions: two in soccer and two in lacrosse.
Instrumentation and Operational Definitions
The X2 Biosystems xPatch sensor (X2 Biosystems, Inc., Seattle, WA) was used to collect data. Head-mounted systems have been found to be more accurate in determining linear and rotational accelerations than helmet-mounted systems,22 and skin patches had a lower variance in linear acceleration when compared to helmet-mounted sensors, mouth guards,23 and other head-mounted sensors.24 However, the xPatch has also been shown to overestimate25 and underestimate22 linear and rotational accelerations, potentially due to skin movement.25 One study also found that the xPatch tended to underpredict impacts.24 The sensors recorded the frequency, magnitude, duration, and location of head impacts that were sustained during practices and games.
This study was approved by the institutional review board of the host institution prior to data collection and all participants signed an informed consent form before participation. Before every practice and game, we applied a protective spray (Cavilon; 3M, St. Paul, MN) to reduce skin irritation before affixing the sensor over the right mastoid process. A member of the research team filmed every practice and game during the season from a point high above the field using a broad view during practices and following the flow of play during games. At the end of the season, we compiled the data into Microsoft Excel (Excel 2016; Microsoft Corporation, Redmond, WA) for analysis.
During the season, participants were asked to report to their athletic trainer if they experienced any concussive symptoms. All concussions were confirmed by an athletic trainer and a physician based on the definition provided by the Consensus Statement on Concussion in Sport26 and physical examination findings. We gathered information on the concussive event from the participants and reviewed the impact data and film from the day of injury to confirm the concussive event and specific head impact.
A total of four concussions were confirmed on video and included in this study. Biomechanical descriptions of the impacts that caused the concussions are listed in Table 1.
Biomechanical Data of Concussive Impacts
The purpose of this study was to present the head impact biomechanics of women's lacrosse and soccer athletes with concussion. Similar to women's hockey players (average concussive impact biomechanics = 43.0 ± 11.5 g; 4,030 ± 1,435 rad/s2),21 our participants suffered concussions with much lower peak linear accelerations (average concussive impact biomechanics = 24.38 ± 29.42 g; 6,427.52 ± 3,932.55 rad/s2) than those for football players across nine studies (pooled mean concussive impact biomechanics = 98.68 g; 95% confidence interval [CI] = 82.36 to 115.00; 5,776.60 rads/s2; 95% CI = 4,583.53 to 6,969.67).19 However, sustaining an impact of greater than 90 g failed to produce neurocognitive or balance deficits in college football players27 supporting a lack of an injury threshold. Similar to findings with women's hockey players,21 our results indicate that only one concussive impact was within the ranges reported in a meta-analysis.19 Other studies reported an increased frequency of head impacts and impacts with more severe kinematics on the day of diagnosed concussion.28 However, it is unknown whether many small impacts or fewer larger impacts are more likely to cause injury. Our participants experienced relatively few impacts on the day of diagnosed concussion and relatively low peak cumulative linear and peak rotational accelerations on days of diagnosed concussion compared to those reported previously.28
An exact threshold has not been identified for concussion, potentially because only peak linear and peak rotational accelerations are typically used. It has not been confirmed that these measures are appropriate for concussion risk, and the relationship between these measures and brain injury remains unknown.18 Determining an injury threshold could aid the recognition of concussive head impacts, but factors such as impact duration,29 density,30 or kinematic impulse31 may need to be taken into account.
Another consideration with the thresholds that have been proposed is that they are all based on concussive head impacts in men. Tierney et al.32 found that acceleration forces while heading soccer balls were greater in women than in men. Because ball speed was consistent between the sexes, these results suggest that men and women react differently to similar impacts. Additionally, women have been found to be more forthcoming with concussive symptoms,33 which could also explain the differences between biomechanics of diagnosed concussions. Because the established thresholds are based on data from men, our results and those of others21 suggest the thresholds are not appropriate for women, perhaps due to the typical physiological differences between the sexes.
Limitations and Future Research
Our study has limitations. There was a limited number of reported and diagnosed concussions. Our study may not generalize to a broad population of female athletes. Another limitation and caveat is the difference in sport mechanics that are included in this case series. We included women's soccer and lacrosse, but the results were compared to football and ice hockey. Future studies will need to be completed to either confirm or refute the current findings. Future research should examine concussive impacts that include a wider variety of male and female sports with a larger sample size. It would be interesting to discover if athletes suffer concussions at different magnitudes based on sex, sport, and/or competitive level. Another limitation was using the xPatch for data collection. Although the xPatch is an accurate tool, there was likely some degree of measurement error. Future studies should include different measurement tools and laboratory reconstructions of concussive head impacts in female athletes.
Implications for Clinical Practice
Based on our results, we suggest injury thresholds may not be generalizable for all populations, and we caution against using impact biomechanics for concussion diagnosis. Perhaps factors outside of impact biomechanics need to be considered in concussion diagnosis such as sex, prior concussion history, comorbidities such as learning disabilities and mental illness, neck strength, and player awareness, among other factors.
All of the concussions in the current study were caused by impacts to the side or front of the head. This finding is similar to concussion reconstructions in professional football, where the mechanism was impact to the side or front of the helmet.34 Collegiate football players with concussion suffered more impacts to the side and top of the helmet on the day of injury.35 Impacts to the front of the head were most likely the cause of concussions in collegiate and high school football players.36 Side impacts were also the most common cause of concussions in scholastic lacrosse players.37,38 Therefore, impacts to the side and front of the head are concerning across multiple sports, and these impacts should be focused on when implementing preventative measures to reduce the frequency and severity of head impacts.
Both observed mechanisms were illegal for women's lacrosse players (stick-to-head) but legal for women's soccer players (head-to-head or head-to-ground). An additional emphasis on calling penalties for stick-to-head contact during women's lacrosse participation in both games and practices may be warranted. It is important to note that the one concussive impact we recorded in a women's lacrosse game was penalized. Perhaps stiffer penalties may deter illegal contact to the head and should be considered.
Our results indicate the average head impact biomechanical data that caused concussions in women's lacrosse and soccer participants is much lower than those reported for men. These results suggest concussions are heterogeneous from a mechanism standpoint, especially across sex. The variability within our results indicates that the use of helmet- and/or head-mounted sensors for concussion diagnosis should be cautioned against.
- Langlois JA, Rutland-Brown W, Wald MM. The epidemiology and impact of traumatic brain injury: a brief overview. J Head Trauma Rehabil. 2006;21:375–378. doi:10.1097/00001199-200609000-00001 [CrossRef]
- Bryan MA, Rowhani-Rahbar A, Comstock RD, Rivara FSeattle Sports Concussion Research Collaborative. Sports- and recreation-related concussions in US youth. Pediatrics. 2016;138:e20154635. doi:10.1542/peds.2015-4635 [CrossRef]
- Crisco JJ, Wilcox BJ, Beckwith JG, et al. Head impact exposure in collegiate football players. J Biomech. 2011;44:2673–2678. doi:10.1016/j.jbiomech.2011.08.003 [CrossRef]
- Lipton ML, Kim N, Zimmerman ME, et al. Soccer heading is associated with white matter microstructural and cognitive abnormalities. Radiology. 2013;268:850–857. doi:10.1148/radiol.13130545 [CrossRef]
- Witol AD, Webbe FM. Soccer heading frequency predicts neuro-psychological deficits. Arch Clin Neuropsychol. 2003;18:397–417. doi:10.1093/arclin/18.4.397 [CrossRef]
- Zhang MR, Red SD, Lin AH, Patel SS, Sereno AB. Evidence of cognitive dysfunction after soccer playing with ball heading using a novel tablet-based approach. PLoS One. 2013;8:e57364. doi:10.1371/journal.pone.0057364 [CrossRef]
- Koerte IK, Ertl-Wagner B, Reiser M, Zafonte R, Shenton ME. White matter integrity in the brains of professional soccer players without a symptomatic concussion. JAMA. 2012;308:1859–1861. doi:10.1001/jama.2012.13735 [CrossRef]
- Koerte IK, Lin AP, Muehlmann M, et al. Altered neurochemistry in former professional soccer players without a history of concussion. J Neurotrauma. 2015;32:1287–1293. doi:10.1089/neu.2014.3715 [CrossRef]
- Koerte IK, Mayinger M, Muehlmann M, et al. Cortical thinning in former professional soccer players. Brain Imaging Behav. 2016;10:792–798. doi:10.1007/s11682-015-9442-0 [CrossRef]
- Matser EJ, Kessels AG, Lezak MD, Jordan BD, Troost J. Neuropsychological impairment in amateur soccer players. JAMA. 1999;282:971–973. doi:10.1001/jama.282.10.971 [CrossRef]
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- Bazarian JJ, Zhu T, Zhong J, et al. Persistent, long-term cerebral white matter changes after sports-related repetitive head impacts. PLoS One. 2014;9:e94734. doi:10.1371/journal.pone.0094734 [CrossRef]
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- Tyson AM, Duma SM, Rowson S. Laboratory evaluation of low-cost wearable sensors for measuring head impacts in sports. J Appl Biomech. 2018;34:320–326. doi:10.1123/jab.2017-0256 [CrossRef]
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- McCrory P, Meeuwisse W, Dvořák J, et al. Consensus statement on concussion in sport-the 5th international conference on concussion in sport held in Berlin, October 2016. Br J Sports Med. 2017;51:838–847.
- McCaffrey MA, Mihalik JP, Crowell DH, Shields EW, Guskiewicz KM. Measurement of head impacts in collegiate football players: clinical measures of concussion after high- and low-magnitude impacts. Neurosurgery. 2007;61:1236–1243. doi:10.1227/01.neu.0000306102.91506.8b [CrossRef]
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- Tierney RT, Higgins M, Caswell SV, et al. Sex differences in head acceleration during heading while wearing soccer headgear. J Athl Train. 2008;43:578–584. doi:10.4085/1062-6050-43.6.578 [CrossRef]
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Biomechanical Data of Concussive Impacts
|Peak LA (g)
|Peak RA (rad/s2)
|Cumulative LA (g)b
|Cumulative RA (rad/s2)c
|Mechanism of impact
||Game (legal impact)
||Game (penalized illegal impact)