Documentation:FIB book/Taekwondo Head Impact

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Introduction

Taekwondo Competition

Taekwondo is a famous Korean martial art. This full contact sport allows kicks to the head but not punches. The use of protective equipment including headgear, torso protection, and a mouthguard during taekwondo sparring is necessary. High-impact kicks such as roundhouse kicks or spinning kicks can result in rapid brain acceleration or deceleration, leading to brain concussions.[1] Head injuries in taekwondo have obtained significant concern due to the severity of trauma. In the long term, it may cause mild cognitive impairment for retired athletes.[1] The concussion rate in taekwondo is reportedly 3.1 times higher than in college football games.[2] In a world class taekwondo competition, eight competitors experienced concussions, accounting for a rate of 7.86 per 1,000 athlete-exposures.[3]

In the early 2000’s there were demands from the International Olympic Committee for the World Taekwondo Federation (WTF) to provide transparency in the scoring process because of alleged fixed matches.[4] This incident triggered various rule changes by the WTF over the past decades which have put more emphasis on employing head strikes, increasing the risk of head injury.[4] Such rule changes include increasing the points for head contact from 1 to 2 points in 2003.[4] Again in 2009 the WTF amended this rule to assign 3 points for a kick to the head.[4] By 2010, an additional one point was awarded if a turning kick was used to execute the head strike.[4] Now as of 2023, a turning kick to the head earns 5 points.[5] This gradual increase in points for head attacks has led to a greater incentive for competitors to employ head strikes, thereby increasing the risks of head injury. In particular, a turning kick which now earns 5 points, has greater angular momentum, resulting in larger magnitude of force and greater risk of brain damage.[6] These rule changes were motivated by the need to enhance the entertainment value of taekwondo matches with little regard to athlete impact.

With the use of headgear and a mouthguard, the risks of concussion decreases by around 50% in other contact sports.[7] However, despite taekwondo athletes wearing the aforementioned protective equipment there is no evidence that this equipment reduces concussions at all.[6] [8] It has even been suggested that the thickness of headgear could potentially increase the rotational acceleration of the head thus, increasing the risk of brain damage.[6] Furthermore, in June 2023 the Association of Ringside Physicians released a statement that head guards should not be relied upon to reduce the risk of concussion or brain injury but only to reduce the incidence of facial lacerations.[8]

It is important to evaluate the forces that occur during taekwondo sparring and competitions to understand how headgear can be used to reduce the risk of head injury. In this article, the first section covers the analysis of head impact, athlete safety, data collection techniques, biomechanical head impact measurements in taekwondo, and the effectiveness of protective headgear, summarized from the literature review. The second section discusses the problems and controversies in existing research methodologies. Lastly, the concluding section addresses future work in this field.

Previous Work

Impacts to the Head

In a full contact sport such as taekwondo where points are awarded for blows to the head and knockouts, head impacts are not only inevitable, they are often encouraged. There are two primary factors to evaluate with respect to head impacts: the frequency of impacts and the force of each individual impact. At this point the literature is uncertain whether repeated sub-concussive impacts will result in long term injury; however, small changes in white matter have been noted following repeated impacts which suggests that it is important to reduce the frequency of these impacts.[9] The forces experienced by the head have a clear relationship with injury which will be explored further on in this section.

A better understanding of the frequency of head impacts and the force of each impact may allow for engineered solutions to keep athletes as safe as possible while competing. Possible engineered solutions include protective headgear, which will be discussed at the end of this section as a tool to reduce athlete injuries.

Factors Affecting the Likelihood of Head Impacts

There are multiple factors which will influence the incidence of head impacts including age, sex, body proportions, and more.

Age was identified as an influencing factor as middle school students were identified as being more likely to receive head blows than older competitors.[10] Additionally, athletes who used blocking skills were less likely to receive head blows which may be related to age and experience in the sport, although blocking is not a commonly used skill based on these analyses.[10][11]

Sex may influence head blow incidence, though it is unclear as one study identified that high school males and middle school females had higher incidence rates; however, other studies have identified that female athletes received more head kicks, likely because female athletes tend to favor head kicks compared to male competitors.[10][11][12]

Body composition may influence the likelihood of head impacts. The frequency of head impacts tends to be higher in the lightweight categories for both males and females suggesting that lower competition weight may be proportional to risk of head blows.[11] It appears as though having competing athletes who are of similar height may have a slight increase on the frequency of head kicks; however, there is no increase in frequency if there is a significant height difference between the two athletes.[11]

Injury history may also influence head blows as competitors with a history of receiving a blow to the head were less likely to receive one during this competition.[10] Interestingly, a trend showed that the colour of head and torso protector may affect the likelihood of head impacts such that athletes who wore red protectors experienced more head blows than athletes wearing blue protectors.[11]

Frequency of Head Impacts

One study looked at the frequency of head impacts during a large tournament with 2,328 school-aged athletes ranging from 11 to 19 years old.[10] This study identified 1,009 significant blows to the head based on video recording of the tournament across 736 competitors, which averages to 1.37 blows per competitor.[10] The same group conducted a similar study with competition observations in 2011 and 2013, and found that there was a significant increase in kicks to the head, which they hypothesized was related to a rule change in 2009 which increases the competition point value for head kicks.[11] The incidence of head kicks was 2.1 times higher in 2013 than in 2011, which presumably increased from 2004 due to the rule change.[11] A 2022 study noted an average of more than 2 kicks to the head per match (2.8 for females, 2.1 for males).[12] This increase in incidence of blows to the head makes it more important than ever to evaluate the likelihood of head strikes and the forces experienced during each strike to ensure that athletes are being protected as much as possible.

Data Collection

In order to understand head injury mechanisms in taekwondo, biomechanical parameters must be characterized. Linear and rotational acceleration are the most important kinematic parameters measured in taekwondo research as they allow researchers to quantify the risk of brain injury and make recommendations to enhance safety in the sport. The following section will summarize the different types of data collection prominent in the research surrounding taekwondo impact biomechanics.

Wireless Monitoring

One method of data collection involves instrumenting participants heads with wireless sensors and measuring the linear and rotational accelerations during their normal training and sparring sessions.[13] There is an abundance of sport studies that use wireless sensors to monitor head impacts in hockey, football and rugby although, to date this is the only study for taekwondo. Each participant wore a wireless wearable impact sensor called the X Patch placed behind their ear.[13] Linear acceleration, rotational acceleration, rotational velocity, and impact location were determined by the X Patch and head injury criterion (HIC) was calculated from the linear acceleration.[13] The impact location determined from the X Patch may also be useful in designing protective headgear.

Computer Simulations

A newer method in impact biomechanics studies is the use of computer simulations. These simulations can be used to estimate linear and rotational head acceleration resulting from a taekwondo kick to the head. One such study analyzed the linear and rotational head accelerations of a roundhouse kick using Automated Dynamic Analysis of Mechanical Systems (ADAMS) software.[14] This study chose the roundhouse kick as it is most commonly associated with mild traumatic brain injury in taekwondo competitions.[14] In the simulation a clamped free beam model was used to simulate head and neck movements while foot characteristics were obtained from 50th percentile male anthropometric data.[14] Once the mechanical properties were determined the system motion constraints were created using leg rotation about the thigh axis with a rotational spring.[14] Benefits of computer simulations include increased repeatability of the tests and fewer resource expenses.

Hybrid II and Hybrid III Studies

Lastly, another method to collect data is through the use of a Hybrid II or Hybrid III crash test dummy fitted with a protective helmet and instrumented to measure linear and rotational acceleration, head velocity and head injury criterion.

One such study aimed to evaluate the impact of Olympic level taekwondo kicks on resultant head linear acceleration (RLA), HIC and head velocity (HVEL).[15] To facilitate this, the head and neck of a Hybrid II 50th percentile crash test dummy was used as a kicking target for 12 male athletes with experience competing at a minimum A-class international level across various weight categories.[15] The test dummy head and neck was secured to a height adjustable frame to accommodate the weight categories of the athletes and permitted flexion/extension, right/left lateral flexion, and left/right rotation when the head was impacted.[15] Lastly, the test dummy was fitted with a head guard and instrumented with a triaxial accelerometer.[15] Following familiarization with the dummy, each athlete performed five repetitions of five different kicks (turning kick, clench axe kick, front leg axe kick, jump back kick, jump spinning hook kick).[15] Resultant linear acceleration was measured using the triaxial accelerometer and HIC was calculated based on the measured acceleration.[15]

Another group performed a similar study with the same setup, instead using a Hybrid III 50th percentile crash test dummy and three orthogonal angular rate sensors to allow measurement of rotational acceleration in addition to linear acceleration.[16] Another difference in this study was the evaluation of two ITF style kicks (turning kick and spinning hook kick) performed by non-elite level participants.[16] In taekwondo there are two competition styles: WTF and ITF. With ITF typically being light contact and WTF which is competed in the Olympics, being full contact with knockouts considered legal.[16] The previous study evaluated WTF style kicks in elite athletes while this study evaluated ITF style kicks in non-elite athletes. As there are approximately 80 million non-elite taekwondo athletes worldwide, it is imperative to assess the accelerations experienced in both the elite and non-elite populations to compare potential variations in the risk of head injury.[16]

Forces Experienced From Head Impacts and Injury Thresholds

Though the frequency of blows to the head is an important factor in determining athlete risk of head injuries, it is also critical to identify and understand the forces that the head and surrounding structures will experience during and after a strike to the head.

Two of the most commonly studied variables across the literature are linear and rotational acceleration. Any strike to the head will create both linear and rotational acceleration, a concept which is vital to predicting the severity of head injury.[17] The majority of blows to the head appear to be of low magnitude for both linear and rotational acceleration; however, it is important to characterize these magnitudes to ensure that athletes are not at excessive risk of head injury.[13]

Linear Acceleration

There are a variety of forces and factors which may lead to head injuries such as concussions; however, it has been suggested that evaluating linear acceleration alone may hold similar utility as a predictor of concussion.[13] Linear accelerations occurring from head blows in a high school taekwondo sparring session ranged anywhere from 10 to over 70g, with the majority (87.1%) falling between 10 and 30g.[13]

One group observed linear accelerations using the mounted ATD head method described above which ranged from 34.49 ± 17.89g to 130.11 ± 51.67g, depending on the type of kick used.[18] Another study determined that the linear accelerations ranged from 39 to 102g depending on the kick.[17] A final study with a similar method of a mounted dummy head observed a mean linear acceleration of 69.6 ± 37.9g and 70.8 ± 38.9g for hook kicks and turning kicks respectively.[16] Though these studies all noted different ranges of linear accelerations, they are all significantly higher than the forces observed in the live sparring sessions described above. This suggests that forces are higher in a more controlled environment as athletes are able to aim better and can generate as much force as possible when they are not concerned about blocking for their own safety.

It has been suggested that the tolerable reversible brain injury level is less than 85g of linear acceleration.[19] Based on this, it appears as though the majority of impacts measured during live sparring sessions would be considered sub concussive; however, almost 13% of blows would be concussive and this threshold does not account for the accumulative effect that repeated blows to the head would have on the brain.[13][9]

Table 1: Comparing measured linear accelerations from various taekwondo studies
Paper Strike Linear Acceleration (g) ATD Headform Used
O'Sullivan and Fife, 2017[13] Live sparring sessions 24 ± 22 Live sparring - no ATD
Fife et al., 2018[16] Hook kick 69.6 ± 37.9 Hybrid III
Turning kick 70.8 ± 38.9
O'Sullivan et al., 2016[17] Turning kick (university) 95 ± 46 Hybrid II
Spinning back (university) 64 ± 41
Spinning hook (university) 66 ± 34
Fife et al., 2013[18] Roundhouse 130.11 ± 51.67 Hybrid II
Front axe 34.49 ± 17.89
Clench axe 54.95 ± 20.08
Jump spinning hook 98.90 ± 27.11
Jump spinning back 83.82 ± 57.14

Rotational Acceleration

In addition to linear acceleration, rotational acceleration must also be assessed to fully understand the forces occurring at the head.[16]

Head rotational acceleration during high school sparring matches ranged from under 4,600 radians per second squared (rad/sec2) to greater than 7,900 rad/sec2 with an average of 4,726 ± 1,931 rad/sec2 per impact.[13] Of these recorded impacts, 17.1% and 15.5% of the impacts were associated with mild to severe head impacts, respectively, although these impact severity scales are based on collegiate athletes, not high school athletes.[13]

When striking a mounted ATD head, taekwondo athletes were able to generate 9,756 ± 3,842 rad/sec2 and 10,927 ± 8,017 rad/sec2 using a hook kick and turning kick respectively.[16]

The suggested tolerable reversible brain injury level for rotational acceleration is less than 6,000 rad/sec2.[19] The majority of blows measured during live sparring matches would be considered below the injury threshold; however, at least 15.5% of the measured blows were above 7,900 rad/sec2, which is well above this injury threshold.[13] Both the average hook kick and average turning kick rotational accelerations as measured using the mounted head resulted in rotational accelerations significantly above this threshold.[16]

Though rotational acceleration is not as well characterized as linear acceleration in the current literature, it is suggested that future studies should include measurements of rotational acceleration as it relates to head injury severity.[17]

Table 2: Comparing measured rotational acceleration from various taekwondo studies
Paper Strike Rotational acceleration (rad/sec2) ATD Headform Used
O'Sullivan and Fife, 2017[13] Live sparring sessions 4,726 ± 1,931 Live sparring - no ATD
Fife et al., 2018[16] Hook kick 9,756 ± 3,842 Hybrid III
Turning kick 10,927 ± 8,017

Head Injury Criterion

Head injury criterion is a measure of the likelihood of sustaining a head injury after an impact. HIC is commonly used to assess potential injury, specifically risk of concussions, during contact sports such as taekwondo over a 15-ms time window.[15] There is a large range in HIC depending on the type of kick used, ranging from a mean of 56.88 ± 54.87 for a front axe kick to a mean of 672.74 ± 40.89 for a turning kick.[15][18] The maximum HIC measured in this study was 1,016.4 which is significant considering a HIC of 1,032 was reported as the threshold for severe neurological injury with an Abbreviated Injury Scale (AIS) score of 5.[15][18][20] The mean HIC measured by Fife et al. was 442.62, measured across five different types of kicks commonly used in taekwondo, which is just under the threshold of 533 for moderate neurological injury, AIS between 3 and 4.[15][20] These studies are limited because the measurements are taken using a mounted head-form and therefore may not be an accurate representation of real-life HIC from taekwondo matches.

In the same study used earlier, head injury criterion was assessed during sparring matches between high school athletes. Male taekwondo athletes achieved a HIC of 35 ± 130, significantly lower than those measured using the head-form; however, this trend is consistent for linear and rotational accelerations as well.[13] The suggested injury tolerance level for HIC for tolerable reversible brain injury is estimated to be 240, which is greater than any of the forces recorded during live sparring sessions.[13][19]

Paper Strike Head Injury Criterion ATD Headform Used
Fife et al., 2013[18] Roundhouse 672.74 ± 540.89 Hybrid II
Front axe 56.88 ± 54.87
Clench axe 162.63 ± 104.10
Jump spinning hook 300.19 ± 144.35
Jump spinning back 462.95 ± 556.72

Effects of Protective Headgear

Given these HIC and acceleration values and in an effort to improve athlete safety, headgear was introduced into the sport of taekwondo in 1985 in an attempt to reduce these values.[21] The efficacy of this headgear is evaluated by testing the attenuation properties of the materials in a competition-like setting and resulted in the following standards being set.[21] Performance requirements according to the American Society for Testing and Materials (ASTM) guidelines state that the maximum linear acceleration measured due to a high energy striking impact test (144 J) cannot exceed 150g, the retention system must remain intact and the headgear must remain on the headform for the duration of the impact testing.[22]

An evaluation of commonly used taekwondo and boxing protective headgear found that these headgear fail to pass the ATSM criterion to reduce head accelerations below 150g, and the headgear failed to attenuate rotational accelerations to below the possible concussion thresholds of 6,000 rad/sec2.[19][21][22] This study also determined that the thickness of the headgear padding did not correlate to attenuation properties and that other features, such as material properties, are important to explore while trying to optimize headgear.[21]

Problems and Controversies

Even though extensive studies have been conducted in the area of taekwondo head impact, there are many shortcomings in these studies including the type of ATD used, the biomechanical parameters measured, and the efficacy of the methodology used.

In 2013, Fife et al. conducted a study to measure linear acceleration using an instrumented Hybrid II 50th percentile crash test dummy.[15] The use of a Hybrid II dummy is one shortcoming of this study as it is not as biofidelic as its successor, the Hybrid III. The Hybrid II’s response corridors do not completely fall within the postmortem human surrogate (PMHS) biomechanical responses. Additionally, the neck of the Hybrid II is much more rigid and simplified thus, does not represent the full biomechanical capabilities of the human head and neck.[15] Another limitation of the study is the comparison of only linear acceleration values against Olympic boxing punches and the inference that the linear head acceleration due to taekwondo kicks is higher, thus more dangerous.[15] Although linear acceleration is a good predictor of concussions, there are many other factors to consider. Rotational acceleration is an important factor to consider as a potential predictor of concussions because such accelerations can cause shear strain between the brain and cranial connective tissues, and therefore could cause concussions.[15]

Following the previous study Fife et. al addressed these shortcomings by conducting a study in 2018 that compared the efficacy of linear and rotational acceleration using an instrumented Hybrid III 50th percentile crash test dummy.[16] In this study, univariate and multivariate statistical analyses were performed however, the authors were unable to delineate the importance of rotational acceleration compared to linear acceleration.[16] Therefore, it is unclear at this time the impact that rotational acceleration has on brain injuries in comparison with linear acceleration. This controversy between the comparison of linear and rotational acceleration is quiet prevalent in the literature and among professionals sports organizations.[23][24] Various articles state that angular acceleration is believed to cause more damage to the brain than linear acceleration during an impact although both occur simultaneously, however; this study was unable to prove that.[24][25]

Efforts to explore the significance of various other factors and injury criteria have also been conducted, including a 2017 in-vivo study involving male high school taekwondo athletes and the use of the X Patch, a wearable accelerometer and gyroscope sensor.[13] One of the drawbacks of this study is the reliability of the collected data. The authors cite a study that reports that the X-Patch overpredicts linear acceleration data with 120% of normalized root square error and 290% of normalized root square error for rotational acceleration.[13] However, an additional study is cited that reports underestimation of the rotational acceleration data.[13] Therefore, there is an uncertainty in the reliability of the collected data in this study.

To eliminate any subject and device errors used in the laboratory, a computer simulation is used in one of the studies by Boroushak et al. (2018) to simulate a taekwondo roundhouse kick to the head.[14] A neck and body assembly was simulated using a clamped free beam system with parameters to simulate the human response.[14] However, this study only measured the biomechanical parameters such as peak and average linear and rotational accelerations respectively without quantifying these parameters to predict brain injury. A claim is made by the authors that this study’s results are more accurate than those conducted in the laboratory however, no injury criterion was analyzed to determine the effectiveness of this simulation.[14] Therefore, it is unclear whether these results are indeed more accurate than those obtained through the Fife group studies.

Future Work

In recent years there has been much attention from North American media regarding the occurrence of head injuries in popular sports such as American football. In 2016, the National Football League announced that they would be dedicating $100 million USD towards initiatives focused on researching the effects of head injuries in the NFL and the development of new technology to reduce the risk of head injuries occurring during games.[26] Unfortunately, even though the occurrence of concussions in taekwondo is between two to four times higher than in American football, head injury biomechanics research in taekwondo remains scarce due to a lack of sufficient funding.[18][27] Because of this lack of funding there is still much work to be done in order to expand upon the current understanding of head impact injuries in taekwondo.

One potential area for improvement involves the implementation of modern technology in taekwondo injury studies to allow for more thorough data collection such as the Head Impact Telemetry System (HITS). HITS is a hardware and software based system which combines video tracking with a device made up of 6 single-axis accelerometers which can fit inside headgear.[28] This system enables real-time monitoring of the kinematics and locations of head impacts during a live match.[28] Since the HITS system uses video tracking it can provide better insight on the accuracy of detecting impacts than the X patch used in previous studies. HITS devices have previously been used to study a range of sports including American football, ice hockey, soccer, boxing, and snow sports, but they have never been used to study taekwondo.[29] Future work which makes use of this technology will be able to more accurately assess the occurrences of head injuries in taekwondo athletes.

Furthermore, there has been very limited large-scale research into the long-term effects of head trauma in taekwondo. Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease that is linked to repeated brain trauma and is characterized by cognitive and behavioral symptoms such as memory impairment, mood swings, and increased aggression.[30] Advanced cases of CTE will also always lead to dementia.[30] It is currently unknown exactly what level of trauma will lead to CTE. Furthermore, CTE can only be diagnosed post-mortem.[30] Although CTE has been documented amongst boxers there have not been any long-term studies looking into the occurrence of CTE in taekwondo athletes.[30] Impacts to the head are a core component of taekwondo and the frequency at which taekwondo athletes suffer blows to the head suggests that occurrences of CTE are likely. Although CTE can only be diagnosed post-mortem there are current researchers that may be close to a living diagnosis.[31] In the absence of this, there are a progression of symptoms throughout an individual’s life that can help narrow down a diagnosis of CTE.[30] Thus, a large-scale study could be performed looking at retired taekwondo athletes and screening for these symptoms to reveal that CTE is common among these athletes. With this information a potential solution could be implemented to reevaluate the scoring system of taekwondo to disincentivize repeated hard head impacts.

Implementing the changes mentioned above into the field of taekwondo injury biomechanics research will greatly increase the scientific community’s understanding of the risks associated with taekwondo and will allow athletes to more safely practice the sport in the future.

References

  1. ↑ 1.0 1.1 Koh, Jae; Watkinson, E Jane; Yoon, Yong-Jin (2004). "Video analysis of head blows leading toconcussion in competition Taekwondo". Brain Injury. 18 (12): 1287–1296. doi:https://doi.org/10.1080/02699050410001719907 Check |doi= value (help).
  2. ↑ Zemper, E.D.; Pieter, W. (October 1998). "Cerebral concussions in Taekwondo athletes". Journal of the Royal Society for the Promotion of Health. 118 (5): 272–279. doi:10.1177/146642409811800512.
  3. ↑ Koh, J.O.; De, Freitas T; Watkinson, EJ (2001). "Injuries at the 14th World Taekwondo Championships in 1999". International Journal of Applied Sports Sciences. 13.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 Moenig, Udo (2015). "Rule and equipment modification issuesin World Taekwondo Federation (WTF) competition". Journal of Martial Arts Anthropology. 15 (4): 3–12. doi:10.14589/ido.15.4.2.
  5. ↑ "Competition Rules & Interpretation" (PDF). 2022. |first= missing |last= (help)
  6. ↑ 6.0 6.1 6.2 Ha, Sunghe; Kim, Min Jin; Hee, Seong Jeong (2022). "Mechanisms of Sports Concussion in Taekwondo: A Systematic Video Analysis of Seven Cases". International Journal of Environmental Research and Public Health. 19 (16): 10312. doi:https://doi.org/10.3390/ijerph191610312 Check |doi= value (help).
  7. ↑ Emery, Carolyn; M Black, Amanda; Kolstad, Ash (2017). "What strategies can be used to effectively reduce the risk of concussion in sport? A systematic review". British Journal of Sports Medicine. 51 (12): 978–984. doi:10.1136/bjsports-2016-097452.
  8. ↑ 8.0 8.1 deWeber, Kevin; Parlee, Lindsay; Lenihan, Michael; Nguyen, Alex; Goedecke, Leah (June 13, 2023). "Headguard Use in Combat Sports: Position Statement of the Association of Ringside Physicians" (PDF). Association of Ringside Physicians. Retrieved November 24, 2023.
  9. ↑ 9.0 9.1 Committee on Sports-Related Concussions in Youth; Board on Children, Youth, and Families; Institute of Medicine; National Research Council; R. Graham, F. P. Rivara, M. A. Ford, et al., editors. “Consequences of repetitive head impacts and multiple concussions” in Sports-related concussions in youth: Improving the science, changing the culture. National Academies Press, 2014. Available from https://www.ncbi.nlm.nih.gov/sites/books/NBK185336/
  10. ↑ 10.0 10.1 10.2 10.3 10.4 10.5 Koh, Jae O; Cassidy, J. David. (2004). “Incidence study of head blows and concussions in competitive Taekwondo.” Clin J Sport Med, 14 (2):72-79. doi:10.1097/00042752-200403000-00004
  11. ↑ 11.0 11.1 11.2 11.3 11.4 11.5 11.6 Koh, Jae O; Voaklander, Don. (2016). “Effects of competition rule changes on the incidence of head kicks and possible concussions in Taekwondo.” Clin J Sport Med, 26 (3): 239-244. doi: 10.1097/JSM.0000000000000244
  12. ↑ 12.0 12.1 Kim, Hye-Jin; Koh, Jae-Ok. (2022). Possible concussions related to a direct head kick among college Taekwondo athletes. Exercise Science, 31 (2): 230-237. doi: https://doi.org/10.15857/ksep.2022.00087
  13. ↑ 13.00 13.01 13.02 13.03 13.04 13.05 13.06 13.07 13.08 13.09 13.10 13.11 13.12 13.13 13.14 13.15 13.16 O'Sullivan, David M; Fife, Gabriel P. (2017). "Biomechanical head impact characteristics during sparring practice sessions in high school taekwondo athletes". JNS Pediatrics. 19 (6): 662–667. doi:10.3171/2017.1.PEDS16432. line feed character in |title= at position 49 (help)
  14. ↑ 14.0 14.1 14.2 14.3 14.4 14.5 14.6 Boroushak, Neda; Eslami, Mansour; Kazemi, Mohsen; Daneshmandy, Hasan; Johnson, John A. (2018). "The dynamic response of the taekwondo roundhouse kick to head using computer simulation". Journal of Martial Arts Anthropology. 18 (2): 54–60. doi:10.14589/ido.18.2.8.
  15. ↑ 15.00 15.01 15.02 15.03 15.04 15.05 15.06 15.07 15.08 15.09 15.10 15.11 15.12 15.13 Fife, Gabriel P.; O'Sullivan, David M.; Pieter, Wily; Cook, David P.; Kaminski, Thomas W. (2013). "Effects of Olympic-style taekwondo kicks on an instrumented head-form and resultant injury measures". British Journal of Sports Medicine. 47 (18): 1161–1165. doi:10.1136/bjsports-2012-090979. line feed character in |title= at position 47 (help)
  16. ↑ 16.00 16.01 16.02 16.03 16.04 16.05 16.06 16.07 16.08 16.09 16.10 16.11 Fife, Gabriel P.; O'Sullivan, David M.; Lee, Sae Yong (2018). "Rotational and linear head accelerations from taekwondo kicks and punches". Journal of Sports Sciences. 36 (13): 1461–1464. doi:https://doi.org/10.1080/02640414.2017.1398406 Check |doi= value (help). line feed character in |title= at position 46 (help)
  17. ↑ 17.0 17.1 17.2 17.3 O’Sullivan, David; Fife, Gabriel; Pieter, Willy; Lim, Taehee; Shin, Insik. (2016). “Resultant linear acceleration of an instrumented head form does not differ between junior and collegiate Taekwondo athletes’ kicks.” Journal of Sport and Health Science, 5 (2): 226-230. doi: https://doi.org/10.1016/j.jshs.2015.01.004
  18. ↑ 18.0 18.1 18.2 18.3 18.4 18.5 Fife, Gabriel; O’Sullivan, David; Pieter, Willy. (2013). “Biomechanics of head injury in Olympic Taekwondo and boxing.” Biol. Sport, 30 (4): 263-268. doi: 10.5604/20831862.1077551
  19. ↑ 19.0 19.1 19.2 19.3 Zhang, Liying; Yang, King H; King, Albert I. (2004). “A proposed injury threshold for mild traumatic brain injury.” Journal of Biomechanical Engineering, 126 (2): 226-236. doi: 10.1115/1.1691446
  20. ↑ 20.0 20.1 Marjoux, Daniel; Baumgartner, Daniel; Deck, Caroline; Willinger, Remy. (2008). “Head injury prediction capability of the HIC, HIP, SIMon and ULP criteria.” Accident Analysis & Prevention, 40 (3): 1135-1148. doi: 10.1016/j.aap.2007.12.006
  21. ↑ 21.0 21.1 21.2 21.3 O’Sullivan, David; Fife, Gabriel. (2016). “Impact attenuation of protective boxing and Taekwondo headgear.” European Journal of Sport Science, 16 (8): 1219-1225. doi: 10.1080/17461391.2016.1161073
  22. ↑ 22.0 22.1 American Standards for Testing and Materials. (2004). “Standard specification for protective headgear used in martial arts (F 2397-4).” West Conshohocken, PA USA.
  23. ↑ Rush, Beth (Springer). Encyclopedia of Clinical Neuropsychology. New York. pp. 2196–2197. ISBN 978-0-387-79948-3. Check date values in: |year= (help)
  24. ↑ 24.0 24.1 King, Albert I.; King H., Yang; Zhang, Liying; Hardy, Warren; Viano, David C. (September 2003). "Is Head Injury Caused By Linear or Angular Acceleration?" (PDF). IRCOBI Conference – Lisbon (Portugal).
  25. ↑ Lota, Kabir Singh; Malliaropoulos, Nikos; Blach, Wiesław; Kamitani, Takeshi; Ikumi, Akira; Korakakis, Vasileios; Maffulli, Nicola (2022). "Rotational head acceleration and traumatic brain injury in combat sports: a systematic review". British Medical Bulletin. 141 (1): 33–46. doi:https://doi.org/10.1093/bmb/ldac002 Check |doi= value (help).
  26. ↑ Belson, Kyle (Sep. 14, 2016). "N.F.L. to Spend $100 Million to Address Head Trauma". The New York Times. Check date values in: |date= (help)
  27. ↑ Pieter, Willy; Fife, Gabriel P.; O'Sullivan, David M. (2012). "Competition Injuries in Taekwondo: A Literature Review and Suggestions for Prevention and Surveillance". British Journal of Sports Medicine. 46(7): 485–491. doi:10.1136/bjsports-2012-091011. Check |doi= value (help).
  28. ↑ 28.0 28.1 Campbell, Kody R.; Marshall, Stephen W.; Luck, Jason F.; Pinton, Gianmarco F. (2020). "Head Impact Telemetry System's Video-based Impact Detection and Location Accuracy". Medicine & Science in Sports & Exercise. 52(10): 2198–2206. doi:10.1249/MSS.0000000000002371.
  29. ↑ O'Connor, Kathryn L.; Rowson, Steven; Duma, Stefan M.; Broglio, Steven P. (2017). "Head-Impact–Measurement Devices: A Systematic Review". Journal of Athletic Training. 52(3): 206–227. doi:10.4085/1062-6050.52.2.05.
  30. ↑ 30.0 30.1 30.2 30.3 30.4 Lim, Lucas J. H.; Ho, Roger C. M.; Ho, Cyrus S. H. (2019). "Dangers of Mixed Martial Arts in the Development of Chronic Traumatic Encephalopathy". International Journal of Environmental Research and Public Health. 16(2): 254. doi:10.3390/ijerph16020254.
  31. ↑ Belson, Ken (November 17, 2022). "A Test for C.T.E. in the Living May Be Closer Than Ever". The New York Times.
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