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Epidemiology of injuries in juniors participating in top-level karate competition: a prospective cohort study
  1. Dušana Čierna1,
  2. Merce Barrientos2,
  3. Carlos Agrasar2,
  4. Rafael Arriaza2,3
  1. 1Faculty of Physical Education and Sports, Comenius University, Bratislava, Slovakia
  2. 2Physical Education and Sports School, Universidade da Coruña, A Coruña, Spain
  3. 3Instituto Médico Arriaza y Asociados, HM Sports Traumatology Chair, Universidade da Coruña, A Coruña, Spain
  1. Correspondence to Dušana Čierna, Faculty of Physical Education and Sports, Comenius University in Bratislava, Nábrežie armádneho generála Ludvíka Svobodu 9, Bratislava 814 69, Slovakia; cierna.dusana{at}gmail.com

Abstract

Background Karate is a popular combat semi-contact sport among juniors, but there are only few studies available on the epidemiology of injuries in karate junior athletes.

Aim The aims of this study were to determine the incidence and pattern of injuries in top-level karate competition for athletes aged 16 to 20 years, and to compare injury rates between age groups (ie, under 18-year-old [U18] and under 21-year-old [U21]) and genders, following the introduction of new weight categories.

Methods A prospective injury surveillance was undertaken at four consecutive World Karate Championships (2009 to 2015), following the same protocols used in previous investigations.

Results During the four championships, a total of 257 injuries were recorded, with an incidence of 41.4/1,000 athlete exposures (AEs, 95% CI 36.4 to 46.3). The injury rate was significantly lower for females with a rate ratio 0.63 (95% CI 0.48 to 0.82). Most of the injuries were minor ones: contusions (n=100), followed by abrasions (n=63) and epistaxis (n=62). Only 10% of the injuries were time-loss injuries (injury incidence rates 4.2/1,000 AEs; 95% CI 2.7 to 6.1). Face injuries represented 69.6% of the injuries, most of them were minor ones (light abrasions 24.5%, epistaxis 24.1%, contusion 16.7%). Change of rules (raising the number of weight categories from three to five) reduced injury incidence in the U21 category.

Conclusions The total injury rate in junior competitions is lower compared with elite adult athletes and higher compared with younger elite athletes. Time-loss injuries are rare. The implementation of the new competition categories in U21 karate has been associated with a significant reduction in injury rate.

  • martial arts
  • injuries
  • risk factor

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Introduction

Karate is a popular martial art with increasing participation of children: in some regions of the USA, enrolment of children in martial arts such as karate more than doubled during the past decade.1 Presumably this number will increase even more after the inclusion of karate into the group of sports for the Olympic Games in Tokyo 2020 and the Youth Olympic Games in Buenos Aires 2018. Karate can induce numerous benefits (health, self-defence, self-confidence, etc.), concurrently provoking a risk of injury. Therefore, it is necessary to investigate the safety of karate as a sport and during competition specifically.

The competition of karate is divided into forms or ‘kata’, and combat or ‘kumite’. During the kata competition, athletes perform pre-arranged techniques individually, and no risk of accidental contact exists. During kumite competition, two athletes are engaged in a semi-contact striking fight, where the athletes run the risk of unwanted excessive contact that might cause injury to the opponent, or even to themselves. In Olympic or World Karate Federation (WKF) karate, rules award points only for controlled punches and kicks to head and body that do not cause injury to the opponent.

During Olympic karate competition, contestants wear protective equipment homologated by WKF: mitts, body protector, shin pads, foot protection and a gum shield are mandatory (plus chest protector for female athletes). Also for under 18 year-old (U18) competition, rules are more strict about prohibited behaviour for athletes, including excessive force used in blows to permitted areas, and enforcing penalties for attacks to forbidden areas (throat, arms, legs, groin, joints and instep), blows to the face with open hand techniques and dangerous or prohibited throwing techniques. Any illegal behaviour results in a warning or penalty. For under 21-year-old (U21) athletes, non-injurious, light and controlled contact to the face, head and sides of the neck is allowed (but not to the throat), which makes control of the techniques and attacks performed paramount, but gives rise to the possibility of unwanted accidents.

In WKF kumite competition, athletes are divided by gender and by weight categories. In U18 competition, since the inception of the World Championships, there have been five weight categories for male athletes and there were four weight categories for female athletes: in 2015, the number of female weight categories was increased to five in the U18 category. In the U21 competition, initially there were only three weight divisions, but the increasing number of entries forced the organising committee of the WKF to increase the number of weight divisions in 2015 from three to five, both in male and female athletes.2 This fact allowed us to compare the possible effect of this increase in the number of weight divisions in the injury rate by analysing the championships separately.

The study of Destombe et al3 among national and international level athletes revealed a higher risk of injury during competition than during training, both in karate and in other combat sports. It is important to note that most of the studies were done retrospectively and before many of the rules changes that have been accomplished in the past 15 years aiming to reach higher safety in WKF karate competition.4

Only a few prospective studies on karate injuries included young athletes,5–8 and only two of them were dealing with young top-level athletes younger than 15 years.7 8 Some studies concentrated on injuries occurring either during training,5 9 or during national level competition.9–14 There are also published studies investigating injuries in different karate styles,10 or globally in martial arts.5 However, there is a greater number of studies dealing with injuries in adults.9–17 Some studies show that top-level (ie, World Championships) competitions run under WKF rules2 have lower injury rates7 15 16compared with national competitions or other full contact sports.18–21 These varying risks could be caused by the different rules of competition used in different karate styles and other martial arts.

The primary aim of this study was to determine the incidence and pattern of injuries in top-level karate competition for athletes aged 16 to 20 years. The secondary aim was to compare injury rates between the different age groups (ie, U18 and U21), both genders and also the effect of the introduction of new weight categories in 2015 on injury rates.

Methods

Study population

This prospective epidemiological cohort study included all male and female athletes participating in individual combat (in U18 and U21 age categories there is no open weight or team events) competition at four consecutive World Karate Championships held in 2009 (Rabat, Morocco), 2011 (Melaka, Malaysia), 2013 (Guadalajara, Spain) and 2015 (Jakarta, Indonesia). The athletes competed in one of two age categories: 16 to 17 years' old (U18), or 18 to 20 years' old (U21). In the U18 category, until 2015 female athletes competed in four, and male athletes in five, weight divisions. In the U21 category both male and female competitors were divided into three weight divisions until 2015. After a rule change in 2015, both female and male athletes compete in five weight divisions. Each bout in the U18 category and in the female U21 category lasted 2 min, while each bout in the male U21 category lasted 3 min.

Data collection

Data were collected prospectively using checklists following the same protocols used in previous investigations of injuries at World Karate Championships and published elsewhere.7 15–17 Collected data included: gender, age, weight category, injured body part, type of injury and injury severity (minor or time-loss injury). All injuries were diagnosed by official tournament sports medicine personnel. For each tatami (competition area), there was one doctor plus one assistant. As the World Karate Championships are held every 2 years in different locations, and in an effort to standardise data collection, before the commencement of each championship, the senior author, as Chairman of the Medical Commission of the WKF (R.A) instructed the official tournament sports medicine staff on the injury recording procedure. The quality of the recorded data was reviewed three times per day, to clarify any possible doubts and to ensure uniform injury classification. Whenever an injury was deemed as severe or potentially severe, athletes were referred to a nearby hospital for further diagnostic procedures, and feedback on the diagnosis was retrieved directly by the WKF Medical Commission Chairman. In this study all recorded injuries were subsequently coded by a trained researcher using the Orchard Sports Injury Classification System, version 10 (OSICS-10).22

Operational definitions

An injury was defined as any physical complaint for which an athlete would seek assistance from tournament medical personnel. Injuries were categorised as non-time-loss or time-loss injury, where time-loss injuries are defined as injuries that prevent the athlete from completing the present bout and/or subsequent bouts and from participating in sport activities for a minimum of 1 day thereafter.23

One athlete exposure (AE) refers to one individual athlete participating in a bout where he or she is exposed to the possibility of being injured, which means that for each bout, there are two AEs. One minute of exposure refers to 1 min of fighting per one individual athlete in a bout.

Data analysis

As the duration of the combats was different in U18 and U21 females than in U21 males divisions, injuries were analysed considering both AEs and minutes of exposure to risk. Injury incidence rates (IIRs) per 1000 AEs and per 1000 min of exposures (MEs) were calculated using standard methods. Subgroups were compared by computing the rate ratio (RR) of two IIRs. Ninety-five per cent confidence intervals (95% CIs) were computed for all IIRs and RRs using standard formulae for Poisson rates.24 The 95% CIs for RRs were used to determine whether two IIRs differed significantly from one another, that is, two IIRs were deemed statistically different from one another if the 95% CI for their RR did not include the null value (ie, 1).

Confidentiality and ethics approval

Before entering the championships, athletes or their representatives signed the informed consent to allow for injury registration and treatment. The rules of the WKF state that before athletes are allowed to enter a championship, they have to be declared fit to compete by their local medical authorities. All authors followed the rules of the Helsinki Declaration and the Ethics Committee of A Coruña University approved the study (UDC EC 12/2016). The injuries were recorded, without any information that could allow identification of the athletes. No names or other personal information was registered to guarantee anonymity.

Results

Overall injury incidence rates

The number of athletes by age, gender and overall injury incidence rates can be found in table 1. A total of 257 injuries were recorded, with an incidence of 41.4 (95% CI 36.5 to 46.7) injuries per 1000 AEs. From the total of 257 injuries, only 26 (10%) were time-loss injuries with an incidence of 4.2 time-loss injuries per 1000 AEs (95% CI 2.7 to 6.1).

Table 1

Injury rates in juniors karate athletes (overall data from all championships)

Injury risk

The overall injury rate was significantly lower for females than males (RR for AEs 0.6; 95% CI 0.5 to 0.8; RR for MEs 0.7; 95% CI 0.5 to 0.9; table 1).

Out of the 257 injuries, 125 were recorded in U18 categories, with an incidence of 36.4 (95% CI 30.3 to 43.4) injuries per 1000 AEs, and 132 in U21 categories, with an incidence of 47.5 (95% CI 39.8 to 56.4) injuries per 1000 AEs. The injury incidence rate was significantly lower for U18 than for U21 with a RR for AEs of 0.8 (95% CI 0.6 to 1.0) and RR for MEs 1.0 (95% CI 0.8 to 1.3).

Injury rate in U21 categories was higher when competition was run with three weight categories (IIR 61.4; 95% CI 50.7 to 73.7 per 1000 AEs), than when the number of weight categories was increased to five in the year 2015 (IIR 18.8; 95% CI 10.9 to 30.0 per 1,000 AEs), with a RR for AEs of 0.3 (95% CI 0.2 to 0.5) and RR for MEs 0.3 (95% CI 0.2 to 0.4).

When analysing championships separately, it became evident that the number of injuries decreased after 2015 when compared with the previous championships (table 2).

Table 2

Injury rates in U18 and U21 categories by championships

Common injury types

Most of the injuries were contusions (n=100, 38.9%), followed by minor abrasions (n=63, 24.5%) and epistaxis (n=62, 24.1%). Face injuries represented 69.6% of the injuries (n=179), although most of them were minor ones (light abrasions n=63, 24.5%; epistaxis n=62, 24.1%; contusion n=43, 16.7%; laceration n=6, 2.4%; nose fracture n=5, 1.9%). The distribution of all injuries is shown in table 3.

Table 3

Frequency and proportion of injuries by anatomical location

Discussion

The main finding of this study is that the risk of injury to the juniors athletes involved in top-level Olympic karate competition is 41.4 (95% CI 36.41 to 46.31) per 1000 AEs, and that nine out of 10 were minor injuries. There were not any catastrophic injuries. Based on these findings we can conclude that when the rules of WKF are followed and proper protection is used, injuries in junior athletes participating in karate competition are infrequent.

Female athletes had a lower risk of injury than their male counterparts, and not unexpectedly, injury rate was lower in the U18 than in the U21 category. The finding that the injury rate was lower in the U18 category could probably be explained by the fact that WKF competition rules limit face contact to a greater extent in this category than in the U21 one.

Determination of injury risk is done in several different ways, but usually, time of exposure (in team sports it is measured as hours or number of injuries per 1000 hours) and AEs are the two denominators most commonly found in the literature.25 In our study, we measured the risk in terms of injuries per 1000 min of exposures (as in individual combat sports the length of the bouts is very short) and per athlete exposures, to obtain data that could be used for comparison with other sports or even within karate if the length of the fights changes in the future.

Injury risk depends on age and skill level

Although intuitively it could be considered that athletes with a lower level of training and technique control could have more injuries, some studies reported that higher skilled athletes had more injuries, maybe because they are potentially more likely to use dangerous offensive and defensive techniques or execute fundamental ones with greater strength and speed.5 The same has been shown also in other sports, e.g. in soccer.26 Our study confirmed this, as the rate of injuries was significantly higher for U21 than for U18 categories.

Comparison with other karate and combat studies

We have found a higher number of injuries per 1000 AEs compared with Arriaza et al7 in cadet category (14–15 years' old) in their study. They found 29.9 injuries per 1000 AEs, while in our study there were 41.4/1000 AEs. It should be noted that cadets wear protective face masks that are not used in the age categories included in our study. The rest of the protective equipment is identical in all categories. For cadets (U15) and (U18) categories, competition rules are stricter than in the U21 category regarding the amount of contact allowed during competition. To increase protection in the U15 category, no touch or contact to the head, face or neck, (including the face mask) is allowed with hand techniques. Any touch or contact, no matter how light, is penalised.2 In seniors' categories, the rate of injuries found in a previous study15 is higher, reaching 180 injuries per 1000 AEs, which represents approximately 77% more than was found in our study, but we must bear in mind that this data was found before the change in the WKF competition rules that reduced the injury rate by half.16 This fact might also explain the difference in injury rates found in taekwondo, in the meta-analysis form Lystad et al, where the injury rate was 79.3 per 1,000 AEs, without significant differences from age, gender or level of play, but studies were pooled without attending to possible changes in competition rules.27 The rate of injuries in our study was 41.4 per 1000 AEs, (95% CI 36.41 to 46.31), which is lower than those previously reported in karate by Tuominen (male IIR 115.1 per 1000 AEs, 95% CI 75.2 to 155.0 and female IIR 133.1 per 1000 AEs, 95% CI 87.7 to 178.5),14 Müller-Rath et al (IIR 190.5 per 1000 AEs, 95% CI 114.3 to 266.7)28 Macan (IIR males 80.3 per 1000 AEs 95% CI 49.4 to 111.1, female IIR 103.5 per 1000 AEs, 95% CI 20.7 to 186.2),29 and Arriaza and Leyes (IIR 157.0 per 1000 AEs; 95% CI 146.9 to 167.7),15 although similar to the one reported by Critchley et al (IIR 45.2; 95% CI 38.5 to 52.8).10 Higher number of injuries in senior categories was recorded by some authors, although other have found no difference related to the age of the participants,29 but again, we must take into consideration the different competition rules that have been used in the past by WKF and that are still in use in other karate modalities.

In the age groups included in our study, we have to consider also the possibility of coaches pressurising young athletes to win a medal at an important event.30 Coaches may lead their athletes to unsafe or excessively aggressive tactics. An important role in the prevention of this situation may be played by referees. Referees are essential in the regulation of the flow of the bout. Moreover, their communication with medical teams is crucial in order to define the severity of injuries (whether real or feigned injuries), as injury simulation implies a penalisation, or even disqualification, to the athlete that tries to confound the referees.

In our study, head and face were the most frequently injured areas, similar to other studies.9–11 14 This could be explained by the fact that top-level karatekas perform more technical actions aimed to the head (79.1%±15.1%) than to the body (20.9%±15.1%).31 The results presented by Zetaruk et al5 show that most injuries sustained during training were localised to the extremities which might be explained by the use of different rules during sparring at training and competition.

Comparison with other sport studies

In our study female athletes had significantly lower injury risk than males. Some studies have shown a higher injury incidence in male athletes.14 32 On the contrary, other studies on injuries in karate,6 29 soccer26 and judo athletes21 have found a higher incidence of injuries in female participants. Although no clear explanation can be given to this discrepancy in injury rates between male and female athletes in different studies, we may hypothesise that both weight divisions and competition rules used in Olympic karate offer a greater protection to female athletes than in other combat sports competition.

Contrary to what has been found in studies on judo,33 wrestling18 or American football,34 there have been no catastrophic injuries recorded in any karate study. During the time span of our study throwing and projections were allowed by the competition rules, but contrary to some other sports, those techniques could only be performed below waist level and while holding the opponent to control the fall, which could explain a lower risk of accidents involving falls on the head.2

Some authors have found that risk of injury in karate and martial arts has increased,4 7 32 but we have recorded a decrease in the number of injuries during the 6- year span of our study, which may be attributed to the changes in competition rules, such as the increase in the number of weight divisions in the U21 category. In general, WKF or Olympic karate does not seem less safe than other sports. According to Tenvergert et al, injury risk in soccer (59.2/100 athletes) was four times higher than in volleyball (16.7/100 athletes) and gymnastic (14.9/100 athletes), and six times higher than among martial art athletes (9.1/100 athletes/year) (p<0.0001).35

The impact of the study

When comparing these studies there should be taken in consideration that previous studies used different methods of data gathering and analysis, and that different karate styles may use different competition rules and that even within Olympic karate the rules of competition evolve and those changes may have an impact on injury risks. Also, there could have been differences in the evaluation of the severity of some injuries by different authors. We consider that it is important to notice, on the one hand, the fact that some apparently minor changes in the competition rules, as it might be simply changing the weight categories, might have an important change in the safety of the athletes, and on the other, that only by continuous, prospective recording of the injuries it will be possible to identify those changes to react properly if they take place. The injury recording system that we have set as compulsory for all the WKF events has proven to be inexpensive and feasible, as it does not requires any extra staff and provides invaluable information. We will try to expand it in the future to all the official karate tournaments in every continent and national federations affiliated to the WKF.

Limitations

This study only included data from the World Karate Championships organised by WKF, which may limit the generalisability of the findings, however all injuries were diagnosed by qualified health professionals, which gives the study a robust basis. This is one of the first large studies on young high-level karate athletes. We did not record injury severity in terms of the number of days that have elapsed from the date of injury to the date of the athlete’s return to full participation in training and match play. We did not record injury mechanisms. The findings reported in this study should be interpreted in the light of these limitations.

Conclusions

Our prospective study of top level karate competition in juniors found an injury incidence of 41.4 injuries per 1000 AEs, which is lower than among high-level adult karate athletes, and lower compared with young elite athletes from other martial arts and sports. Besides the fact that injury incidence is low the injuries that were recorded are of minor severity, and time-loss injuries are rare.

The method of gathering data on karate injuries presented in our study could help towards a more systematic approach in injury prevention. Having a standardised method of injury recording may allow comparison with other sports and evaluation of the effect of future rule modifications within karate.

What are the new findings?

  • Only one out of each ten injuries sustained in 16 to 20 year old top-level karate athletes are time-loss injuries.

  • Global injury rates in 16 to 20 year old athletes engaged in top-level competition are low, with an incidence of 41.4 injuries per 1000 athlete exposures (95% CI 36.4 to 46.3).

  • Injury risk for 16 to 20 year old top level female karate athletes is lower than for their male counterparts.

How might it impact on clinical practice in the near future?

Knowledge of the injury risk of top-level karate competition for athletes between 16 and 20 years of age will allow the setting of a baseline to compare other competition levels and age frames of the same sport and to analyse the impact of future changes of competition rules on the safety of the sport.

Acknowledgments

The Medical Commission of WKF is thanked for its support and co-operation.

References

Footnotes

  • Contributors DC: substantial contributions to conception and design, literature search analysis and interpretation of data; drafting the manuscript and revising it critically for important intellectual content; and final approval of the version to be published.MB: Substantial contribution to conception and design of the article, literature search and data interpretation, and final approval of the version to be published. CA: Substantial contribution to conception and design of the article, literature search and data interpretation, and final approval of the version to be published. RA: Conception and design of the article; literature search; data collection; revising the manuscript critically for important intellectual content; and final approval of the version to be published.

  • Funding None.

  • Competing interests None declared.

  • Ethics approval Ethics Committee of A Coruña University, Spain.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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