Sparring-Taekwondo (S-TKD) is a full-body contact sport that has been an official sport of the summer Olympic games since 2000 when it gained the additional name of Olympic-style taekwondo. Attacks and counter-attacks for all types of taekwondo permit the legal scoring of kicking techniques directed toward the head/face/neck (i.e., head kicks) and torso, though punching the head region is illegal. Given the kicks used in S-TKD, there is a high risk for brain and musculoskeletal injury in competition and training sessions. A number of studies have reported injury rates in S-TKD competitions [1–9]. In one report, 1,466 injuries occurred in 283 athletes during training, with an average of 5 injuries per athlete annually [10]. A meta-analysis found an injury rate of 79 per 1,000 athlete-exposures (A-E) in taekwondo competitions [6]. Similarly, a recent study of an S-TKD team from Korea has reported injury incidence rates in training sessions and competition of 5 and 25 per 1,000 A-E, respectively [9].

In addition to the musculoskeletal injuries in S-TKD, there is a high risk of concussion, ranging was from 0.0 to 50.2 per 1,000 A-E [11] which is anticipated since a direct kick to the opponent’ s head region is legal and promoted by the competition rule. Additionally, changes made by the sport’ s governing bodies (i.e., World Taekwondo (WT) and Korea Taekwondo Association (KTA) include a recent competition rule (i.e., 2018) where a valid head kick (HK) will be awarded from a minimum of 3 points to a maximum of 5 points (i.e., given higher points). As a result, the head zone has become a major scoring area since 2009. In 2019, the protective scoring system (PSS) was adopted in the competition taekwondo.

Changes to the scoring system for the HK have raised concerns regarding the increasing frequency of HKs and concussions in S-TKD [12–14]. Several epidemiological and biomechanical studies on head impact have been conducted over the last 10 years. Video analyses have con-firmed that the frequency of HKs has increased up to 40% when compared with a study done in 2002 (i.e., when all types of valid HK received 1 point) among youth and elite S-TKD athletes [12–16]. Although there are insufficient studies, follow-up studies revealed that the incidence rates of HKs and concussions seem increased (0.1%) among female high school athletes with no change in rates for male middle school athletes [15,17]. One biomechanical study measured the head impact frequency and magnitude over 6 TKD sparring training sessions involving 8 high school athletes [18]. The results showed that there was a total of 689 head impacts (24 impacts per 100 minutes), of which 97% were low or medium (range 10-69 g) and 3% were high (>69 g).

Since 2002 studies of S-TKD related concussions have been conducted exclusively with youth athletes. Studying S-TKD related head injuries in adults is important given the age groups of Olympic S-TKD athletes and professional S-TKD athletes yet studies for this group are limited. More-over, there is a high possibility of underestimating the incidence rate of concussions reported in the literature due to issues such as recall and selection bias. Sports-related concussion is not only an issue in S-TKD but also in other contact sports due to its short-term and long-term sequelae such as physical performance and neuropsychological problems or chronic traumatic encephalopathy (CTE) [19,20]. Therefore, the purposes of the current study are to estimate incidence rates of HKs and concussions with post-match interviews and to find possible risk factors associated with increased concussion rates among college S-TKD athletes in South Korea.

Because of a lack of studies on the risk of concussion in adult S-TKD athletes, the primary purpose of our study was to measure the true incidence of a concussion directly associated with an HK. We applied an in-terview-based prospective cohort design that allowed us to measure HK and concussion rates with less recall or selection bias. Specifically, S-TKD athletes’ self-reported injuries such as a concussion may be inaccu-rate due to misunderstanding regarding this injury. According to Koh’ s study [17], only 17% of TKD athletes understood they experienced a concussion and less than 10% of athletes experienced a concussion with loss of consciousness. Thus, the significance of this study is to establish an incidence rate of concussion in college competitors and measure the direct HK-related concussion risks among college athletes in S-TKD.

Overall, the incidence rates of HK and concussion were 175 HKs and 35 concussions per 1,000-A-E, respectively. There is clear evidence that the concussion rate has increased when compared to the Pieter and Zemper study [4] (overall, 5.5; male, 7.04; female, 2.42/1,000 A-E when awarding 1-point for an HK). Additionally, when we compared our injury rates to those of high school athletes who competed in 2001 [21], the incidence rate of HK has increased (175 vs. 141 HKs per 1,000 A-E), however, the rate of concussion has remained the same (35 vs. 35.9 concussions per 1,000 A-E). Also, when we compared only females’ incidence rates of HK and concussion to the female high school athletes who competed in 2018 [15] (i.e., HK=3-5 points), the rate of HK is higher (203 vs. 132 HKs per 1,000 A-E), but the rate of concussion is similar (45 vs. 44 concussions per 1,000 A-E). In another comparison to male middle school athletes [17], the present study shows a higher incidence rate of HK among the males (155 vs. 134 per 1,000 A-E). However, our concussion incidence rate is lower than that of middle school athletes (30 vs. 41 per 1,000 A-E). To summarize the differences among studies, there was the age difference, the level of competition, competition rule, and other potential factors such as the headgear sensor adaptation that may influence the present results.

The concussion risk for all HK recipients in the current study was 20.2% (female=22.2%; male=19.3%). When concussion risk is compared to the female high (33.3%) [15] and middle school (35.2%) [16] competitors, our college competitors have a lower rate than the adolescent competitors. Male middle school athletes show a similar trend (31%) [17]. In other words, when interviewing 100 athletes who receive an HK during the tournament, 22-35% of them are likely to occur a concussion.

According to our findings, female athletes recorded higher rates for both HKs and concussions than their counterparts, although the statistical failed to find a significant difference. One study [4] conducted prior to 2002 found results opposite to ours. However, the same results on gender differences of HK and concussion were found in the middle school players [16,17], but not in high school players [21]. A similar trend was observed from the video analysis of the elite level in S-TKD [14]. The high rate of HK-related concussions among females is likely due to females in our study favoring an axe kick which is relatively easy to exe-cute and effective to get high scores from the head kick point. However, a shift in this trend (i.e., an HK by an axe kick) was observed among male athletes in this study. These differences are likely due to changes in the point system for HKs since 2009 [12-14,23]. To verify the issue of gender differences, more research is required.

We did not find an association between a previous history of HKs and concussions and the present incidence rates. The same results were reported from another study with 51 high school female athletes [15]. In contrast, 154 middle school male athletes who had a previous history of concussion had a high incidence rate of concussion [17]. There are several possible reasons for such a discrepancy among studies. First, though there were no differences in study design, the age of research participants differed and the younger age group had a higher risk rate than the older age group [21]. Additionally, the sample size differed between studies, and unlike prior studies, the present study measured both genders. Furthermore, the number of matches per competition is greater in younger groups which results in a longer period of injury exposure which in-creases injury risk as well [21,22].

Two predictors for the increasing risk of concussions were discovered in the current study. Prior studies [15–17] have examined potential risk factors with conflicting results and these inconsistencies among studies remain unclear. Findings from the current study suggest that increased concentration by athletes on their opponent’ s movements during matches may decrease the likelihood of HK and concussion.

The most frequently executed kicking skill for the HKs was an axe kick, yet the most threatening kick that resulted in a concussion was a 360-spinning kick. The axe kick is noted as the most frequent kick in several studies [12-14,17,24]. The 360-spinning kick had a much lower frequency rate but was more likely to result in a concussion. Kicks using spinning techniques such as 360-spinning and roundhouse kicks have similarly been reported as a risk factor for concussions in other studies [15,17,24].

Among 22 athletes with concussions, 27% [6] complained of post-concussion symptoms. In the case of youth S-TKD, male middle school and female high school competitors had a higher rate of 36% [17] and 40% [15], respectively. Headache and dizziness were the most common symptoms. According to our results, the adult group may experience fewer post-concussion symptoms than younger age groups.

As noted previously, a number of athletes declined to participate which may have influenced the incidence rates of both HKs and concussions. Therefore, the reported incidence rates are likely lower than the actual rates in S-TKD tournaments. Also, the incidence rate of concussion was measured by a subjective questionnaire in this study. Additionally, as data collection is based on observation, there is a possibility of some missed cases. Given these limitations, the present injury rates can-not be generalized to all athletic competitions.

We found that 22 (20.2%) athletes experienced concussions among 109 HK recipients. The incidence rates of HK and concussion were high in our participants, with female athletes experiencing a higher frequency of HK and concussion than male athletes. However, these incidence rates may have been impacted by a number of athletes who declined to participate and data missed due to observer error. Nonetheless, the cur-

rent study provides further evidence that factors associated with the concussion rate include recognition of receiving an HK at the time of occurrence and the use of blocking maneuvers. Further research is necessary to confirm our observations, to monitor any changes in the concussion risk, to track cumulative negative effects of multiple HKs, and to provide a safer environment for future S-TKD athletes.