Type of injury and recovery time in elite adolescent Korean judo athletes: An epidemiological study

Abstract

We aimed to assess the risk of injury associated with training activities in a population of elite adolescent judo athletes, expected to represent South Korea. From 2019, we prospectively collected data on elite adolescent judo athletes at the Korean Training Center. The athletes were assessed by sports medicine doctors, and data were stratified according to sex, weight class, and injury location. We used χ² tests to compare groups. Injury rates were expressed as Poisson rates with 95% confidence intervals. One-way analysis of variance was used to investigate the pain score and recovery time due to type of injury. The study included 240 elite adolescent judo athletes whose 617 injuries (annual average, 2.57 injuries/athlete) were recorded. When all athletes were considered, most injuries occurred in the lower extremities (39.71%), followed by the upper extremities (36.63%), trunk (16.69%), and head and neck area (6.97%). Recovery time significantly differed according to the body regions in the weight classes. The pain score and recovery time according to the type of injury were significantly different. When the pain score decreased by 1, the recovery time decreased by about 1.47 days. In all weight classes, female athletes had a higher injury rate than male athletes; both male and female athletes had different recovery time depending on their weight class. The type of injury influenced the pain score and recovery time, with pain score being associated with recovery time.

Keywords

Combat sport,pain,sports medicine

Introduction

Judo is a martial arts event that includes the cultivation of the whole personality and physical training and has emphasized the mindset of the athletes compared to other sports events such as ethical morality. As a result, Judo training has pursued a humble attitude of developing the body in a healthy mind and caring for the other party.¹ Although the sport of judo being an individual and not a team sport, can have a negative effect on all the athletes simultaneously as they train and practice together as a whole for their own personal development.² Recent studies in the Summer Olympic Games also identified that a high percentage of competition injuries occurred in Judo.³ Other findings from epidemiology studies in judo revealed that the associated risk in judo may be as large as, that in team sports.^3–5

Generally, sports injury is associated with pain, which may limit athletes' participation in games and training⁶; thus, it is necessary to identify the degree of pain. Injuries that require a short-term recovery period and those that take longer time to recover from, cannot be seen identically.⁷ The seriousness of a sports injury affects not only the performance of the athletes but also the rate of injury, sensitivity, and recurrence.⁸ Currently, the International Olympic Committee (IOC) aims to develop a sports injury prevention program.³,⁴ There have been various studies of injuries in elite judo athletes.^9–11 However, only a few induction studies have focused on the relationship between weight class and injury. In addition, there is a lack of epidemiological studies on the degree of pain and recovery time due to sports injury; therefore, few prospective studies have aimed to identify and quantify risk factors for injury.^9–11 A proactive surveillance program has been launched in Korea targeting elite adolescent judo athletes who are expected to represent Korea in the future in order to collect data on the occurrence of various injuries. We analyzed the specific patterns of injury by weight category of the Olympic-athlete style and examined the effects of pain on recovery time and the studied the correlation between the type of injury and recovery time.

Methods

Study population

The study was conducted from January 2019 to December 2019 in Korea, with 240 elite adolescent judo athletes who participated in high-level competitions. The research design was approved by the Korea Training Center and the study conformed to the Helsinki Declaration; the Ethics Committee waived the requirement for prior consent. The study population consisted of 120 male (40 lightweight, 40 middleweight and 40 heavyweight) and 120 female (40 lightweight, 40 middleweight and 40 heavyweight) judo athletes. The athletes were classified using Olympic-athlete style weight classes.

Data collection

The training details (weight class and date), athlete characteristics (sex and name), and injury characteristics (body region, site, types, and pain score) were recorded using the daily injury report form issued by the IOC.¹² During the study period, a sports medicine doctor who filled a daily injury form at the site evaluated the athlete before introducing the athlete to the clinic.

Operational definitions

Sports injuries were defined as acute or chronic musculoskeletal signs and symptoms caused by induction activity during training sessions.¹³ Several injuries in one athlete were classified according to the affected body region; several injuries during the same accident were recorded as separate injuries. The location and injury types were classified based on the IOC consensus that analyzed injury propensity.¹²

The affected body regions were defined as follows: head and neck, upper extremities (shoulder, upper arms, elbow, forearm, wrist, and hand), trunk (chest, thoracic, abdomen, and lumbosacral), and lower extremities (hip/groin, thigh, knee, lower leg, ankle, and foot).¹⁴ The injured tissues were defined as follows: muscle/tendon, nervous, bone, cartilage/synovium/bursa, ligament/joint capsule.¹⁴

Recovery time was classified as follows: level I, requiring 1–3 days for recovery; level II, requiring 4–7 days for recovery, and; level III, requiring ≥8 days for recovery.^14–16

The pain score (0 to 10 points’ score) was recorded, and the recovery time was recorded as the duration from the day of the sports injury to the day of normal training and participation.¹⁴ Judo athletes were classified into Olympic-athlete style weight classes as follows: lightweight (60 kg to <73 kg for men, 48 kg to <57 kg for women), middleweight (73 kg to <90 kg for men, 57 kg to <70 kg for women) and heavyweight (≥90 kg for men, ≥70 kg for women).¹⁷

Statistical analysis

The variables analyzed included sex, weight class, injury locations (body site and areas), recovery time, and pain scores; technical statistics were used to investigate injury patterns. Using the χ² tests, we compared, injury locations, and recovery time between groups according to weight class or sex. The injury rate was calculated by the number of injuries per year and the number of injuries per 1000 athlete exposures (AEs); one AE was defined as participation in one training session. The annual abnormal response was calculated, excluding exposures that were not involved in training due to injury; the injury rate calculation per response over 1000 AEs was calculated as follows: Total injury/total AEs of all athletes × 1000. The risk of injury was expressed by the Poisson injury rate and 95% confidence interval (95% CI), and the group with injury rate was compared by the Poisson ratio. In addition, one-way analysis of variance was used to investigate the pain score and recovery time due to sports injury. Simple linear regression analysis was used to investigate the effect of the pain score on recovery time. For all statistical analyzes, SPSS V.26.0 Windows (IBM Corp, Armonk, New York, USA) was used, and the significance level was set as α < 0.05

Results

A total of 240 athletes were included in the study (Table 1); the athletes underwent an average of five training sessions each week. The athletes were at the training center for 10 months (43.5 weeks) over a period of one year.

Table 1.

General characteristics of the subjects.

	Men			Women
	Lightweight	Middleweight	Heavyweight	Lightweight	Middleweight	Heavyweight
N	30	30	30	30	30	30
Athlete exposures	8,006	8,156	8,181	8,139	8,343	8,156
Age (years)	18.82 (2.31)	18.77 (2.24)	18.39 (2.89)	18.13 (2.90)	18.61 (2.22)	18.38 (2.97)
Height (m)	169.73 (3.39)	177.48 (4.21)	181.24 (6.86)	159.58 (5.93)	166.19 (3.55)	172.09 (4.32)
Weight (kg)	69.74 (5.33)	85.11 (6.45)	108.82 (12.49)	53.24 (5.74)	67.45(4.57)	90.11 (11.87)
BMI (kg·m^–2)	23.41 (1.47)	25.11 (1.68)	33.98 (4.95)	21.44 (1.30)	23.94 (1.99)	31.33 (6.63)

Note: Data are presented as mean (±SD).

Injury rates

A total of 617 injuries were recorded during the study period, with no distinction between acute and overuse injuries; the total injury rate per athlete was 2.57 per year.

In terms of exposure, the overall injury rate was 12.60/1000 AEs, and the injury rate was lower in male athletes than in female athletes (15.66 vs. 9.49/1000 AEs; p < 0.001; Table 2).

Table 2.

Injury rates of training for each weight class.

Weight class	Injury rates (95%CI)
Weight class	Men	Women	p Values
Lightweight	10.24 (8.15–12.71)	16.71 (14.02–19.77)	<0.001
Middleweight	9.32 (7.34–11.66)	15.46 (12.91–18.37)	<0.001
Heavyweight	8.92 (6.99–11.22)	14.84 (12.31–17.73)	<0.001
Total	9.49 (8.31–10.80)	15.67 (14.14–17.31)	<0.001

Injury location and type of injury

The location of injuries was most frequent in the following order: lower extremity (39.71%), upper extremity (36.63%), trunk (16.69%), and head and neck (6.97%), and there was a significant difference between the affected areas according to sex (p = 0.023). However, there was no significant difference in the affected areas according to weight class in male and female athletes (p = 0.838, p = 0.116, respectively). The knee, shoulder, lumbosacral, ankle, and hand regions were the most common injury areas among all the judo athletes (Table 3).

Table 3.

Injury location (body region and site) in elite judo Korean athletes.

Site	No (%)
	Men			Women
	Lightweight	Middleweight	Heavyweight	Lightweight	Middleweight	Heavyweight
Head	2 (2.4)	3 (3.9)	3 (4.1)	3 (2.2)	2 (1.6)	1 (0.8)
Neck	4 (409)	3 (3.9)	4 (5.5)	9 (6.6)	6 (4.7)	3 (2.5)
Head and neck	6 (7.3)	6 (7.9)	7 (9.6)	12 (8.8)	8 (6.2)	4 (3.3)
Shoulder	11 (13.4)	14 (18.4)	16 (21.9)	23 (16.9)	21 (16.3)	17 (14.0)
Upper arms	2 (2.4)	1 (1.3)	2 (2.7)	6 (4.4)	5 (3.9)	4 (3.3)
Elbow	2 (2.4)	3 (3.9)	4 (5.5)	8 (5.9)	3 (2.3)	3 (2.5)
Forearm	1 (1.2)	–	2 (2.7)	4 (2.9)	6 (4.7)	2 (1.7)
Wrist	3 (3.7)	5 (6.6)	4 (5.5)	6 (4.4)	6 (4.7)	4 (3.3)
Hand	7 (8.5)	4 (5.3)	3 (4.1)	10 (7.4)	8 (6.2)	6 (5.0)
Upper extremity	26 (31.7)	27 (35.5)	31 (42.5)	57 (41.9)	49 (38.0)	36 (29.8)
Chest	3 (3.7)	1 (1.3)	2 (2.7)	1 (0.7)	2 (1.6)	1 (0.8)
Thoracic Spine	2 (2.4)	3 (3.9)	3 (4.1)	3 (2.2)	4 (3.1)	2 (1.7)
Lumbosacral	13 (15.9)	12 (15.8)	9 (12.3)	9 (6.6)	14 (10.9)	15 (12.4)
Abdomen	1 (1.2)	1 (1.3)	–	1 (0.7)	–	1 (0.8)
Trunk	19 (23.2)	17 (22.4)	14 (19.2)	14 (10.3)	20 (15.5)	19 (15.7)
Hip/groin	1 (1.2)	–	1 (1.4)	2 (1.5)	1 (0.8)	2 (1.7)
Thigh	3 (3.7)	5 (6.6)	3 (4.1)	8 (5.9)	6 (4.7)	8 (6.6)
Knee	15 (18.3)	11 (14.5)	8 (11.0)	22 (16.2)	27 (20.9)	31 (25.6)
Lower Leg	3 (3.7)	2 (2.6)	4 (5.5)	6 (4.4)	4 (3.1)	4 (3.3)
Ankle	7 (8.5)	5 (6.6)	3 (4.1)	9 (6.6)	9 (7.0)	12 (9.9)
Foot	2 (2.4)	3 (3.9)	2 (2.7)	6 (4.4)	5 (3.9)	5 (4.1)
Lower extremity	31 (37.8)	26 (34.2)	21 (28.8)	53 (39.0)	52 (40.3)	62 (51.2)
Total	82 (100.0)	76 (100.0)	73 (100.0)	136 (100.0)	129 (100.0)	121 (100.0)

Note: Data provided as absolute incidence and frequency of injury at a specific site or in a specific body region, relative to the total number of injuries noted over the entire observation period.

The most common types of injury were muscle (35.66%), ligament (26.26%), cartilage (21.88%), tendon (10.86%), and bone (5.35%) injuries (Table 4).

Table 4.

Injury type in elite judo Korean athletes.

Tissue	Pathology type	No (%)
Tissue	Pathology type	Male	Female	Total
Muscle	Strain	75 (32.47)	104 (26.94)	220 (35.66)
	Muscle tear	7 (3.03)	6 (1.55)
	Muscle rupture	3 (1.30)	2 (0.52)
	Muscle contusion	9 (3.90)	14 (3.63)
Tendon	Tendinosis	19 (8.23)	38 (9.84)	67 (10.86)
Tendon	Tendon rupture	3 (1.30)	7 (1.81)	67 (10.86)
Bone	Bone stress injury	2 (0.87)	6 (1.55)	33 (5.35)
Bone	Bone contusion	8 (3.46)	17 (4.40)	33 (5.35)
Cartilage/Synovium/Bursa	Cartilage injury	9 (3.90)	26 (6.74)	135 (21.88)
	Arthritis	14 (6.06)	29 (7.51)
	Synovitis/capsulitis	9 (3.90)	18 (4.66)
	Bursitis	7 (3.03)	23 (5.96)
Ligament/Joint capsule	Joint sprain (ligament tear or acute instability episode)	66 (28.57)	96 (24.87)	162 (26.26)

Recovery time

Among all judo athletes, 56.08% of injuries were classified as level I, 20.26% as level II, and 23.66% as level III. The recovery time was significantly different according to sex (p = 0.042). Weight class had significant effects on recovery time in both men and women (p = 0.032 and p = 0.023, respectively). In addition, the recovery time varied according to the affected body parts of male and female athletes (Table 5). Level 3 injury was mostly ligament, and the average recovery time was 12.81 day.

Table 5.

Statistical results of injuries in elite Judo Korean athletes.

Injury	No (%)
Injury	Level I	Level II	Level III	df	x²	p Values
Men	115 (49.8)	56 (24.2)	60 (26.0)	2	6.304	0.042
Women	231 (59.8)	69 (17.9)	86 (22.3)	2	6.304	0.042
Men				2	10.563	0.032
Lightweight	30 (36.6)	28 (34.1)	24 (29.3)
Middleweight	42 (55.3)	16 (21.1)	18 (23.7)
Heavyweight	43 (58.9)	12 (16.4)	18 (24.7)
Women				2	11.383	0.023
Lightweight	85 (62.5)	18 (13.2)	33 (24.3)
Middleweight	74 (57.4)	34 (26.4)	21 (16.3)
Heavyweight	72 (59.5)	17 (14.0)	32 (26.4)
Head and neck	30 (69.8)	9 (20.9)	4 (9.3)	6	29.485	<0.001
Upper extremity	117 (51.8)	59 (26.1)	50 (22.1)
Trunk	71 (68.9)	19 (18.4)	13 (12.6)
Lower extremity	128 (52.2)	38 (15.5)	79 (32.2)
Men				6	14.345	0.026
Head and neck	13 (68.4)	5 (26.3)	1 (5.3)
Upper extremity	45 (53.6)	20 (23.8)	19 (22.6)
Trunk	29 (58.0)	11 (22.0)	10 (20.0)
Lower extremity	28 (35.9)	20 (25.6)	30 (38.5)
Women				6	29.411	<0.001
Head and neck	17 (70.8)	4 (16.7)	3 (12.5)
Upper extremity	72 (50.7)	39 (27.5)	31 (21.8)
Trunk	42 (79.2)	8 (15.1)	3 (5.7)
Lower extremity	100 (59.9)	18 (10.8)	49 (29.3)

Pain score and recovery time according to injury types

The type of injury influenced the pain score (p < 0.001). The pain score of ligament injury was the highest, followed by that of muscle, bone, tendon, and cartilage injuries (Table 6). In addition, the type of injury influenced recovery time (p < 0.001). Athletes with ligament injury had the longest recovery period, followed by those with tendon, bone, cartilage, and muscle injuries (Table 6).

Table 6.

Difference in the pain score and recovery time between type of injury.

Injury type	No (SD)
Injury type	Muscle	Tendon	Bone	Cartilage	Ligament	F	p Values
Pain score	5.35 (1.36)	4.94 (1.70)	5.27 (1.57)	4.57 (1.47)	6.56 (1.13)	42.236	<0.001
Recovery time	4.21 (1.83)	8.24 (6.01)	7.27 (3.79)	5.78 (3.37)	12.08 (3.71)	129.207	<0.001

Relationship between pain score and recovery time

The association between pain score and recovery time was statistically significant (p < 0.001). When the pain score decreased by 1 in the athletes, the recovery time was decreased by about 1.47 days.

Discussion

We attempted to discern the sports injury patterns of elite adolescent Korean judo athletes by evaluating the association between injury rate and location based on sex and weight class. We also aimed to investigate the effects of pain on recovery time according to the type of injury.

Injury rates

Three prospective studies examined the sports injuries during the 2016 Rio Olympic Games,³ the 2012 London Olympic Games,⁴ and the 2008 Beijing Olympic Games.⁵ Data from these three studies were only discussed in relation to the incidence rates, proportions, and characteristics as well as common diagnoses of sports injuries. More than 10% of judo who participated in the 2016 Rio Olympics,³ 2012 London Olympics,⁴ and the 2008 Beijing Olympics⁵ experienced sports injuries. Although this was less than the proportion noted in football, Taekwondo, the rate of injury has increased in judo every successive Olympics games.^3–5 This is because elite athletes are more involved in high-risk activities as their desire to win matches outweighs health concerns.¹⁵ Other reasons for such an observation might include variations in the level of coaching supervision and differing levels of healthcare.¹⁸ The causes of injury can differ between different sports. However, football, Taekwondo, and judo have at least one thing in common – more than 50% of injuries are caused by contact with other athletes.⁵

Injury location and type of injury

In the current study, injuries were most common in the lower limbs, followed by the upper extremities, trunk, head, and neck. Three previous studies reported injury data for competitions associated with induction events.^9–11 Previous studies that included judo athletes only distinguished injury rates and did not consider weight class or recovery time. Although differences in study design preclude a direct comparison between our results and those of previous studies, most injuries occurred in the upper extremities based on the findings of studies among judo athletes from USA National Championships,⁹ French Judo Federation,¹⁰ and Brazilian National Championships,¹² and the second most commonly affected body parts varied between studies. Another interesting difference is that head and neck injuries were commonly reported in other studies, but few were observed in this study (6.97%). The difference in outcomes for Korean and foreign athletes may be related to differences in combat style, body structure, and training methods. Korean athletes frequently use the foot techniques (ashi-waza),¹⁹ while foreign athletes use the hand techniques (te-waza).²⁰ As a result, there is higher incidence of lower extremity injuries among Korean athletes. In addition, the most common injuries in this study was to the muscle, followed by ligament, cartilage, tendon, and bone; this was similar to findings in previous studies.¹¹

Weight class differences in terms of injury patterns

Previous studies have reported that most induced injuries are not serious;^9–11 however, specific definitions of recovery time categories were not provided in these studies. In our study, weight class had a significant effect on the recovery time in both men and women; and the distribution and recovery time in different parts of the body differed significantly in terms of weight class. However, we cannot compare our results with previous observations because they did not provide information about the severity of injury by weight classes, as mentioned.

Sex-specific differences in terms of injury patterns

Kim and Kim²¹ reported that the incidence of sports injury differed between male and female. We also noted that female displayed a higher injury rate than male. If there is impairment within the neuromuscular component during movement, the pattern of movement can may change; thus, increasing the risk of injury, with more frequent injuries probably occurring in females than in males being attributable to due to a lack of neuromuscular control.²² Scott et al.²³ reported that amplitude and timing differences in neuromuscular activity have differed between sex during the pre-contact and early stance phases of two unanticipated cutting maneuvers. The differences suggest that the activation patterns observed in females might not be providing adequate joint protection and stability. In addition, the most common injury related to differences in neuromuscular control is injury to the ligament. Women are at higher risk for ligament injury than men.²⁴

Recovery time

In the current study, there was significant difference among male and female athletes in terms of recovery time. Overall, we found more level I injuries in female athletes, while male athletes exhibited more level II and level III injuries. The main reasons for this difference include the manner in which glucose is utilized and the type of skeletal muscle fiber. Women have a high amount of type-I fiber and increased capillary vascular density, which can improve tissue perfusion and elevate glucose and fatty acid oxidation ability, preventing fatigue.²⁵ The other reason is that men have high testosterone levels, while women have high estrogen levels. Mitochondrial estrogen receptors increase glucose uptake to muscles when activated. Women tend to convert fat to energy more efficiently and feel less fatigue.²⁶

Pain score and recovery time according to injury types

The pain score was highest in the case of injuries to the ligament, followed by those to the muscle, bone, tendon, and cartilage. However, since the self-administered pain score is subjective and based on evaluation by the participants, it is difficult to assess serious injury and associate it with the pain score. Edwards and Fillingim²⁷ reported that the sensitivity of pain measured by the Thermal Sensing Analyzer is not related to the sensitivity of self-awareness pain. In our study, recovery time according to the type of injury was highest in the case of ligament injury, followed by tendon, bone, cartilage and muscle injuries. The pain score associated with muscle injury was the second-highest, but the recovery time because of muscle injury was the shortest.

Ligaments, tendons, and cartilage have fewer blood vessels compared to muscles; thus, they have poor regeneration capacity,²⁸ and it is therefore natural that the recovery time associated with muscle injury is longer. Nevertheless, the reason for the high pain score of muscle injury is unclear. One reason could be the fear of recurrence. Rosenbloom et al.²⁹ reported that the pain score was but by psychological factors and stress.

In general, judo athletes are known to have a high incidence of recurrent injury⁸ and, in our study, they had a notable rate of muscle and ligament injuries. Therefore, these athletes would have largely accepted the degree of pain due to psychological factors and previous experience with such injuries. In addition, most athletes wish to resume as soon as their physical capacity allows it and ignore sequellae pain if it does not hinder them in their practice/this may also explain the fact that there are recurrences or injuries that become chronic.³⁰ In our study, when the pain score decreased by 1, the recovery time decreased by about 1.47 days. This result is presumed to have been due to the high pain score and prolonged average time periods required to recover from a ligament injury. Further research is needed for clarification.

Strengths and limitations

In the current study, a large number of athletes were observed closely for 10 months (43.5 weeks), totalling 48,981 AE per year. Moreover, a detailed analysis of the recovery time, incidence and location of the injuries was performed with an extremely high inclusion rate. All injuries that occurred at the training facility was reported and handled within the on-site facilities, and this made for consistent data gathering. Our study considered the influence of weight class category. An additional strength of the study was that the number of injuries was analysed by subcategories to address novel research questions that are relevant to the judo sports medicine community. However, we did not have any information regarding biomechanical injury mechanisms.

Conclusions

The findings of this study may assist in developing methods to prevent injuries among elite judo athletes who are expected to represent South Korea in future games. In future, video may be used to analyze trauma, both during matches and during training, in order to determine the common mechanisms of injury.

Footnotes

Authors' note

Hyun-Chul Kim is now affiliated with Department of Physical Therapy, Yongin University, South Korea.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Ki-Jun Park

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