Pediatric Exercise Science, 1997,9, 55-64 O 1997 Human Kinetics Publishers, Inc.

The Effect of Karate Training on Flexibility, Muscle Strength, and Balance in

8- to 13-Year-Old Boys

Mariona A. Violan, Eric W. Small, Merrilee N. Zetaruk, and Lyle J. Micheli

The effect of 6 months of twice weekly karate training on flexibility, balance, and strength was evaluated in 14 boys who perform karate as beginners (age M = 10.3 f 1.8) and a group of the same age who had never been involved in martial arts (n = 10; age M = 10.9 + 1.4). All subjects were pretested and posttested on the following: flexibility of upper extremity (shoulder), ham- strings and quadriceps; strength, including handgrip strength and concentric flexionlextension of quadriceps; and balance, with eyes either open or closed. After 6 months, the tests were evaluated and compared by groups. The results showed the karate group made significant gains on quadriceps flexibility and balance with eyes closed. By improving flexibility, balance, and strength, ka- rate improves three of the basic fitness components that are very important for preventing sport injuries in the growing years.

Approximately 1.5 to 2 million Americans are involved in martial arts, about 20% of whom are children (14,21). Karate is becoming increasingly popular among . children in the United States. The activity gives participants a sense of physical and mental fulfillment and develops qualities such as respect, discipline, concen- tration, patience, and self-confidence in the young karateka. In addition, training in martial arts has been show to decrease hostility (16).

Few published studies have evaluated the physiological characteristics in martial arts. It has been shown that strength and flexibility increase in adult or elite martial arts athletes (4). To date, there are no reports comparing the effect of karate training on flexibility, balance, and strength in beginners, especially children.

It is well known that flexibility, strength, and balance are three of the basic fitness components (10,23), and improving strength and flexibility may help pre- vent sports injuries (5, 18,20). The purpose of this study is to evaluate the effect of 6 months of karate training on strength, flexibility, and static balance in 8- to 13- year old boys with no previous martial arts experience and compared with a group of boys involved in recreational sports.

Mariona A. Violan, Eric W. Small, Merrilee N. Zetaruk, and Lyle J. Micheli are with the Division of Sports Medicine, Children's Hospital, 300 Longwood Avenue, Boston, MA 02115.

56 - Violan, Small, Zetaruk, and Micheli

Methods

Subjects

Subjects were selected from a beginner's class at a Boston area private karate school (Uechi-Ryu style). The control group consisted of boys who had never been involved in martial arts but who participated in recreational sports. The boys and their parents were informed about the purpose of this study, and written consent was obtained from the parents or legal guardians. Eighteen boys from a karate school were self-selected. The 14 boys who finished the study participated in karate class twice a week for 60- 70 rnin each session (age range = 8-13, M = 10.2 + 2.0 ). Ten other boys, ages 8-12 (M = 10.9 + 1.4) were asked to volunteer in this study. These boys had never done martial arts before, and were primarily involved in recreational sports such baseball, football, and basketball up to 3 days a week (60-90 minutes each session). Both groups participated in physical education classes.

The karate group had the same instructor for 6 months, and the sessions fol- lowed the same methodology according to Uechi-Ryu style. The class has five parts:

1. Warm-up using Uechi-Ryu technique, initialized from feet and ending on neck (footlankle rotation and stretching, kneelleg stretching with leg lift and kicking, waistltrunk stretching and rotations, shoulderlarm double crossing and stretching, and finally neck stretching). (10-13 min)

2. Exercises of blocking with both arms, specifically Uechi-Ryu arm move- ments. (2-4 min)

3. Study and practice of katas in three times: (a) slow dynamic tension, (b) relax and speed, and (c) entire body at the same time. (15 rnin)

4. Technique exercise, comprising 13 exercises of blocking and striking, al- ways beginning with blocking. After this exercise is kata performance. Three to four katas are taught for the first 6 months. These were practiced several times for improvement and memorization. (20 min)

5. Applications and body toughening exercises, stretching exercises, self-control, and bowing. (10 min)

All subjects were tested on two occasions: at the start of karate training, and at 6 month into karate season. At the same time, the control group was also tested. Baseline characteristics were also tested of the two groups and they are shown in Table 1.

Table 1 Baseline Characteristics

Karate group (n = 14) , Control group (n = 10)

Age 10.2 f 2.0 Height (cm) 136 f 9.4 Weight (kg) 30.9 + 6.4 Sum of skinfolds (mm) 13.6 + 5.5

Note. Values are M + SD.

Effect of Karate Training - 57

Anthropometric Measurements

Weight was measured in kilograms by a scale with subjects wearing shorts and no shoes. Height was recorded in centimeters, without shoes and in maximal inspira- tion. For sum of skinfolds, two skinfolds were measured using a Lange skinfold caliper; sites tested were triceps and subscapular (2). Each site was measured three consecutive times. The sum of skinfolds and the mean of three scores was re- corded. Many parameters were tested by an experienced group of physicians and physical therapists, and they will be discussed in turn.

Flexibility. Static flexibility (passive flexibility that refers to the range of motion of joints) was measured, with the best of three attempts was used for analy- sis. The following areas were tested:

Upper Extremities: The test for shoulder flexibility consisted of raising the right elbow and reaching the right hand down between the shoulder blades while the left hand was placed in the small of the back with the palm facing outward. The distance between the fingertips was measured in centimeters and was recorded as "overlap." Positive numbers indicate overlap and nega- tive numbers denote no overlap (1, 5, 17). Hamstring: Hamstring flexibility was tested with the subject in a supine position, both the hip and the knee at 90". The examiner then extended the knee slowly until muscle resistance was felt, taking care to avoid a change of hip position and keeping the lower back flat. The degree of extension from the starting position was measured (1,5, 8). Quadriceps: The Ely test (1) was used. The examiner slowly flexed the knee of the prone subject until muscle resistance was felt. In this test, the hip should not flex; if the subject has tight quadriceps, the heel will not reach the buttocks, or will do so only if the pelvis (on the same side) rises up off the table (8).

Static Balance. Static balance refers to the ability of the subject to main- tain bodily equilibrium with eyes either open or closed. To evaluate this, the Fla- mingo test was performed (10). The subjects stood with their preferred foot lengthwise on a wooden rail (1.5 in. high, .75 in. wide, 24 in. long). The subjects maintained balance with their hands on their hips. The length of the time was recorded in seconds and ended when any part of the body touched the floor or when either hand was removed from the hips. The same test was repeated with eyes closed. The best of three trials was recorded.

Handgrip Strength. Right handgrip strength was measured three times with a grip dynamometer (JAMAR), which measures strength (kilograms force) isometrically by compression of a spring. The procedure was as follows: The sub- ject stood in an erect position, with arm at a side and elbow flexed at 90°, held the grip dynamometer comfortably in one hand. The subject then gripped the dyna- mometer as hard as possible. The best of three trials was recorded.

Leg Muscle Strength. The assessment of right knee extensor and flexor muscle strength at a 60'1s was done using isokinetic testing with a Kin-Corn dyna- mometer. Each subject's maximal concentric quadriceps femoris muscle strength during an isokinetic movement at 60'1s. was tested. The subject's back was sup- ported by the backrest, and the right knee was placed next to the lever arm. Straps

58 - Violan, Small, Zetaruk, and Micheli

were placed across the pelvis and the distal thigh. Measurements were done in newtons. We tested the concentric peak extension (CPE) and the concentric peak flexion (CPF) three times each on the right leg (13, 14, 15). The best of three attempts was recorded.

All values of muscle strength were expressed in absolute terms or as weight- adjusted strength: strength divided by body weight multiplied by 100 to yield muscle strength in terms of percent body weight.

Statistical Analysis

Data are expressed as mean + standard deviation (M f SD). The differences be- tween groups and time interactions were analyzed by analysis of covariance for repeated measures, with pretest data corrected for initial differences between groups. Data analysis and calculations were performed with SuperANOVA statis- tical package (Abacus Concepts, Berkeley, CA). A p < .05 was considered signifi- cant.

Results

Fourteen of the 18 boys completed the study. Only one subject dropped out of the karate program, and the other 3 subjects failed to show up for follow-up testing. All subjects from the control group were pre- and posttested. Only one dropped out of his sport activities at 2 months, but not for medical reasons. When baseline characteristics of both groups (Table 1) were compared, the karate group had lower body weight, shorter stature, and a lower sum of skinfolds. However, we believe that it is unlikely that the differences in anthropometric parameters between groups at the beginning of the study could have influenced the outcome in flexibility and equilibrium observed after the training period.

After 6 months of karate training, the karate group showed gains in all pa- rameters tested, the most significant increases being in quadriceps flexibility, ham- string flexibility, balance (eyes closed), quadriceps strength (CPE), and handgrip strength. The control group showed improvement in scores, excluding balance and CPEICPF, which decreased.

A comparison of the quadriceps flexibility before training reveals a similar range of motion for both the karate and the control group (130.4 + 8.0 and 128.7 k1.3, respectively). After 6 months, quadriceps flexibility increased in both groups; however, only the karate group improvement was high. When we compared the improvement of quadriceps flexibility in the karate group with that of the control group, we found that the greater increase in karate was statistically significant O) < .03). At the beginning of the study, hamstring flexibility was greater in the control group than in the karate group. On follow-up testing, the hamstring flexibility was similar between the two groups. The amount of change in the karate group com- pared with the control group was not statistically significant. Shoulder flexibility testing showed no significant changes in either group (see Table 2).

The control group was stronger before the study, but after 6 months, no sta- tistical differences were noted when compared to karate group, suggesting a de- crease on CPE and CPF for the control group. The difference between these changes did not reach statistical significance when compared over time between groups (see Table 3).

Table 2 Changes in Flexibility

Karate (n = 14) Control (n = 10)

Pretest Posttest Change Pretest Posttest Change pa

Quadriceps flexibility (degrees) 130.4 f 8.0 143.1 k 7.1 12.7 k 10.7 128.7 k 1.3 135.8 f 6.4 7.1 k 10.4 .03 Hamstring flexibility (degrees) 29k13.3 40.2k9.2 11.1k11.2 39.7 k 11.1 42.6 f 7.4 2.9 f 11.3 ns Shoulder flexibility (cm) 3.9 k 4.6 4.7 k 5.4 0.8 k 4.2 -1.2 k 4.8 0.2 f 5.3 1.4 f 4.1 ns

Note. Values are M f SD. "p values refer to the comparison between karate and control group.

Table 3 Changes in Strength

Karate (n = 14) Control (n = 10) rn f:

Pretest Posttest Change Pretest Posttest Change pa 0 S

- - Handgrip strength (kg) 19.3 k 3.8 20.6 + 4 1.3 + 1.5 25.5 f 6.1 26 k 6.4 0.5 k 0.9 ns $ Concentric peak extension (Nw) 191.8 f 99 214 k 89.2 22.6 k 35.7 278 k 18 264.3 k 118.2 -14.2 1t 84.1 ns Concentric peak flexion (Nw) 94.6-t-41.2 106k 37.4 11.3 k 19.5 150f 50.1 145.6f48.2 -4.3 k 18 ns 2 -

Z. 3 0

Note. Values are M + SD. I VI

"p values refer to the comparison between karate and control group. (D

60 - Violan, Small, Zetanrk, and Micheli

Balance showed a decrease in scores in the control group, this decrease was seen with eyes open, as well as with eyes closed. In contrast, boys in the karate group improved their balance. When results were compared by groups, balance with eyes closed was statistically significant ( p = .007) (see Table 4). Balance with eyes closed or open was superior in the karate group, even before the training, and the gains in this group were much greater in balance with eyes open.

Discussion

Strength, flexibility, and balance are three of the basic fitness, components (10,23). Other important components are speed, coordination, cardiovascular endurance, mus- cular endurance, and body composition (5). This study demonstrates results that boys participating in karate trainingmade improvements in flexibility, especially quadri- ceps, as well as balance (eyes closed) when compared to an age-matched control group. The karate group showed an increase in all strength tests, whereas the control group actually showed a decrease. However this change did not demonstrate statisti- cal significance when compared over time between groups. .

Flexibility is an important factor in human athletic performance and in injury prevention (7,16). It is one of the five specific components of health-related physical fitness. It is well known that some sports such as figure skating, gymnastics, ballet, and diving require good flexibility for proficient performance. Flexibility exercises have become an integral part of preseason and in-season training. Furthermore, the necessary type and location of flexibility varies for different sports. The value of flex- ibility for optimal athletic performance and prevention of injuries is well recognized (5). It is particularly important during times of maximal growth. Flexibility tends to decrease to minimal levels between the ages of 10 and 12 (5, 15, 22), which is the period of maximal linear growth, and then improves again toward early adulthood (24). Bones grow more quickly than muscles and tendons, which results in decreased flexibility. ~ e v e l o ~ i n ~ tissues such as bone, articular cartilage, and tendon-bone junc- tions are more susceptible to injury (15). The aforementioned reasons emphasize the importance of flexibility training during the growth spurt.

The boys who were involved in karate training twice a week for 60 min per session, which included approximate 10 min of stretching exercises before and after class, did not show evidence of a relative decrease in flexibility during the period of maximal linear growth. In the general population, a decrease in flexibility usually occurs at this stage of development. As mentioned in the Results section, there was a highly significant difference in improvement of quadriceps flexibility when the karate and control groups were compared.

Karate training includes both static and dynamic stretching when participants are learning skills. Short muscles increase the risk of sports injuries to muscle-ten- dons, bones, and physes, especially during the prepubescent period; a joint with less than full range of motion is equally vulnerable (5, 15, 19). We did not find flexibility imbalances that are a cause of overuse injuries (18,20) in this age group.

One,of the variables believed to be very important for developing fundamental motor skill is balance, either static (stationary body) or dynamic (while moving). In general, there is no significant improvement in static balance among 8- to 12-year-old boys who have not received specific training in this area. (3). Furthermore, some research indicates that balance control may actually decrease between 10 and 12 years of age. (13). Opportunities to participate in sports such as baseball or softball may improve the development of specific skills like balance.

62 - Violan, Small, Zetaruk, and Micheli

The karate group showed a greater improvement in balance with eyes closed than with eyes open than did the control group. One explanation is that karate training indirectly improves body equilibrium through specific movements and correct body alignment. For example, proper alignment of the feet, knees, hips, and spine aids in balance during techniques such as kicking and blocking. Without the aid of visual input, proprioception becomes relatively more important for bal- ance. Our study suggests that karate training results in greater improvement in proprioception than in visual input as components of balance.

Strength in lower and upper extremities rises steadily starting from ages 8- 12 years, with further rapid increases in boys occumng even after longitudinal and ponderal growth has ceased (11, 25). It is known that muscle strength increases parallel to growth at this age (9, 12). Recent studies have shown that children are able to increase strength by resistance training, but are less likely to increase muscle - .

bulk in a strength-training program. There i s clear evidence-of improvement in strength with resistance training; however, muscle hypertrophy and increased body mass seldom occurs beyond that associated with normal growth (12). One hypoth- esis to explain this observation is that strength depends not only on an increase in muscle mass, but also on a qualitative developmental process (24).

Muscle strength in the lower extremities increased in the karate group; how- ever, one would have expected a greater increase in strength in the control group given its higher rate of linear growth. Trends of improvement in PCE and CPF occur among karate group. Because there was no increase within the control group, it is likely that karate training may results in increase in lower extremity strength.

Handgrip strength increased in both groups; however, when the increase in each group was compared, there was no statistical significance between the karate group and the controls. One possible explanation is that the recreational activities the control group was involved in (e.g., baseball, football) helped develop handgrip strength to the same extent that the Uechi-Ryu karate techniques developed those of the karate group. The Uechi-Ryu karate style uses open-hand tech- niques. Other karate styles that concentrate on closed-fist techniques (e.g., Shotokan) may result in greater increases in handgrip strength.

The increases in flexibility and balance were more significant in the karate group than in the control group, but it is important to note that fewer hours of training were done by children in the karate group. This means that the specific improvements are not due solely to the number of hours of training, but are a response to sport-specific skills.

In conclusion, the nature of karate training selectively improves flexibility of the quadriceps and static balance, especially eyes closed in 8- to 13-year-old boys. These results show that karate training twice a week may improve static flexibility and balance. Karate can be an effective method for improving range of motion, bal- ance, and conditioning in boys of this age group. Research has shown that good muscle balance in terms of strength and flexibility decreases the risk of overuse injuries. By improving the range of motion and strength, karate training may help prevent sports injuries, but further research needs to be done to confirm this hypothesis.

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