INTRODUCTION
The objective of training for athletes is to improve factors such as body composition correct for their sport, physical fitness, technical, and psychological skills, and to optimize athletic performance (Bridge et al., 2014; Buchheit et al., 2013). Pre-season training improves the physical performance of athlete’s depleted performance. Fitness evaluation can predict performance during the season and contribute to attainment of program goals (Argus et al. 2010).
Among factors that evaluate the performance of elite athletes, fat tissue and lean tissue are important indicators that verify the effect of training, in light of differences in type of sport, gender, and performance levels, and reportedly influence the early selection of elite athletes and their performance (Desiere et al., 2004; Mudd et al., 2007). In the case of taekwondo, in particular, it is reported that elite athletes have higher lean mass and lower fat mass than non-elite athletes (Bridge et al., 2014; Fritzsche and Raschka, 2007; Markovic et al., 2005). In relation to physical fitness, factors such as agility, strength, endurance and flexibility are considered very important in taekwondo competition (Bridge et al., 2014; Casolino et al., 2012; Markovic et al., 2005). Since more than 90% of scoring is based on kicking skills, in particular, muscle power and endurance in the lower extremities are required (Casolino et al., 2012; Matsushigue et al., 2009; Santos et al., 2011; Tornello et al., 2013). In addition, during a two-minute, three-round taekwondo match, mean heart rates (Mean HR) of athletes can reach 85% of maximum (HR max), validating it as a high-intensity sport (Bridge et al., 2013; Chiodo et al., 2011; Matsushigue et al., 2009); thus, performance relies heavily on anaerobic metabolism, since scoring is achieved through attacks within very brief time intervals, e.g. 3–5 sec (Fong et al., 2011; Marcovic et al., 2008). Therefore, athletes must be trained to improve their anaerobic capacity. As noted above, factors such as body composition, physical fitness, anaerobic capacity, and isokinetic muscle strength affect an athlete’s performance in taekwondo.
Approximately 20–60% of athletes in sports have experienced overtraining (Purvis et al., 2010), which may lead to injuries to the nerves, and the musculoskeletal and cardiovascular systems (Cosca and Navazio, 2007; Margonis et al., 2007), as well as a decline in performance. Pre-season training of taekwondo athletes, in particular, is mostly based on the experience of the coaching staff or the athletes themselves, but there is no study closely examining the factors that affect performance in competition in Korea.
This study carefully analyzed the effect of 8 weeks of pre-season training on changes in body composition, physical fitness, anaerobic capacity, and isokinetic muscle strength, with the purpose of presenting study material that can maximize the efficiency of sports training programs.
MATERIALS AND METHODS
Subjects
The randomly selected subjects were 34 male and female athletes 18–21 yr old, who attended K University in Y City. None of the subjects had physical or weight loss problems, or were taking any medication. They were informed of the test procedures before providing written consent. The characteristics of the research subjects are shown in Table 1.
Variables
Body composition
The effects of the taekwondo training program on body composition were determined. Estimates of percent body fat were calculated based on measurements of fat and lean tissue and bone mineral density via dual X-ray absorptiometry (DXA, Hologic QDR-4500, USA). The coefficient of variance of scanning was 1.5%, which is in agreement with that indicated by the manufacturer.
Physical fitness
The Eurofit physical fitness test (1988) was used, and 9 variables for 4 factors were tested. Each test was performed according to the following sequence: flexibility (sit and reach), power (standing long jump), agility (50 m shuttle run), and cardiorespiratory endurance (20 m multistage endurance run).
Wingate anaerobic power test
The Wingate anaerobic power test (WAPT) was performed on a cycle ergometer (Monark 707, Sweden). Before beginning the test the seat was adjusted to the participant’s height. This was followed by a 2–3-min warm-up. The 30-sec test used a load of 0.075 kp per kg the subject’s body weight. The number of revolutions pedaled during every 5-sec interval was recorded. Variables measured included relative peak power, anaerobic capacity, and fatigue index.
Isokinetic strength
Isokinetic dynamometry (Cybex, 770 NORM, USA) was performed to evaluate flexion and extension of the right and left knees. Each test included 3 maximal contractions at 60°/sec for muscle strength, and 20 maximal contractions at 180°/sec for muscle endurance. Each isokinetic contraction was performed through a full range of motion, and data were normalized to each participant’s body weight, and calculated as torque and total work done ([Nm]÷[kg]) ×100.
Training program and training Intensity
As shown in Table 2, the training program included high-intensity continuous running and stair climbing in the morning, low-intensity continuous running and circuit training in the afternoon, and a program of sit-ups and push-ups in the evening. High-intensity continuous running was conducted at 85–90% of HRmax, and long, slow distance running at 60–80% of HRmax. Circuit training and was conducted at 40–60% intensity, of 20 repetitions each section. The sit-up and push-up program consisted of 3 sets of 40 repetitions. To monitor the work intensity during each training session, a heart rate monitor (Polar, RS 400, USA) was used. The average heart rate for each session was divided by 100 to calculate an index of mean exercise intensity.
Statistical analysis
Statistical analysis was performed using the SAS version 9.2 (SAS Institute, NC, USA) software for Windows. All data were presented as mean and standard deviation values. A paired t-test was used to analyze changes over time for each parameter. A P<0.05 was considered as statistically significant.
RESULTS
Body composition
Changes in body composition of collegiate taekwondo athletes after 8 weeks of pre-season training are presented in Table 3. As a result of training, there was a statistically significant reduction in weight (P<0.05, P<0.01, respectively) for both males and females. Percent body fat of males decreased from 11.4±2.28% before to 9.9±1.50% after training (P<0.0001), and fat tissue reduced from 8.1±2.30 kg to 6.8±1.52 kg (P<0.0001). Percent body fat of females reduced from 23.2±3.58% before to 21.2±3.09% after training (P<0.001), and fat tissue also significantly reduced from 14.0±3.0 kg to 12.4±2.48 kg (P<0.001). There was no statistically significant difference in lean tissue for either males or females. Bone mineral content increased significantly in males, from 3,031.1 ±404.41 g before to 3,049.8±403.53 g after training (P<0.001), and bone density increased from 1.29±0.09 g/cm2 before to 1.31±0.10 g/cm2 after training (P<0.05).
Physical fitness
Changes in physical fitness are presented in Table 4. The effect of training on flexibility (sit and reach) and power (standing long jump) was not significant for either males or females. Agility (50 m shuttle run) significantly positive effect for males, from 17.0±0.92 sec before to 16.2±0.99 sec after training (P<0.0001); there was also an improvement for females, from 19.1±0.92 sec before to 18.4±0.70 sec after training (P<0.01). The 20 m multi-stage endurance run improved significantly for males, from 107.7±9.56 times before to 117.9±8.91 stages after training (P<0.0001); there was also a positive training effect for females, from 77.6±11.21 times to 87.4±11.37 times (P<0.0001).
Wingate anaerobic power test
Changes in anaerobic capacity of collegiate taekwondo athletes after 8 weeks of pre-season training are presented in Table 5. Relative peak power per body weight for males significantly improved from 10.2±1.31 W/kg before to 10.9±0.88 W/kg after training (P<0.05). Mean power for males also improved significantly from 7.5±0.67 W/kg before to 8.3±0.59 W/kg after training (P<0.0001).
Isokinetic strength
Maximum muscular strength
Changes in isokinetic maximum muscular strength of male and female collegiate taekwondo athletes after 8 weeks of a pre-season training program are presented in Table 6. Left extensor angular velocity at 60°/sec significantly increased for males, from 271.9±37.12% body weight (BW) before to 315.1±39.09% BW after training (P<0.0001); there was also a significant increase for females, from 222.9±16.97% BW to 281.3±30.79% BW (P<0.0001). Right extensor angular velocity at 60°/sec significantly increased for males, from 274.3±39.83% BW before to 327.5±40.14% BW after training (P<0.001); there was also a significant increase for females, from 223.7±14.29% BW before to 278.5±30.69% BW after training (P<0.05). Right flexor angular velocity at 60°/sec significantly increased for males, from 182.5±24.32% BW to 196.0±21.35% BW (P<0.05), but there was no significant change for females.
Muscle endurance
Changes in isokinetic muscle endurance of male and female collegiate taekwondo athletes after an 8-week pre-season training program are presented in Table 7. Left extensor angular velocity at 180°/sec significantly increased for males, from 3,676.0±445.28% BW before to 4,651.4±417.39% BW after training (P<0.0001); there was also a significant increase for females, from 2,891.2±324.94% BW to 3,736.7±311.74% BW (P<0.0001). Right extensor angular velocity at 180°/sec significantly increased for males, from 3,660.7±521.67% BW before to 4,696.1±416.01% BW after training (P<0.0001); there was also a significant increase for females, from 2,926.9±415.65% BW to 3,576.5±365.05% BW (P<0.01). Left flexor angular velocity at 180°/sec significantly decreased for males, from 3,473.0±420.16% BW before to 3,209.1±431.1% BW after training (P<0.05); there was also a significant decrease for females, from 2,647.0±389.91% BW to 2,287.0±475.91% BW (P<0.05).
DISCUSSION
Body composition
Body composition plays an important role in determining an elite athlete and is closely related to performance (Stanforth et al., 2014; Zemski et al., 2015). The level of body fat, together with anaerobic and aerobic capacity, not only influences physical fitness factors, such as agility and power, but is also related to menstrual irregularity and amenorrhea in female athletes (Casajus, 2001; Duthie et al., 2003; Pitts et al., 2014; Sedeaud et al., 2012).
In the present study, 8 weeks of pre-season training for collegiate male and female taekwondo athletes significantly decreased percentage body fat and fat tissue. However, despite a positive pre-season training effect, with significant reduction in percent body fat, female athletes in this study still had a higher percentage than the national women’s teams of Croatia (14.8±1.7%), Germany (15.8±2.5%) and Italy (16.5±4.9%) (Chiodo et al., 2011; Fritzsche and Raschka, 2007). Although it is difficult to make a direct comparison, these results may be due to the difference in measuring devices or performance levels of a national as opposed to a collegiate team.
There was no significant change in lean tissue for either males or females, in contrast to the results of Ratamess et al. (2012) with pre-season training for wrestlers, and the 4 week intensive training study of Argus et al. (2010). Results in this study may reflect the 8 weeks of primarily aerobic training, limiting opportunities for lean tissue improvement. In future studies, improvements that can maximize lean tissue through the introduction of weight training programs are therefore necessary.
Generally, at least 24 weeks of weight-bearing exercise are reportedly required to increase bone mineral density. The present study showed significant increases in bone mineral content and bone density, with exceptional results compared to those in the study by Guadalupe et al. (2009). However, since the number of subjects was small, caution is recommended in generalizing the results. Further research on bone density, considering factors such as gender, training intensity and duration, and body region, is necessary.
Physical fitness
Elite taekwondo athletes maintain a higher level of physical fitness than non-elite athletes. The pre-season training in the present study significantly improved the 50 m shuttle run and 20 m multistage endurance run results for males and females, but did not change sit and reach and standing long jump results. This may be a drawback of the current training program. Flexibility is important because differential scoring, favoring head points and lower extremity power during a competition, works adversely in a first-to-score golden point system during overtime (Kim et al., 2015). Therefore, sufficient stretching time before and after the match is necessary to improve the range of motion of joints, and readjusting the training program to improve power should be helpful.
Anaerobic capacity and Isokinetic muscle strength
An increase in lean mass requires at least 2 months of training, and an increase in muscle strength, resulting from a short period of training, is reportedly the result of neural adaptation. Although the short training time of the present study did have effects beyond maintaining lean tissue, there was improvement in relative peak power and anaerobic capacity for males, and a tendency toward an increase in females. Weber et al. (2006) reported a 10% maximum difference in anaerobic capacity with respect to lean tissue, but this was not apparent in the present study. This contrasting finding demonstrates that relative peak power and anaerobic capacity may increase without a significant change in lean body mass; however, the results would have been better had there been an increase in lean tissue (Argus et al. 2010).
The measurement of extensor and flexor strength in taekwondo athletes is an important indicator for monitoring training effects, and is a widely used objective evaluation method with good reproducibility (Coburn et al., 2006; Kim et al., 2011). Scoring, in 2-min, 3-round taekwondo matches requires muscle strength in the lower extremities; with at least 4–6 matches in a day, muscle endurance is also very important.
Isokinetic training results of knee joints before and after the pre-season training in the present study show that, except for left and right flexor angular velocity at % BW 60°/sec, left and right extensor angular velocity at % BW 60°/sec increased significantly for both males and females, representing improvements in extensor strength. There was also a significant increase in left and right extensor angular velocity at % BW 180°/sec for both males and females, thus showing improvements in extensor endurance; however, left flexor angular velocity at % BW 180°/sec significantly decreased, thus showing a decline in flexor endurance. A significant decrease in left flexor angular velocity at % BW 180°/sec, and a tendency toward decreasing flexor strength at an angular velocity of % BW 60°/sec, can be explained by the composition of the training program in the present study; training was good for the development of the quadriceps, through running and jumping, but not effective for the development of the hamstring, in which flexor muscles play a relatively important role.
In taekwondo, kicking velocity of the leg is as important as folding velocity; one must fold the leg after making a kick, using the flexor as quickly as possible, to make the following kick quickly and accurately. Therefore, supplemental activities that can strengthen the flexor muscles, such as weight training with leg curls, or resistance training using elastic bands, is necessary, and annual program modifications during pre-season training evaluations should be conducted.
In addition, although there was no increase in lean tissue, increases in left and right extensor angular velocities at % BW 60°/sec and % BW 180°/sec were possibly driven by neural adaptation, resulting from the combined action of muscle and a neural factor. In this regard, further detailed studies are necessary (Barnes, 1980).
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