APPLICATION OF PHYSICS IN TAEKWONDO

CHAPTER 1

1.0 Introduction

Taekwondo is much more than just a physical activity. The teaching of the art of Taekwondo has long been carried out with its entire culture and philosophy, and this will guide your interactions with others both within and outside of Taekwondo practice. The Taekwondo School is like a large extended family. Everyone looks out for everyone else, with senior students exercising the most responsibility. We don’t judge others, but accept them and help them progress and grow not only in the martial arts, but at school, work, and in the community. In Korean, tae (태, 跆) means "to strike or break with foot"; kwon (권, 拳) means "to strike or break with fist"; and do (도, 道) means "way", "method", or "path". Thus, taekwondo may be loosely translated as "the way of the foot and the hand."

The ability of force control to break boards or bricks for testing, training and martial arts demonstrations with bare hands or feet used to be associated with special, sometimes regarded as supernatural. The first attempts made at delivering a scientific biomechanical description of the techniques performed in martial arts go back to research projects conducted in the 1970s and 1980s (Vos and Binkhorse, 1966; Blum, 1977; Walker, 1975). Those studies described kinematic aspects of strikes and analyzed the process of breaking hard objects with bare hands shown in Fig 1.

The front kick was analyzed in several aspects (Hwang, 1987), namely a) hip, knee and ankle muscle torque arrangement, b) sequence of actions of the dominant muscle group, c) muscle contraction type, and d) range of movement in regard to the efficient muscle torques applied. It was observed that in case of the high front kick thigh deceleration takes place as a result of actions dependent on the initial movement in the lower extremity and not the braking action as such (Sørensen et al., 1996). The roundhouse kick was also analyzed by several researchers. The mean roundhouse kick execution time was 0.35 and 0.30 seconds for male and female athletes of the Singapore top taekwon-do athletes (Boey and Xie, 2002). However, no connection between the shortest trajectory and peak velocity was found. The mean maximum velocity of this kick is between 12.84–16.26m/s (Pieter and Pieter, 1995). Other researchers’ interests concerned the acceleration of the center of gravity, changes in the angles of body segments as well as changes in the momentum during execution of the roundhouse kick (Lee et al., 2001).

Description and analysis of a sports technique in relation to appropriate rules of biomechanics and with regard to its efficiency comprise the fundamentals of technical training which is directed at enhancing sport performance. This problem is of great importance in taekwondo, where a single strike might reveal the winner. In the Olympic Games, taekwondo has been limited to sports combat whereas the traditional version of taekwon-do sports competition (World Taekwondo Federation) comprises four competitive events, i.e. sparring, patterns, power tests and special techniques (General Choi, 1983; 1995).

1.1 Korean Terminology for Taekwondo

There are two different numbering systems that are used by Koreans. The first numbering system is used when counting, or when only speaking of the numbers themselves. The first ten numbers in this system are as follows; and the other numbering system (which is of Chinese origin) is used in most other cases and is often used where Americans would use ordinal numbers (such as "first", "second", etc ...). For example, this second numbering system is used when describing a person's rank: a first degree black belt would be an "il dan". The first ten numbers in this numbering system are as follows:

1	:	Hanah                                          1st  :  Il
2	:	Dool                                             2nd   :  Ee
3	:	Set                                                3rd    : Sahm
4	:	Net                                                4th    : Sa
5	:	Dasot                                            5th    : Oh
6	:	Yasot                                             6th    : Ryook
7	:	Ilgop                                              7th   : Chil
8	:	Yadol                                              8th   : Pal
9	:	Ahop                                               9th   : Koo
10	:	Yool                                               10th  : Ship

The stress in "hanah", "dasot", and "yasot" is on the first syllable, in "ilgop", "yadol", and "ahop" on the second. In counting cadence in Taekwondo, this is so emphasized that the other syllable frequently almost disappears (e.g., "han", "das", "yos", "lgop", "hop", etc.).

1.2 Korean commands                     

In taekwondo, Korean language commands are often used. Korean numerals may be used as prompts or commands. Often, students count in Korean during their class, and during tests they are usually asked what certain Korean words used in class mean. These words are fairly common amongst taekwondo schools, but accuracy of pronunciation can vary greatly.

Romanization	Hangeul	Hanja	English
Cha ryeot	차렷		Attention
Gyeong rae	경례	敬禮	Bow
Ba ro	바로		Return
Shi eo	쉬어		At ease (relax)
Hyu shik	휴식	休息	Rest period (break)
Ki hap	기합	氣合	Yell (shout)
Jun bi	준비	準備	Ready
Shi Jak	시작	始作	Begin (start)
Gal lyeo	갈려		Break (separate)
Gye sok	계속	繼續	Continue
Geu man	그만		Finish (stop)
Dwiro do-ra	뒤로 돌아		About face (180 degrees)
Hae san	해산	解散	Dismiss

1.3 Taekwondo Five Tenets

The tenets of Tae Kwon-Do should serve as a guide for all students of the art.

1.4 Courtesy:

Tae Kwon-Do students should attempt to practice the following elements of etiquette:

1. To promote the spirit of mutual concessions.
2. To be ashamed of one’s vice contempting that of other’s
3. To be polite to one another
4. To encourage the sense of justice
5. To distinguish the Instructor from student and senior from junior

1.5 Integrity:

In Tae Kwon-Do, the word integrity assumes a looser definition than the one usually presented in Weber’s dictionary. One must be able to define right from wrong, and have the conscience, if wrong, to feel guilt. Listed are some examples where integrity is lacking.

1. The Instructor who misrepresents him/herself and his art by presenting improper techniques to his students because of lack of knowledge or apathy.
2. The student who misrepresents him/herself by “fixing” breaking materials before demonstrations.
3. The instructor who camouflages bad techniques with luxurious training halls and false flattery to his students.
4. The student who requests rank from an Instructor, or attempts to purchase it.
5. The student who gains rank for ego purposes or the feeling of power.
6. The Instructor that teaches and promotes his art solely for materialistic gains.

1.6 Perseverance:

There is an old Oriental saying “Patience leads to virtue or merit. One can make a peaceful home by being patient for 100 times”. Certainly happiness and prosperity are most likely brought to the patient person. To achieve something, whether it is a higher degree or the perfection of a technique, one must set his goal then constantly persevere. Robert Bruce learned his lesson of perseverance and tenacity that finally enabled him to free Scotland in the fourteenth century. One of the most important secrets in becoming a leader of Tae Kwon-Do is to overcome every difficulty by perseverance.

1.7 Self Control:

This tenet is extremely important inside the Do-Jang, whether conducting oneself in free sparring or in one’s personal affairs. A loss of self control in free sparring can prove disastrous to both student and opponent. An inability to live and work within one’s capability or sphere is also a lack of self control.

1.8 Indomitable Spirit:

“Here lie 300 who did their duty”, a simple epitaph for one of the greatest acts of courage known to mankind. Although facing the superior forces of Xerxes, Leonidas and his 300 Spartans at Thermopia showed the world the meaning of Indomitable Spirit. It is shown when a courageous person and his principles are pitted against overwhelming odds. A serious student of Tae Kwon-Do will at all times deal with the belligerent without any fear or hesitation at all, and with Indomitable Spirit, regardless of whosoever and however many the number be.

1.9 Aim: The aim of this study is to assess the application of physics in Taekwondo.

1.10 Objectives:

• To develop an appreciation for taekwondo as sport and as an art.
• To achieve physical fitness through positive participation
• To improve mental discipline and emotional equanimity
• To learn self defense and modern skills
• To develop a sense of responsibility for self and others.

CHAPTER TWO

2.0 Theoretical analysis of physics in Taekwondo

Martial arts, like any sport, can be resolved into physics. The principles of Taekwondo, the ancient Korean art of “kicking and punching”, is a clear example of the ways in which physics is applicable to biomechanics. The beauty of Taekwondo lies in the fact that every motion can be explained in physics terms. The principles of conservation of energy, torque, center of mass, and power are directly applicable to Taekwondo. Understanding these physics derivations and reasons can create stronger fighting and more applicably, self defense for a layman. Techniques in Taekwondo are often performed incorrectly due to laziness which results in a lack of appropriate force and power. Physics can explain why the way we are taught by our teachers truly is the best way to perform a technique, reinforcing the realization that when Taekwondo was first born in the jungles of Korea, the masters understood the supreme importance of physics. Firstly, there are some assumptions that must be made. The mass of an individual is constant. We will also assume perfect conservation of energy, with little or no energy transferring into heat

2.1 Breaking Bricks

Fig. 1                                                                                 Fig. 2

 

4 Concretes paving bricks broken with a knife-hand strike.

The power test involves breaking as many bricks as possible by way of using a variety of strikes comprising two hand strike techniques and three kicking techniques, one of which is the side kick. The side kick (in taekwondo terminology known as yup chagi) is a technique in which athletes tend to declare the highest number of broken bricks. Thus, it is bound to affect the final score in each competition.

The amount of kinetic energy of the hand/forearm when in motion (or the amount of energy that the hand/forearm can impart to the brick) is proportional to the square of its velocity; that is why the key ingredient to breaking the brick is to have the hand/forearm moving at a high velocity.

Now we present the quantitative explanation. Let’s denote the energy needed to break the bricks by Eb. The calculation makes use of the conservation of energy and conservation of momentum, and a couple of simplifying approximations. If we denote the mass of the hand and forearm by m and the velocity of the hand/forearm just before its impact with the board by V, then the kinetic energy K of the striking hand/forearm just before impact is:

                                                                                                                 (Eq. 1)

Suppose the impact has broken the bricks, and we denote the mass of the brick fragments (or brick) by M and the velocity of the brick fragments and the hand/forearm after the impact by U (making the reasonable approximation that the brick fragments and the hand/forearm are moving at the same velocity immediately after impact). We now make another reasonable approximation that the energy that was lost to heat from the impact is negligible; then conservation of energy implies                                                                                                (Eq. 2)

Because of Newton’s Third Law, for every action there is an equal and opposite reaction, if we consider the hand/forearm and board as the whole system, there was on the whole system no net force that affected the impact. Therefore, there is conservation of momentum, which implies

                                                           

                                            (Eq. 3)

Equation 3 implies

                                                    (Eq. 4)

Substituting U from eq. 4 into eq. 2 and solving for  gives rise to

                                            (Eq. 5)

Since we already know that Eb is about 5 Joules, we can substitute the mass of the hand/forearm (about 1.3 kilogram) and the mass of the bricks (about 0.5 kilogram) into Equation 5 to determine that V, the velocity needed at impact to break the bricks is about 5 meters/sec, or about 11 miles/hour.

High speed photography has shown that a non-martial artist who has been instructed to strike fast and aim at a position that is significantly lower than the actual position of the bricks can actually reach a maximum velocity of about 10 meters/sec, or twice the velocity needed to break the bricks, thus verifying our initial statement that a novice can break a pine bricks if he has been given proper instructions

2.2 Momentum      

The quantity of motion of a moving body, measured as a product of its mass and velocity p=mv

Question arises; as a taekwondo athlete, what could potentially caused you the greater injury; being attack by a light-weight, fast-moving taekwondo player, or being attack by taekwondo athlete, with double the mass but moving at half the speed.

This question involves forces that cannot be answered by directly applying Newton’s second law,

 

For example when two taekwondo athletes strikes dollyo chagi in opposite direction using open stance, they collides, what determines which athlete’s kinetic energy is released in the impact after collision? These two bodies can exert very large forces on each other for a short time.

From Newton’s second law for a body                                     (eq. 1)

Considering a body of constant mass m because      

Newton’s second law becomes                      (eq. 2)

Since the mass m is constant, the net force     acting on a taekwondo player equals the time rate of change of combination    , the product of the body mass and velocity. This combination is the momentum or linear momentum of the body.

Using    for momentum we have                                     (eq. 3)

The greater the mass m and speed v of a taekwondo player, the greater is its magnitude of momentum mv.

Hence Akwa Ibom State taekwondo athlete strikes axe kick at 2m/s have the same magnitude of momentum (mv) but different momentum vectors  because their directions is different.

Substituting (eq.3) into (eq.2) we obtain                                            (eq.4)

The net force (vector sum of all forces) acting on a body equals the time rate of change of momentum of the body.

According to (eq.4) a rapid change in momentum requires a large net force, while a gradual change in momentum requires less net force.

This principle is used in the design of electronic trunk guard (hugo), head guard and shine guard for safety to lose momentum within the short time of collision.

CHAPTER THREE

MATERIALS AND METHODS

3.0 Study Area

The study of this work was based on concrete paving bricks using knife-hand strike for the breaking technique and six (6) World Taekwondo Federation (WTF) athletes who are practicing taekwondo in Akwa Ibom State. The athletes are registered student in three known taekwondo schools, namely Rhodimos Taekwondo Sports Foundation, Akwa Ibom State Taekwondo Association and University of Uyo Taekwondo Club comprising 2 female athletes and 4 male athletes. The researched group included National Sports Festival Champions, South South Taekwondo Champions and other athletes who had practiced taekwondo for more than 4 years. They all train at most 3 to 4 times a week.

3.1 Axe Kick

Fig. 3                                                        Fig. 4                                      Fig. 5

In the Axe kick, the martial artist lifts his leg up, extends it high in the air, and then brings it back down, snapping the leg at the point of impact. In this case, it is very clear to see that the higher that the artist can extend his leg, the more energy he will have on impact, as
Potential Energy = Mass X Acceleration due to gravity X Height.

                        then the energy is conserved.

For the purpose of the experiment, they were asked to adopt the same starting posture (in Taekwon-do terminology called Niunja So Palmok Degi Maki) and perform the side kick three times. The analysis covered 18 attempts altogether. The structure of the movement is presented in Figures 6, 7, 8. In this case study HP Pavilion Entertainment PC system was projected into 3D screen for complex movement analysis produced by BTS S.p.A. company was used. The system comprised six cameras emitting infrared rays, which in real time localized the markers fixed to the athlete’s body. These markers reflected the infrared rays emitted by the cameras. The system facilitated recording the picture of the movement of the competitor’s body and evaluation of the kinetic data obtained. The picture was recorded with accuracy of 0.3 – 0.45 mm and frequency of 120 Hz. Obtained data concerning the movement and speed of characteristic points on the athlete’s body were analyzed, which allowed to specify the indicators which define the structure of space and time of the athlete’s movement. In the analysis of particular segments of the technique the following factors were taken into consideration: v_z - speed of the foot with regard to Z axis, v_y - speed of the foot with regard to Y axis, v_kz - speed of the knee with regard to Z axis, v_ky - speed of the knee with regard to Y axis, t_kick – time from the moment of foot take off to the moment of full extension of the kicking leg, t_total – time from the moment of the movement of the athlete’s body to the moment of full extension of the kicking leg, F_r – the ground reaction force of the plant foot.

Diagram of the side kick movement (in taekwondo terminology is yup chagi)

Fig. 4

Fig.5 General view presenting relevant joints and segments of the kicking leg.

Fig. 6 Yup chagi movement structure diagram – side view

                                                                          

3.3 Statistics

Correlation coefficients were determined between the foot and knee velocities and the kick duration time as well as the velocities of raising of the foot and knee. This correlation was verified at the significance level of p<0.05. All the statistical calculations were carried out with the use of MS Excel 2007.

3.4 Starting Posture

The athlete adopts the L-stance forearm guarding block (in Taekwondo terminology referred to as niunja sogi palmok debi maki) with the right foot moved forward. According to taekwondo rules (Choi, 1995) in this stance 70% of the body weight should rest on the back foot and 30% on the front one. Both feet should be slightly pointed inwards and the toes of the foot at the front should be lined up with the heel of the back foot. Both knees are slightly bent. The term ‘starting posture’ comprises information on the stance and the place where the attempted attack starts.

3.5 Shifting the back leg forward

The athlete moves the back foot forward in the direction of the intended impact. This results in a slight rise of the COG. The hands are held up in a guard. When the feet have touched the ground, the ankle joint tenses and the athlete energetically pushes the right foot off the ground.

3.6 Lifting the leg

As a result of the right foot take-off the force pushes the foot upwards. Further movement is facilitated by the muscles of the lower limb taking control over the movement. Thus, the knee and hip joints are extended. This phase witnesses the greatest velocity of the foot traveling upwards with the mean velocity being v_y= 5.10 m/s. On average it is in the 82% of the full leg extension when the foot reaches its peak velocity, whose mean is v_z= 5.65 m/s (Picture 4). The average time of lifting the leg until the moment of its full extension is 0.39 s.

Fig. 6 Plot of average change in foot velocity on y-axis against leg extension on x-axis while executing yop chagi in relation to z-axis.

Scale:  2cm represent 2.00units on y-axis

            2cm represent 20.00units on x-axis

Final phase

Fig. 7                                                                                        Fig. 8

 

The kicking foot is extended in the ankle joint. The athlete has had to balance his/her body in such a way so as to make sure that the foot planted on the ground has remained the only point of his/her body being in contact with the ground. Total time of kick execution (from the starting posture to the final phase) produced an average time of t=0.71 s.                                               The average values of the kinetic parameters are presented in Table 2.

Table 1.0

Biomechanical parameters influencing the efficiency of the kick

Variables	Average	Range
Velocity of the foot with regard to Z axis Vz [m/s]	5.92	3.49/7.95
Velocity of the foot with regard to Y axis Vy [m/s]	5.25	3.39/6.30
Velocity of the knee with regard to Z axis Vkz [m/s]	3.21	1.20/5.05
Velocity of the knee with regard to Y axis Vky [m/s]	3.06	1.68/4.35
Time from the moment of the foot take off to the moment of the full extension of the kicking leg tkick [s]	0.35	0.29/0.63
Time from the moment of the movement of the athlete`s whole body to the moment of the full extension of the kicking leg ttotal [s]	0.72	0.46/0.89
The ground reaction force of the plant foot Fr [N]	1253	1003/1779

Table 1.1        Computation of mean six (6) Taekwondo athletes

Age (years)	Weight (kg)	Height (cm)	Gender
23	68.6	165.3	Female
26	72.4	160.8	Female
22	80.0	178.5	Male
29	79.3	180.0	Male
28	69.5	175.3	Male
30	78.8	170.0	Male
= 158	448.6	1029.9

Table 1.2

Physical characteristics means of 4 male and 2 female taekwondo athletes.

Variables	Athletes (n=6)	Range
Age(years)	26.5	20-30
Weight (kg)	78.0	68-80
Height (cm)	171.3	165-185

CHAPTER FOUR

SUMMARY/CONCLUSION

4.1 Summary

The velocity of the side kicks which Wilk et al. (1982) obtained when studying karate athletes (no particular karate style was specified) was between 9.9 and 14.4 m/s. In the research involving top taekwondo athletes Pieter and Pieter (1995) obtained the velocity of the side kick of 5.20–6.87 m/s. The mean maximum velocity of the side kick determined in that research was 5.65 m/s. Such results show a certain difference in velocities obtained by karate and taekwon-do athletes. It can be assumed that such differences can be attributed to different ways of execution of the kick in those martial arts.

Fig. 9 shows the correlation between maximum foot velocity and maximum knee velocity during execution of the side kick (r=0.72). This dependence shows that higher knee velocity increases the velocity developed by the foot. This means that working on improvement of the side kick technique aiming at increasing foot velocity attention needs to be paid to knee velocity which needs to correspond to the movement of the foot. Graph 2 presents the correlation between the duration of the side kick and the maximum velocities of the knee v_ky (r=−0.59) and the foot v_y (r=−0.86) in relation to axis Y. This implies that a short duration of the side kick will depend on the maximum velocity achieved by the knee and foot in the leg lifting phase. The total duration of the side kick comprises the time between the starting posture and shifting the back leg forward as well as the leg lifting time. These factors are presented in Fig.10

Fig. 9

Correlation between maximum velocity of the foot and knee during the side kick

Fig. 10

Correlation between the velocity of the traveling foot (v_y), knee (v_ky) and kick execution time (t_total)

Fig. 11

Factors affecting the side kick execution time

The conducted measurement of the absolute force of the side kick showed that taekwon-do athletes obtained values ranging from 390 to 461 N (Pieter and Pieter, 1995). However, there was no information provided on the distance from the aim of the impact which they covered while executing the kicks. That research also shows that there is a strong dependence between the force of the side kick and the weight of an athlete. Not only does a greater weight add to a greater force, but it also results in an increase of the kinetic energy (Pieter et al., 1987). Knowledge of these facts proves considerable importance in board breaking as in this particular case the time and a high level of average energy production are not as important as the maximum energy at the very moment of the impact (Stull and Barham, 1990).

Well adjusted distance affects the force of the kick which can be obtained (Falco et al., 2009). The mean maximum velocity calculated in the research was achieved at the length of the leg equal to 82 % of the maximum leg extension. This length can be regarded as the optimum value in this kicking technique making it possible to achieve maximum dynamics of the kick. Thus, using the kinetics of the kick in full is only possible in cases when the aim of the impact is located at the optimum distance given for this particular kind of kick. According to the equation

                                                                       

 it can be assessed that at the moment when the velocity of the foot reaches the maximum value, the force of the impact will also be the greatest (Hay, 1993; Wąsik, 2007). The force of the kick assessed as presented above with the mean maximum velocity and mean athlete’s body weight (provided the total athlete’s body weight is engaged in the movement) would amount to F ≈ 1020 N. In case of such assessment a mistake in the distance which equals to 10 % would mean a decrease in the power of the kick down to F ≈ 512 N.

Thus, a precise assessment of the distance along with the correct time of the moment of impact constitute a very important aspect of information for taekwon-do athletes, especially those taking part in power breaking events, where the aim of the impact is a fixed board.

4.2 Conclusion

In conclusion, board breaking requires great maximum velocity at the moment of impact, which is usually achieved at the cost of attack duration (Stull and Barham, 1990). However, in cases in which the aim is to obtain points in sports competition, athletes will need to focus on reducing the duration of the kick and increasing mean kick velocity.

In pursuit of perfection, further research will most certainly be required in order to determine duration of the side kick, influence of reaction time on the achieved power of the kick as well as analyses of taekwon-do kicks during real-time fighting, which will make it possible to specify which variables of this particular kick affect its efficiency. The present study is an introduction to further more detailed research into this particular issue. The results and discussion presented herein can be regarded as comparative material for other researchers.

4.3 Recommendation

In Taekwondo every techniques is generally used in all types of martial art, the human parts of the body are all weapon in the sense that they martial arts practitioners used them in their daily lives to defend their life and build the most peaceful world.

Exercising the body, using taekwondo techniques promotes healthy living. Taekwondo therapists also contribute to the reduction of daily stress and generate new thoughts of mind without stress. Taekwondo is useful in sport, security sectors, and schools to develop mental and physical body.

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