Biomechanics of Kumite Style Gyaku tsuki in Karate

In karate sparring (Kumite), punches are used more than kicks to score points. Among these punches, the gyaku tsuki is the most commonly used punch. The objective of the punch is to hit the target at a medium range in a very short time producing maximum force. In this study we propose to design a new standalone system to measure the speed and force generated by the punch. Finite Element Analysis (FEA) has been performed to determine why the specific sensor arrangement works efficiently, distributing the force on all sensors. Since punches are executed within a few hundred milliseconds, identifying the punch which is faster by even a few milliseconds would give an edge in competitions. Two types of gyaku tsuki in Kumite stance were compared for speed and force generateda normal gyaku tsuki and a gyaku tsuki without rotating the fist.


Introduction
Karate training is divided in three main parts-kata (forms), kihon (basics) and Kumite (sparring). The strikes in karate are mostly linear [1] i.e. they travel in a straight line which makes them quick. Mass of the leg is about 20 % while that of the arm is just 5% of the total body weight [2]. This difference in mass is why kicks harder to aim but are more powerful. In competitions, scoring precise points quickly is emphasized than delivering powerful blows. Hence, punches find a very important place in the karate Kumite arsenal. Gyaku tsuki also known as the reverse punch is the most frequently used punch in competitions. The objective of the punch is to hit the target at a medium range in a very short time producing maximum force. From normal fight stance, the attacker athlete lowers his centre of mass while extending his stance lunging towards his opponent and extending his punching arm forward executing the punch in the open unguarded part of the opponent's abdomen [3]. This punch is preceded by a series of body movements namely the twisting of hips, shoulder rotation.
The peak velocity of the joint preceding a joint, aids in further increasing the joint's peak velocity. Rathee et al. [4] conducted a study for the parameters required for breaking a wooden board by two karatekas. For inelastic collision, Deformation Energy (DE) is the energy lost to deformation. It is given by Punching is studied as a kinetic link principle where the joints' movement occur in a sequential order. The peak velocity of the next distal joint exceeds the peak velocity of the preceding proximal joint [5]. Since the pelvis and trunk of the body have more mass these body parts while rotation have greater moment of inertia.
During movement, the (relatively) larger muscles attached to these joints contract and achieve their peak angular velocity earlier than the next segment.
After reaching their peak velocities, these muscles relax transferring this velocity to the next distal segment [6]. Dyson et al. [7] did a study of the muscles involved in a boxing punch to understand the role of major individual muscles in the punch. It was found out that the gastrocnemius was the first muscle to be activated during a punch due to the action of moving the body forward by plantarflexion. The rectus femoris and biceps femoris were activated next to extend the knee and hips. These were followed by the trapezius, deltoid muscles and biceps brachii to flex the elbow shortly, followed by extension of the elbow done by the triceps brachii and flexor carpi radialis in the forearm to execute the

Materials and Methods
The method used by Falco et al. [14] to measure the force of kicks in taekwondo was adapted and modified into a standalone system which was able to detect the speed and force of a gyaku tsuki punch while displaying it in real time. Two wooden circular plates of wood were cut in a dimeter of 25cm and sensors were placed between them to detect force applied on the wooden platform. The force is distributed homogenously throughout the wooden surface and recorded by the sensors. The sensors used were Tekscan Flexiforce A201 force sensors [16]. Nine sensors were arranged along the sides of an equilateral triangle of length 15cm. Three sensors were arranged along the midpoint of each side of the triangle as shows in

Punch Speed Detection Module
To detect the punch speed, two lasers (KY-008 red dot diode

Test Conducted
One participant was chosen for this test-weight 72kgs, about 7 years of experience in karate. The participant was asked to punch the system with normal gyaku tsuki and gyaku tsuki without rotating the fist both in Kumite style as shown in Figure 5. All these punches were done from a stationary position without any stepping motion.
The forces and speed of these punches was to be determined to analyse the best type of gyaku tsuki to be used in competitions. The  Wayne State University IRB cleared the participant for the tests.
The participant was asked to stand at a comfortable arm's length for punching the system and to maintain the Kumite stance to maintain balance since punching on the rigid wall tended to throw the participant off balance. Figures 5 & 6 shows the initial, middle and final position of the fist while punching the two punches. For punching through various speeds from 1 to 6m/s, different force values were calculated and plotted. While punching the participant was instructed not to be bias towards any specific punch type.
The participant was also instructed not to compress the wood as the algorithm would not accept that as a valid reading. Any value for punch which would have a plateau at the peak value would be rejected.

Results
Falco et al. [14] had initially designed this system to measure  Tests were conducted to check the experimental values when punched with both the types of punches. Figure 8 shows the curve of force vs speed of both the punches while Table 1 shows these values. After checking the force trend generated by these punches, both the punches were tested for achieving maximum average speed. Table 2 shows the tests conducted to calculate the maximum average speed that can be attained by both these punches.

Sensor Arrangement
The sensor arrangement adopted by Falco et al. [14] was As seen from (Figure 7), sensors record force more evenly when punched at the centre than away from the centre. In case 2, there is a big gap between the highest and lowest readings on the sensors since it is closer to a certain group of sensors than the other. In case 3, the gap is higher due to the introduction of negative forces.
Since the load extends in the area not supported by the sensors, an imbalance is created and the sensors on the other end display a negative force. The negative force acts by pushing the board away from the sensor. The resultant of all these forces is 2kN. In case 4, negative forces are higher because the board is tilting a considerable distance on one side.   Table 1 and Figure 8 show that the force generated by the normal gyaku tsuki is higher than its counterpart when punched at the same speed. At all speeds the normal gyaku tsuki's force is 6.67 % to 12.16 % higher than the gyaku tsuki without fist rotation. Diacu, [22] showed the mathematical proofs for increase in generation of Kinetic Energy when performing a normal gyaku tsuki. Considering a 70Kg person punching at a speed of 5.5m/s, the mass of his arm would be 5 % of his total weight. He rotates his fist by 180 degrees or 5π radians and the radius of his fist rotation be 5cm or 0.05m. During translational punching, the generated kinetic energy, Ek and rotational Energy (Er) were calculated to be 52.94J and 1.079J respectively.

Comparison of Punch Force
This proves that the force generated by the gyaku tsuki is higher than the gyaku tsuki without rotation. Research on the change in moment arm during pronation and supination has been done by Bremer, [23].

Comparison of Punch Speed
Maximum attainable speeds of both the punches were checked in Table 2 to determine whether either punch can punch with higher speed than the other. It was seen that the gyaku tsuki without the

Conclusion
The specific design was chosen because it was used by Coral Falco et. al. for their study to find out the force of a taekwondo kick.
Their system has been modified by adding a speed detection module and a graphic LCD which displays the punch speed, force, force time curve of the punch type in real time. This system can be used to determine all these parameters for any type of punch except for any punch which has a pushing movement. Any movement aiding the punch like the yori Yashi (forward step)-gyaku tsuki/ kizmi tsuki can be used too. The system has a relatively low sampling rate hence punch speeds upto only 8.33m/s are recorded. The curves obtained from the punches prove that with increase in punch speed, the force of the punch increases. By simulating the force distribution on all sensors by punching in different areas of the wooden platform, it was seen that the sensors record force when the whole punch lands inside the area of the triangle formed by the sensors. As per the results of speed and force obtained by the two punches obtained in Table 1 and the pattern observed in Figure 8, the normal gyaku tsuki delivers a higher force upon impact when punched than the gyaku tsuki without fist rotation.
The group of muscles involved in pronation motion of the wrist and forearm while performing the normal gyaku tsuki generated a higher moment which leads to higher force generation. It is in accordance with its speed being slightly higher than the latter There are some techniques that could be followed to increase the speed of any punch. Rotating the pelvis transfers the increase in angular velocity to the arm. Studies done previously have proved that gyaku tsuki punched from near the waist rather than starting midway produces more linear velocity of the wrist [24]. Also, faster the opposite arm is retracted, faster is the punch [6,25]. There have been other studies stating different force values of punches and kicks in the past. The absolute force value of the punch is not obtained in this system since calibration of the system was done by placing static loads whereas the punch is a dynamic load. Moreover, since the sampling rate is less at 134Hz, it is not able to record any higher peaks which could have been missed. Using this very system repeatedly would give the results in real time and the user can mark one's progress through practice and set short and long-term goals. Determining the kinematics of the arm would provide side by side comparison of the arm velocity changes w.r.t time and more conclusions could be drawn from that. EMG can be recorded of the muscle groups to find the function of individual muscle and groups in a punch. More participants should be tested to strengthen the claim.