1. Karate: Front vs. Side Kick
Jaimin E. Sin
Biol 438

2. Objectives Breakdown techniques What makes a hard collision?
Understanding mass, velocity, energy
Why are side kicks not observed as frequently in sparring as front kicks?
To hit as hard as possible, need to strike as fast as you can.
Mass is also an important component of force and momentum, so the greater the mass, the stronger the strike.
Therefore, it is important to not just use the pushing of your leg, but also include motion of the hips to throw mass of your body behind the kick.

3. History Karate = “empty hands” Originated from Okinawa, Japan
4 main styles
Goju-ryu
Shito-ryu (1928)
Shotokan (1938)
Wado- ryu (1939)

4. Newton’s First Law of Motion
Property of inertia
Body stays at rest unless acted on by an outside force
Need to spend energy to overcome the inertia of the standing leg
The spent energy is stored momentarily as potential energy within the thigh, calf, and foot
Potential energy is converted to kinetic energy when the leg is pushed to extension

5. Front Kick Technique: Step 1
Lock stance in place with the front leg you’re kicking with front leg forward. Recalibrating your center of gravity so that you have an imaginary tripod extending from your body

6. Step 2
Lift knee up, locking the hip to maintain balance on your one foot, storing PE

7. Step 3
Thrust knee out in an extended swinging motion, converting the stored PE into KE, and striking with the ball of your foot, not only to avoid injury, but if you decrease the surface area of contact, that’s going to impart more energy per area than when you strike with the full flat part of the foot, and cause more damage.

8. Step 4
Very important to recoil back into original stance as fast as possible or you will get hit by your opponent because you become most vulnerable to counterattacks the second that you have finished your attack
It happens really quickly but in karate and as in any other sports, timing and strategy is incredibly important
You can see the white arrow pointing to the left- not supposed to do that! (33 sec)

9. Full Motion of Front Kick

10. Muscle Groups for Front Kick
Vastus Lateralis and Medius (thigh)
Gluteous Maximus (butt)

11. Most power comes from the gluteus maximus.

12. Side Kick Technique: 5 Steps
1. Fighting stance 2. Bring knee up angled at 45 degrees 3. PIVOT + extend leg at knee; the pivot serves to contribute more mass behind the strike, 4. Bring leg back 5. Back to fighting stance, again…didn’t do that; as you can see from the video, you can begin to see why using a side kick is not a good idea when sparring because although you can deliver a strong blow, you land hard on your feet

13. Muscle Groups for Side Kick
Rectus femoris (thigh)
Vastus Lateralis and Medius (side thigh)
Gluteous Maximus (butt)
Rectus abdominus (abs)

15. Hypothesis 1
Pivoting in the side kick allows for more body mass to go behind the kick
Will bring about a greater velocity of the foot than in a front kick

16. Front Kick

18. Side Kick

20. Determining Peak Velocities Equation for overall velocity=X2+Y2= Z2 Overall velocity= Z1/2
Front Kick
Side Kick
X= 5.33 m/s Y= 3.20 m/s Z= 6.22 m/s
X= 4.21 m/s Y= 3.15 Z= 5.26 m/s

21. Analysis
In the front kick, because you have a linear motion where your hip abduction is in line with knee extension, this is going to lead to a simple forward motion
In a side kick, abduction of hip and knee joint motions are not coplanar
In graph, knee stabilization occurs after reaching peak velocity
Hip abduction moving perpendicular to knee extension is going to take away from the velocity of the kick
- So some of the energy is being lost to knee stabilization when all the energy should be focused on speeding up the foot

22. Hypothesis 2
Side kick will exert greater energy of impact because more body weight is thrown behind the kick
Objective: Measure the energy imparted in a side kick vs. a front kick

23. Method of Study
Assuming conservation of energy, the sum of potential and kinetic energy remains constant
KE1+PE1 = KE2+PE2
Punching bag simulates the movement of a pendulum
When the swing of the bag reaches max height, all PE and no KE
At the point when object is aligned with fixed pivot, all KE and no PE

25. Punching Bag delta Height for Front Kick
delta h (or change in y)= = m

27. Punching Bag delta Height for Side Kick
delta h= = m

28. Energetic Calculations
Mass of punching bag= 150 lbs = 68 kg Motion of bag equivalent to swing of a pendulum When bag reaches crosses pivot point, KE1=1/2mv2 and PE1=0. When bag reaches maximum height, KE2=0 and PE2= mgh Using KE1+PE1 = KE2+PE2 Equation: KE1 =PE2 ½mv2 = mgh ½v2 = gh

29. Front Kick
Side Kick
hbag= m
vbag= 1.16 m/s
KE1 = PE2 = mgh
(68kg)(9.8m/s2)(0.069)= 46 Joules
hbag= m
vbag= 1.20 m/s
KE1= PE2 = mgh
(68kg)(9.8m/s2)(0.073)= Joules

30. Hypothesis 2 Analysis: 2 explanations 1. 2.
Side kick imparts more energy because more body mass is going into the kick
This can be attributed to the pivot that occurs in the technique
How much of body mass is going into the kick? 2.
Results don’t match with findings from Hypothesis 1
Possible reason: Non-conservative force
Measured downward swing and not upward swing
Energy rebounded back to kicker than completely go into punching bag

31. Conclusions
A side kick is not utilized in sparring competitions due to its cumbersome nature
slower velocity, possibly due to opposing joint motions
momentum generated makes it difficult to recoil, and vulnerable to counterattack
To hit as hard as possible, need to strike as fast as you can
Mass is also an important component of force so the greater the mass, the harder the strike
Therefore, it is important to not just use the pushing of your leg, but also include motion of the hips to throw mass of your body behind the kick
In matches, the side kick motion used usually as a fake out in preparation for a roundhouse kick

32. Problems with the Study
Form/ techniques
Heavy punching bag
Shoes
Push off
Less flexibility
Assume conservative system with no friction or air resistance
Limitations in measurements
Vertical force plates
3D motion analysis
Mass distribution for different kicks
Less flexibility- less range of motion to generate peak velocity

33. Questions for further study
Inter-joint coordination of kicking leg to produce velocity (3D motion analysis)
Focus more on the extent of pivot on standing leg of a side kick
Examine velocities performing technical variations of the same kick
Measuring kicking velocities and energy impact in people with different masses
1. How to improve the strength of the kick

34. Sources
Kim, Y. K., Y. H. Kim, S. J. Im Inter- joint coordination in producing kicking velocity of Taekwondo kicks. Journal of Sports Science and Medicine. 10:

35. Questions?