|
Tae Kwon Do is a Korean, unarmed martial art and is best known for
its kicks (Park, 2001). The roundhouse kick is a turning kick and
happens to be the most commonly used kick during competition (Lee,
1996). For this reason, the roundhouse kick will be analyzed in
reference to sparring competition.
The roundhouse kick, a multiplanar skill, starts with the kicking
leg traveling in an arc towards the front with the knee in a chambered
position (Pearson, 1997). The knee is extended in a snapping movement,
striking the opponent with the top of the foot. One’s goal would be to
make front torso contact with the kick, while avoiding leaving one’s
self open to a counter strike.
The movements that comprise the roundhouse kick begin with a
fighting stance: both feet on the ground, toes pointing straight ahead,
back foot turned outside up to 22 degrees, front foot approximately 1.5
the distance of one step from the back foot, both feet approximately
one length of one foot apart, extension of both legs, slight rotation
of the torso in the direction of the back leg, fists held in front of
the chest, flexion at the shoulders by about 45 degrees, flexion at the
elbow by about 60 degrees, and flexion of the fingers.
One initiates the preparatory phase of the roundhouse kick from the
fighting stance: rotation of the torso in the direction of the front
leg, flexion and abduction at the hip, flexion at the knee of the back
leg which brings the knee to the torso and maintains a minimal relative
angle at the knee to the thigh, plantar flexion of the foot, and
lateral flexion of the spine toward the ground away from the kicking
leg (Table 1).
The fighter is then ready to initiate the movement phase: extension
at the knee with a relative angle to the thigh of about 180 degrees,
lateral rotation of the grounded foot between 90 and 120 degrees, and
additional lateral flexion of the spine.
After attempting to make contact with the opponent, the fighter
immediately follows up with the recovery phase: flexion at the knee,
lateral flexion of the spine opposite the aforementioned direction,
during a slight rotation of the torso, extension of the hip, and
dorsiflexion of the foot. This brings the fighter back into the
fighting stance with the opposite leg in the front and is now ready to
perform the next strike or counterstrike.
Mechanical Analysis
One must obtain optimum speed and accuracy in order to fulfill the
purpose of making front torso contact without allowing for a
counterstrike to one’s own front torso (Hamilton, 2002). In a sparring
competition, a competitor must also avoid falling to the ground, thus
balance is also included among the mechanical objectives.
The roundhouse kick is an angular movement, so when taking optimum
speed into consideration as an objective, it is understood that angular
velocity, denoted as z, is equal to the angular displacement, denoted
h, divided by the change in time, denoted Dt (Hall, 1999).
z= h
Dt
So, one would obtain an optimum velocity by increasing the distance
over which the position changes of the kicking foot over a minimal
amount of time. A kick can be performed at a high velocity when the
aforementioned technique is used, creating an ideal circumstance for
angular displacement, where the radius of a given point, the foot, on a
rotating body, the lower leg, and the axis of rotation, the knee, is
minimal, thereby reducing the linear distance covered which can in turn
be performed in a minimum period of time (Hall, 1999).
Another factor worth consideration is the moment of inertia, denoted
as I, or the tendency of a rotating body to resist change in its state
of motion which is based on both mass, m and the distance over which
the mass is distributed from the axis of rotation, denoted as r (Hall,
1999).
I=mr2
This concept is key in the technique of the kick as the low relative
angle of the knee to the thigh in the preparation phase reduces the
radius of gyration, denoted as k, in reference to the lower leg and
foot (Hall 1999).
I=mk2
These factors, the angular velocity of the lower leg, distribution
of the mass of the leg and foot, with respect to the axis of rotation,
the knee, and the mass of the leg and foot itself, all build to form
the angular momentum, denoted as H (Hall, 1999).
H=mk2z
However, because the primary goal is to achieve optimum velocity,
optimum momentum is obtained through angular impulse. The series of
movements before contact with the target attempts a kinetic chain with
an efficient sequence of movements previously noted in the description
of the preparatory phase (Champion, 2002). The internal muscles move
first, such as the serape and spinal flexors and rotators, out to the
Gluteus maximus, to the Rectus femoris, transferring the large body
movements from the trunk to the smaller body segments of the foot. If
the movements are timed correctly, one will have maximum speed upon
reaching the next movement, until the point of application (Champion,
2002).
Another valuable aspect to consider is drag, which is a resistance
force slowing down the motion of the leg and foot through the fluid
medium, air (Hall, 1999). The most relevant form of drag here is
surface drag, where the size of one’s leg and the increased surface
area created by the traditional uniform, in addition to its texture
play prominent roles in decreasing the velocity of the kick.
Once the kick has been executed, impact must be taken into account.
The result of the impact of one’s foot with the opponent’s front torso
largely depends upon the velocity of the kick, the velocity of the
opponent if in motion at the point of contact, the size and shape of
one’s leg and opponent’s front torso, the environmental temperature,
and elasticity of protective gear. It is difficult for a fighter to
judge impact if his or her opponent is in motion. If one or the
opponent is hot and is sweating through the protective gear, it will
become more plastic, reducing the rebound and influencing the velocity
of the movement in the recovery phase.
The other mechanical objective, balance, is in other words the
ability to control equilibrium (Hall, 1999). A fighter maintains
balance when offsetting his or her center of gravity while flexing at
the hip and knee by countering this redistribution of mass by lowering
the head and torso. Stability is related to this concept of equilibrium
and is defined as the resistance to disruption of equilibrium (Hall,
1999). During the starting and ending position of the roundhouse kick,
optimum stability achieved with the footing noted previously in the
discussion of the movement phases, which maximizes the base of support.
Whether or not a fighter can stay on his or her feet weighs heavily
upon the component of friction too. If there is minimal friction
existing between the supporting foot when performing the kick and the
ground surface, a fighter will have a tendency to fall frequently. If
there is too much friction present, the fighter may be restricted in
his or her chain of movements.
Error Detection and Prescription
Those new to the practice of Tae Kwon Do may tend to shy away from
removing socks during a lesson. A teacher will insist upon removal of
socks or the student will soon learn first-hand about the effects of
little friction between the foot and the ground surface. A simple
correct here is to practice barefoot or to invest in appropriate
sparring footgear.
Beginners also tend to skip flexion at the hip and knee before
extending at the knee, instead going from the fighting stance to the
flexion of the hip with the knee fully extended right to the target.
This, of course, slows down the kick considerably because of a number
of reasons. This performance error results in a greater linear distance
covered by the foot with the rotating body, the fully extended leg.
There is a greater moment of inertia with the increase in mass of the
segment in this one motion. Surface drag is also increased in this one
motion as the surface area has increased. This can be corrected simply
by instructing the beginner of the correct technique in flexing the
knee in addition to the hip before extending at the knee.
One other common error that occurs with beginners is an extension at
the elbows as one kicks. This is a natural action one takes in order to
maintain balance. However, a fighter must not leave the front torso
open to a strike, so this reaction must be corrected by lowering the
torso and head.
References
Champion, L., Introduction to Biomechanics, Lecture, Fitchburg State College, Fitchburg, MA, March 28, 2002.
Hall, S.J., Basic Biomechanics, McGraw-Hill Comp., New York, NY, 1999.
Hamilton, N., K. Luttgens, Kinesiology, Scientific Basis of Human Motion, McGraw-Hill Comp., New York, NY, 2002.
Lee, K.M., Tae Kwon Do, Techniques and Training, Sterling Publishing Comp., New York, NY, 1996.
Park, Y.H., Tae Kwon Do, Lesson, Master Park’s Tae Kwon Do College, Lunenburg, MA, 2001.
Pearson, J.N., Kinematics and Kinetics of the Taekwon-Do Turning
Kick, A dissertation submitted in partial fulfillment of the
requirements for the degree of Bachelor of Physical Education with
Honours at the University of Otago, Dunedin New Zealand, 1997.
|
|
|
(0 vote)