A Biomechanical Analysis Of The Roundhouse Kick

Anatomical Analysis

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