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.
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
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...