Analysis of the Gyaku-Tsuki
One of the fundamental Karate techniques is the gyaku tsuki (reverse punch, Fig. 1). It can be aimed at three levels: jodan (head, neck), chudan (ribs, solar plexus, kidneys, abdomen) and gedan (lower part of the abdomen, genitals). Chudan is considered in the present example.
The stance chosen for this test is the zenkutsu dachi: it is a front stance, with the forward knee bent, the rear leg straight and both hips and shoulders facing forward. The rear foot is dorsiflexed at the ankle and directed forward and outward. The maximum angle between the foot and the trace of the sagittal plane on the ground for an optimal posture is 30°. Weight distribution on front and rear feet is 7:3.
At rest, the fist is placed on the hip, just above the belt, with the palm facing upwards. From this position an ascending rectilinear trajectory is followed and simultaneously a 180° rotation about the longitudinal axis of the forearm is performed. At the instant of impact the palm faces to the ground.
The energy of this punch comes from the combination of the rotation of the hips with the thrust of the arm; therefore the first must slightly anticipate the second.
Fig. 2: Kinetic energy released by the athlete performing gyaku tsuki
Fig. 2 shows the kinetic energy (KE) released by the athlete during the execution of the gyaku tsuki. In the starting position (oi tsuki in zenkutsu dachi, Fig. 1a and Fig. 1e) the athlete stands still and her levels of KE, hand speed and pelvis angular velocity are almost null (cfr. following figures).
In the middle of the pelvis rotation (Fig. 1b and Fig. 1f) the rotational kinetic energy (Tr) reaches its maximum value (11.37 J). The corresponding peak of the pelvis angular velocity is 11.96 rad/s (Fig. 4). As expected, the rotation of the hips slightly anticipates the extension of the arm.
Fig. 3: Speed of the hand performing gyaku tsuki
Fig. 4: Angular velocity of the pelvis around the local Z axis
During the pelvic rotation, the excursion of the punching arm begins: in the middle of its trajectory (Fig. 1c and Fig. 1g) the athlete releases the largest total KE (56.84 J at 4.42 s). The peak of KE is almost coincident with the maximum hand speed (5.81 m/s, Fig. 3).
Right after the instant of maximum KE, the pelvis angular velocity reaches a negative peak, lower than the previous one (Fig. 4). It is related to the small additional rotation of the trunk, due to its inertia: the athletes goes over the correct angular orientation of the hips and then automatically corrects her posture, aligning the hips exactly on the X axis.
In the final posture the arm is totally extended (Fig. 1d and Fig. 1h): the athlete stands still and all the kinematic and kinetic parameters are almost null again.