Learn yoko-geri-kekomi in karate: chambering the knee, pivoting the supporting leg, a straight thrust line, recoil. With milestones, WKF scoring and knee notes.
The honest answer: yoko-geri-kekomi is a side thrust kick. You draw up the knee, pivot on the supporting leg, thrust the leg in a straight line to the side and pull it back, with the foot edge or heel as the contact surface. It stops an opponent who is coming at you. The prerequisite is yoko-geri-keage, the quick side snap kick.
In competition it scores by height: under the World Karate Federation (WKF) kumite rules, a kick to the trunk (chudan) earns 2 points (waza-ari), a kick to the head (jodan) 3 points (ippon) [1]. To the head it must stop in control, about 5 centimetres before the target (roughly three fingers wide) or only touch lightly [1].
Why is the kick so effective? A review of 88 studies on kicks in combat sports found the highest measured impact force for the side kick: up to 9015 newtons, roughly the weight force of about 900 kilograms. The values vary widely, from 122.6 to 9015 newtons, depending on the measuring method [2]. That means the kick can do damage, and that is why it must be controlled. Expect several weeks until the line sits (practical estimate, not a study).
You stand in fighting stance, hips turned slightly toward the target. Look over the shoulder, not at the foot. Milestone: you can stand calmly for 10 seconds without losing your balance.
The kicking leg is drawn up with the knee forward and up, the heel toward the buttocks, the foot tensed. Milestone: you hold the position for two seconds without the supporting leg wobbling.
The supporting leg turns slightly along, the knee stays over the foot and points in the same direction as the toes. The supporting leg carries the rotation. A review on kicks links a pivoted supporting-leg stance with high impact and at the same time with rotational load on the supporting knee [3]. Milestone: you pivot without the supporting knee falling inward.
The hip pushes the leg outward, the leg extends straight to the side, the foot edge or heel points to the target. The upper body leans away slightly. Milestone: five kicks in the air end at the same height and line.
The leg returns by the same path, and you set it down in control. The recoil is part of the kick. Milestone: you land calmly and can go straight into fighting stance.
In this kick the supporting leg bears the load. In a survey of 146 South African karateka, the right knee was the most frequently injured site, often through kicks [5]. The review on kicks describes that the pivoted supporting leg raises the impact but can load the knee [3]. Make sure the knee stays over the foot and never tips inward.
A measurement on Sanda fighters doing continuous side kicks (so TRANSFER from another sport) found that the kicking leg measurably tires over 30 seconds, the supporting leg hardly, and that the supporting leg relies on the interplay of calf and front shin muscle for stability [4]. Tired legs lead to mistakes faster: end the exercise before the form breaks down.
In competition, attacks to legs, joints and the instep are prohibited, as are kicks against an opponent lying on the floor [1]. Practise on pads only with an instructor, not against hard surfaces. This guide explains and motivates; it does not replace supervised training.
The kick is a thrust, not a swing: imagine pushing open a heavy door with the foot edge. If you feel the leg swinging like a pendulum, the hip is late. The hip pushes, the leg follows. The review distinguishes kicks that act like a throw from those that act like a thrust [2]. "Kekomi" means roughly "thrust in", the second kind is meant.
How to fit it into your week: practise three times a week for five minutes after the warm-up. Ten kicks per side in the air, filmed once from the front. The pad comes in only when the instructor releases it. This is practical experience, not a study.
Keage is the quick, snapping kick, kekomi the thrust kick with pressure. In kekomi the hip thrusts the leg straight out. Keage is the prerequisite for kekomi.
A kick to the trunk scores 2 points (waza-ari), one to the head 3 points (ippon) [1]. To the head it counts if it stops about 5 centimetres before the target or touches only lightly [1].
For the supporting leg it can be if the knee falls inward. The review describes rotational load on the supporting knee in a pivoted stance [3]. With warm-up, knee over foot and an instructor the risk is smaller.
Expect several weeks for a clean line in the air. This is a practical estimate, not a study. Control against a target takes considerably longer.
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