Learn ap kubi in taekwondo: the long front stance with a bent front leg. With milestones, mistakes, knee protection and notes on poomsae scoring.
The honest answer: ap kubi is the long stance with a bent front leg and straight back leg, and it is the base of almost every taekwondo form. The front knee stands over the foot, the back leg is fully extended, the upper body stays upright. If you master it, you move more calmly and stably in forms.
In competition, stances count. The World Taekwondo poomsae rules name the ap gubi (WT's spelling) explicitly as an example: stances and hand movements are scored for accuracy, and each small mistake costs a 0.1-point deduction [1]. Accuracy accounts for 4.0 of the 10.0 points [1]. A clean stance is therefore real money in scoring.
Realistically you need a few weeks until the stance sits stably and months until it flows inside the form (experience, not a study). This guide does not replace supervised training.
The difference between a good and a bad ap kubi often shows only on video: if you let the knees fall inward or twist the hips sideways here, you build that mistake into every form later. It pays to learn the stance early and thoroughly instead of picking it up on the side.
Stand upright in ap seogi, eyes forward. Milestone: you stand 20 seconds calmly without swaying.
Place the front leg forward, the length is about one and a half shoulder widths, the inner edges of the feet stay on a shoulder-width track (practice standard). Milestone: both feet point forward, neither turns outward.
Bend the front knee until it stands over the foot, but no further. The back leg stays straight, heel on the floor. Milestone: from the side you see a straight line from the back leg to the back.
The hips point in the direction of the step, not sideways. The torso stays upright, the head faces forward. Milestone: a partner can lay a stick across your hips and it points forward.
Change feet in flow: step, hold the stance for three seconds, next step. Milestone: ten stances in a row without the knee collapsing inward.
The stance stresses the knees, especially with long practice. A measurement of 157 Korean taekwondo athletes found that leg alignment differs by discipline: poomsae athletes showed more inward-pointing knees (genu valgum) at the dominant leg than sparring athletes [3]. That is a cross-sectional study and proves no cause, but it shows why knee tracking matters in forms.
A motion analysis also found that poomsae practitioners sway more while kicking than sparring athletes [2]. If you want to stand cleanly in forms, train balance.
Do not practise if your knee hurts. Do not start with deep stances; increase depth slowly. Knee pain is a reason to ask your coach. This guide does not replace supervised training.
Avoid fast changes between deep stances at the beginning. Count calmly: step, stance, hold three seconds. When tired, the knee tracking goes first, so take a break rather than keep practising (practice standard).
Stand with your back foot against a wall and push it into the wall. You feel immediately whether the back leg is really working. If you only drag it along, you notice the strength is missing. This is a practice drill without a study behind it, but it shows you without a partner whether the stance holds.
Ap kubi is the front stance in taekwondo: a long stance with a bent front leg, straight back leg and upright torso. It is the base of almost all forms. The rule book spells it ap gubi.
As a practice standard about one and a half shoulder widths long and shoulder width in track. That varies by school; your coach sets the measurement.
Yes. In the WT poomsae rules, stances such as ap gubi are scored for accuracy; small mistakes cost 0.1 point [1].
The stance resembles zenkutsu-dachi, but length, posture and details differ by style. Do not simply take measurements from karate.
As a rule of thumb a few weeks of short sessions until you hold the stance without a mirror. Then punches and blocks follow. There is no study on this.
Jireugi in Taekwondo: The Straight Punch With Hip and Breath