This stance (also commonly called a Hard Bow Stance) is a mid-level stance that places one leg forward of the other. The feet are spread at least shoulder-width apart (usually wider, up to a 45° alignment on the Octagon). The front leg is bent and the back leg is straight (often rigidly straight). Both heels must remain on the floor for maximum rigidity. The hips and shoulders should turn to face local octagon angle 1 and this is what necessitates a wide stance width. Ideally, the hips and shoulders should be aligned on the local 3 and 4 octagon angles. The front foot is generally facing forward, and the back foot either faces forward or about 30° off to the side.
To adopt this stance either move your front foot to local octagon angle five or move your back foot to local octagon angle six. The toes of both feet should now rest along an imaginary line stretching between local octagon angles five and six (on the octagon angles five-six axis). This allows your Center Line to be focused directly toward local octagon angle one. Weight should be equally distributed along the bottoms of both feet. If you feel more weight on your front foot then shift your torso and hips back to better equalize your weight distribution.
Care must be taken when bending the front leg to not let the knee go forward of the ankle position. Doing so puts greater stress on the knee joint and can lead to damage to the ligaments, tendons, or muscles of the knee. The shin should be in a generally vertical orientation but should be pressed forward more than 90° from the floor.
This is a very rigid and strong stance when focused toward octagon angel one and is often used to deliver back hand strikes. It is also useful in some cases for thwarting pushes or pulls or for aiding in your delivery of these same actions. This stance is quite effective at maintaining stability on the octagon angles one-two axis.
The stance is not particularly effective at resisting pressures (bumps, pushes, pulls, etc.) coming from an angle other than angles one or two. In the picture above a push coming from the direction of local octagon angle seven would set the practitioner onto his or his heels causing the stance to fail. Pressures from other angles cause somewhat different but similarly disruptive effects.
Practice this stance at low, medium, and high elevations so that any elevation within this range can be quickly adopted as required. Just do not violate the knee positioning rule when doing lower level stances.
A separate but related stance is the Seisan Dachi. This is a shortened version of Zenkutsu Dachi. The back leg is extended only a short distance back. This allows the torso to easily remain erect and the stance can often be established in a shorter period of time. Seisan Dachi is most useful as a transitional stance or when you need a momentary stance that can function to resist a push or pressure applied from the direction of local angle 1. You might think of applying this since by stepping back into a relatively deep Ura Neko Ashi Dachi, then pressing the heel of your back foot down and into the floor. This is quick and affords you with the ability to resist pressing movements or deliver a sound checking motion. You could also establish this stance by stepping slightly forward with either leg or by pulling the back leg forward when already in Zenkutsu Dachi. This latter movement is found in some Kata.