Within Goshin-Jutsu, Sanchin dachi is sometimes called a small hourglass stance or immovable stance (which is discouraged, to avoid confusion with ready stance) Sanchin dachi literally translates as “three battles stance”, but that’s neither relevant nor important; sanchin dachi earned its name simply because it is the main stance used in the kata Sanchin.
Karateka use frequently use sanchin dachi in dynamic tension exercises, and to provide an extra degree of stability when fighting in the clinch. Some karate styles, like Isshin-ryū, use sanchin dachi exclusively. Goshin-Jutsu mostly uses sanchin dachi as a transitional stance to quickly turn around, like a hook stance, except you are stepping in front of yourself, instead of behind yourself.
To enter a sanchin dachi, your rear foot must be about two shoulder-widths behind the front foot, and one shoulder-width to the side of it. The bodyweight evenly distributed between both legs, like a fighting stance. Your knees and toes are pointed inward. The legs can (and should) be tensed to a greater than normal degree in this position, leading to its popularity as a leg exercise. It is imperative to focus on your posture in this position; make sure your chin is back, your spine is straight and elongated, and your backside is lowered, as though you were resting on the edge of a barstool.
[photo of sanchin stance from the front and side.]
If your legs feel comfortable, then something is wrong. Your leg muscles should experience a feeling of burning and tension, more so than with others stances. This cultivates tremendous leg strength, which will power all of our techniques. In order to keep and maintain this burn, you must lower your center of mass, and keep it low. Again, a good stance is 2” (5 cm) lower than what intuitively feels like a good stance.