kendo-guide | Shizentai means "natural posture". However, it is not your ordinary posture.
You must learn the natural posture in order to stand naturally. Yes. Very complicated but you will get used to the posture.
The key point are;
to straighten the back of your neck, to pull your chin in, to tighten the butt cheeks.
It does not sound like a natural posture. Very uncomfortable for the first time you try.
Probably you know there is a difference between being relaxing and being lazy.
We do not want to be lazy. We need an effort to keep your posture but you can be relax.
That is what we want. Ok, this is how we create this natural posture.