Wu Jianquan of Wu style Tai Chi demonstrating how to centre the coccyx perfectly.
People often get very confused about “tucking the tailbone” in Tai Chi Chuan. It’s a posture requirement that’s mentioned in the Song of the 13 Postures, where it says:
“When the tailbone is centered and straight,
the shen [spirit of vitality] goes through to the headtop.”
The tailbone is what’s more normally known as the coccyx. Notice, there’s no mention of “tucking” here at all, just keeping it centered and straight, which makes me wonder where everybody gets the idea of tucking it from? It’s quite a crucial misunderstanding because the word “tucking” implies bending the hips and tucking under, which results in an unnatural and distorted posture that isn’t comfortable at all. You can’t even stand comfortably like that, let alone fight!
I find that the best way to achieve a centered coccyx is to first bend the knees (you can’t ‘centre’ you coccyx with straight legs) and then relax the lumbar region of your spine. You’re looking for a natural feeling of lengthening. A dropping down. Once you’ve got that feeling then your coccyx will be in the right place. You shouldn’t feel any of the muscles or tendons in the backs of your legs being activated when you do this either, so look out for introducing tension there – it’s usually a sign that you’re starting to “tuck”, rather than lengthen the spine.