The vertical line running from the top of your head to your tailbone enables you to turn easily provided the vertical line is configured properly.

In the Commencement Movement the first part of the vertical line configuration is at the neck. In Grandmaster Wei Shuren’s book on the 22-form it is said that we should touch the back of our neck to the collar.

When you do this your chin will come closer to your neck as if tucking the chin in. As this occurs you will find that the back of your neck moving to the collar (assuming you are wearing something with a collar).

The second part of the vertical line configuration begins as soon as the neck configuration ends. This is when you open up your chest by imagining that there is a stone sitting on top of your chest.

The weight of the stone causes your chest to open up like two doors separating, allowing the stone to descend to your tailbone.

As the stone descends it will pass by your lower back. This is where you fill out your lower back, thus aligning the third part of the vertical line.

A quick way to check if you are doing this properly is by placing your back against a wall to check if there is a gap between your lower back and the wall. If there is then you are committing the error of protruding the buttocks.