Lectures on the Sūtra of the Collection of the Father and Son (Pitāputrasamāgamanasūtra) (46)

The wind inside the body may move from the lower part of the body upward, or from the upper part downward, or from left to right, or from right to left—this is the mobility of wind. When we sit in meditation, we can perceive it; as soon as the Qi meridians move, we can feel it. The Qi meridians are wind; wherever the Qi meridians reach, a bodily sensation arises there. Originally, when you sit, your body is slightly bent; but once the Qi meridians run to the back of the body, your back immediately straightens up. You don't need to deliberately sit upright—the body straightens naturally on its own. This is the mobility of wind and its governing effect on the body.