Background
In TCM, yáng xū describes a state where the body's warming, activating, and transforming force is running low. If qi deficiency is "not enough fuel," yang deficiency is "the furnace won't hold a flame" — not just low energy, but a pervasive sense of cold, especially in the lower body and extremities, along with a tendency toward fluid that should be warming and moving instead pooling or leaking. Jingui Shenqi Wan is the canonical kidney-yang formula; Fuzi Lizhong Wan warms the middle burner (spleen-kidney axis). Both address cold, but from different anatomical and functional angles — one from the "root fire" at the lower burner, the other from the "digestive fire" at the middle. This tag helps a reader see why they share a page despite targeting different concerns.