Zhang thinks human life consists of body(形) and Shen(神 spirit). Body comes from Jing(精), Shen comes from Qi(氣). The common basic of body and Shen is Qi. Thus the elements of human life are Jing, Qi and Shen. Among the three life elements, Jing is the lowest level. To preserve Jing is the key to Life Care. To preserve Jing, we should rest body and Shen, and Shen rules body, so to rest Shen is necessary to preserve Jing. When Jing is full, it converts to Qi, and Qi converts to Shen. Shen is ruled by mind(心), so mind sould be quiet. There is a gate through which Jing and Qi pass. It is called Mingmen(命門), and it sould be closed tight to preserve Jing.