The kidney yang is often referred to as the source of fire in the body. It is associated with dynamic activities of the body from the metabolism of foods to sexual vitality. Because of the warming quality of yang a a deficiency in this area manifests with signs of coldness. Cold hands and feet, especially at night along with a tendency to be cold or a sensitivity to cold indicate some weakness here. Often there will be chronic low back pain and/ or knee pain as well. Frequent nighttime urination or especially pale urination are further indications of a yang deficiency. Menstrual irregularities such as low back pain with flow, spotting before the flow and an inadequate rise in the basal body temperature are further indications of a yang deficiency. The yang warms the uterus preparing the way for implantation of the embryo. Yang tonics in the form of foods, herbs, and drugs must be employed judiciously to avoid burning up the bodies yin and fluids.