Because in Chinese medicine, the human body is yang, the lower part is yin, the latter part is yang and the first part is yin. Everything conforms to the law that Yin turns to Yang, and all problems of Yin will be reflected through Yang. For example, when a person has a fever or fatigue, scratching his back will relieve the symptoms. Also, when a person is angry, he usually passes through his face, which embodies the law of yin to yang. Therefore, nourishing yang is the first step of health preservation. For example, you can point to acupoints such as Zhigou, Zusanli and Quchi.

You can also learn something more specific on the website of Zhixiutang.