Zhan Zhuang

The originator of a martial arts called Yiquan which bases itself on Zhan Zhuang wrote this article outlining the practice and therapeutic potential:

"Zhan Zhuang exercises
Written by Wang Xiangzhai in late 1950s or early 1960sTranslated from Chinese by Andrzej Kalisz in 2004"

http://www.yiquan.academy/articles.php?article_id=42

A reference on the Wikipedia article states:

"Those unfamiliar with Zhan Zhuang can experience severe muscle fatigue and subsequent trembling at first. Later, once sufficient stamina and strength have been developed, the practitioner can use Zhan zhuang to work on developing the sensation of "opposing forces," as well as one's central equilibrium and sensitivity to specific areas of tension in the body" (https://en.wikipedia.org/wiki/Zhan_zhuang).

I cross-referenced this claim elsewhere (The translated Wang Xiangzhai article mentions sensations that go away but doesn't make it seem like anything "severe") and found problems can potentially occur when practicing for long periods of time or from being in the incorrect posture.

Others say this is one of the best practices anyone can do without needing a teacher. 

Much of the practice involves a mental component directed toward the body and getting into the habit of allowing oneself to relax physically.

I found this video helpful in understanding the basic Cheng Bao posture:

https://www.youtube.com/watch?v=j_rgN4wZj7U