This small book "Wuji Style Breathing Exercise" contains what I believe to be one of the most profound, and yet one of the most obscure esoteric practices known to man. In it is the only English explanation of the Taoist version of this practice of which I'm aware. I ran across it in 1996, in my search for an understanding of the inner workings of tai chi. Since that time, I've practiced the method very seriously although with varying degree of diligence. Its practice was very instrumental in my development of the Coherent Breathing method, circa 2000, which dramatically enhances the effect of Wuji Qi Gong, as well as other forms of Qi Gong.
The authorship is also something of a mystery. The translater, a Mr. Men Den, explains that he is the student and ghost writer for the well known Tai Chi master, Cai San Fong. However, other reports, purportedly by those including Cai himself refute this. The author, whoever it is, describes that the wuji breathing method was handed down from a direct student of Yang Cheng Fu, it being the esoteric basis of Yang family taijiquan (tai chi).
The reason for all this mystery is that between the covers of this odd little book is (based on my humble opinion) the essential core practice of Taoism. There are equivalent (also largely obscure) yogic practices in Hinduism and Kashmiri Shaivism, which I will bring to your attention a bit later.
If you've studied Taoist philosophy, you'll recognize the term "wuji". In Taoist cosmology wuji refers to the "primordial undifferentiated". Taoism concerns itself with the "process" or mechanics by which differentiation and non-differentiation occur, yielding "taiji", dynamic differentiation of yin and yang, and its ultimate result, the dissolution back into wuji. You may have heard the phase "taiji comes from wuji", and its complement, "taiji returns to wuji".
Very importantly, this "process" refers to the "energetic" evolution of the physical universe, the "cosmos", and to us (humans), as micro-cosms of the macro-cosm. As such, it is through the practice of "Wuji Breathing" that one facilitates this process and realizes the essential Taoist experience of both "wuji" and "taiji".
Tangible benefits include increased vitality, balance, energy, intuition, strength, power, endurance, and wellness. Esoteric effects include, among other things, a "profound energetic capacity" for healing, martial arts, etc. and a very clear and evolving sense of "oneness" with the cosmos.
It is best practiced in a standing position 20 minutes per day, in combination with Coherent Breathing.