A little while back I saw a posting on Kai-He on a Tai Chi group in FB. While it’s an interesting attempt to explain KH I could not help but feel that they are off the mark.
Kai-He or Open-Close is a training principle in Tai Chi. Though you can say that all styles of Tai Chi have it, however, it is best encapsulated by the Wu-Hao style, hence the version of Wu style form in Dong style Tai Chi is also known as Kai He because this training principle runs like a thread through the entire form.
IMO a principle like Kai-He cannot be grasped easily without mastering the 5 points movement principle. This is because we can think of Kai-He as an extension of the 5 points principle. In TaijiKinesis, we don’t have to keep adding more and more to the art. Instead, we just need to have a few key principles which can flexibly translate into different things. Then we can master more by learning less.
Kai-He is training to actualize the principle of using the body as a bow. The body has 5 conceptual bows. Thus, Kai-He provides the training for accessing the 5 bows and not just opening and closing the arms as commonly seen when practitioners go through this form.
A powerful bow has high tensile strength and difficult to bend. Hence, when playing the form we exhibit minimal outer movements in tandem with the principle of a strong relatively inflexible bow.
When applying the bow principle in push hands we have to adhere rigorously to it. This is why your training partner will find himself launched backwards strongly, suddenly and quickly despite seeing little movement on your part.
I am just giving a simple explanation of what Kai-He is about here. The actual principle is a bit more complex. Many of the keys to making Kai-He work are also found in the Yang style long form. Hence, do not disregard its training.