Kao (pronounced Coww) is the often over looked and under appreciated principle in two popular Chinese Martial Art styles - Mantis Boxing (Tang Lang Quan), and Supreme Ultimate Boxing (Tai Ji Quan). Kao is defined in both Tai Chi's - 13 Principles, as well as the Praying Mantis Boxing's - 12 Keywords - the hard and fast tenets of these styles.
Kao 靠 translates as 'lean', or more specifically 'lean against; depend on'. In Tai Chi circles it is often referred to as Shoulder Stroke which I'll explain later. When reviewing the old texts, you can see the character for Kao is exactly the same in both styles. This is significant given that both styles are rooted, and revolve around stand-up grappling.
As mentioned, in Tai Chi, Kao translates as 'Shoulder Stroke' or 'Lean' for some. In Mantis Boxing, Kao is translated as Lean. It is actually both. Stroking with the shoulder, or leaning to effect a take down. Stroking can be explained as the physics term - Applied Force, or in some regards Normal Force.
How can stroking with your shoulder, or 'leaning' be a major principle in a style? Sounds a bit silly right? I remember thinking so myself at one time. "What is the point of that?", I said to myself many years ago while reading book after book searching for answers.
At the time I was researching these principles, I was primarily a striker. I did not have a ton of grappling experience, so this idea/concept was foreign to me. Having delved into the grappling world since then, much of this makes more sense and has become 'obvious'.
I now espouse that if you give a Tai Chi manual to boxer, they won't have a clue what to make of it. If you give it to a wrestler/grappler, chances are they will immediately decipher the terminology, and understand the content enclosed.
Note: I use Tai Chi as a reference here because it is the most heavily documented and widely proliferated of all the Chinese Martial Arts. Lucky for us, Mantis Boxing (Tang Lang Quan), and Supreme Ultimate Boxing (Tai Ji Quan) are 'brothers-in-arms'. Heralding from the same region and time period, with many shared principles.
Back to the 'Shoulder Stroke'...it's not like we are stroking our cat. On the one hand if we tried to pull off a shoulder stroke at long to mid range with our opponents hands ready to maul us, then yes, we would be punished severely for this transgression.
Additionally, if we are in striking/kicking range and leaning forward, we are giving our opponent a significant reach/range advantage. One we will pay the price for before we ever get close enough to grapple (Lǒu 摟).
On the other hand, if we are in close range, where Tai Chi and Mantis Boxing heavily function, the game changes. When our opponent is controlling our arms, or body (neck hooks, underhooks, body clinch), or our arms are occupied controlling theirs, then there are certain limitations on what can and cannot take place. This is where Kao becomes increasingly valuable.
Here you can see an application of Kao being used to escape a tight body clinch.
Once we are engaged in the Grapple (Lǒu 摟), we now start to lean in to protect our position. If we continue to stay upright, then we are susceptible to Crashing Tide (single/double leg takedowns), Step Up to Seven Star (body clinch with leg hook), Point at Star (standing arm triangle with takedown), Reaping Leg Throw, etc.
The shoulder stroke terminology, is a good way to explain the use of the shoulder in some of the takedowns shown above, and in this video below. As you can see, the shoulder is used heavily to affect applied force in the execution of the takedown.
These are a few of the manifestations of Kao that show its potential. Clearly the founders of these two styles of martial arts realized the importance of this principle and rightfully placed it in the list of tenets to be passed down from generation to generation. When properly understood and used, Kao can be a valuable tool when playing Supreme Ultimate Boxing or Praying Mantis Boxing.
So 'Go Lean' and topple your foes!
Edited and revised - 1/4/18.