I’ve come across two things worth noting about this all-important (but little known, it seems) aspect of taiji, or IMA in general. Here they are.

An excellent bit of advice about sinking the kua can be found here. The following is a quote from that page:

The most basic requirement for doing Tai Chi is song kua, or relax the hips, means that the muscles surrounding the hip joint, i.e. where the thigh bone meets the hip, should not be used to any great degree in supporting your structure. These hip muscles can then be used to adjust the angle of your pelvis so that your upper body can remain relaxed, or direct the jin if so required. If you haven’t achieved a song kua, then everything else is academic. You will not be able meet the requirements for the rest of your body.

In Chen village the term kua is sometimes used to mean the hip joint in general. However the term song kua means that the interguinal crease is bent. The problem is that Tai Chi also requires you to bend your knees. This semi squatting position puts a lot of load on your quads (i.e. the thigh muscles on the front of your leg). Your quads consist of a group of 4 muscles. The bottom of these muscles are connected to the knee cap. The top of 3 of them are connected to the thigh bone. However the top of one of them is connected to the pelvis itself and is classed as a hip flexor.

If you engage a hip flexor, then you are using a hip muscle, therefore violating the requirement to relax the hips. So not only does Tai Chi want you to put a huge stress on your quads, it also only allows you to use 3/4 of the muscles available! This is why standing meditation is so painful, and why you can tell whether someone has begun to achieve some gongfu in their Tai Chi by just looking at how their leg muscles are developed. So what is so bad about using a hip flexor? A hip flexor is a muscle that you use pull your knee towards your chest. Now if you engage a hip flexor in a Tai Chi stance, it will pull the front of your hip downwards, thus making your bum stick out and your lower back arch. To counter this, you will have to engage muscles opposing it, i.e. hip extensors such as you gluts. Now you are locking up your hip joints even more. How can you manipulate your hip if it is so locked up?

The second piece of advice comes from Charles over at EF. Charles practices the “practical” frame of Chen style. Here’s what he had to say in this thread:

“Sit down hip.”

The use of the hip (kua) is basic to the style. I’ll use a typical bow stance, left foot forward/weighted, for illustration. In this bow stance, the rear (right) hip should be sunk and open and the rear leg not completely straightened (i.e. knee not locked). (In Chen style, the rear foot often angles outward more than 45 degrees, often as much as 90, which facilitates sinking the rear hip in lower stances.)

The hips do not generally face directly forward (”squared”) in the bow stance, but, rather, 20 or 30 degrees to the right. With exceptions, squaring the hips with the front leg causes excessive tension/stiffness in the rear leg and lower back, separating the upper body from the lower body/ground, closes the rear kua (inguinal crease) and prevents sinking of the qi.

From the bow stance, if you shift your weight to the rear (right) leg, the left inguinal crease opens as the torso rotates away from the front leg (to the right), closing the right inguinal crease. (Closing the inguinal crease causes your pants to crease; opening it, the crease goes away.) Think of Yang style “roll back”, but on the opposite side.

The opening of the left inguinal crease maintains the alignment of the left hip, knee and ankle. If the left crease is not opened, the knee is dragged along with the retreating hip/torso while the foot/ankle remains in place. Doing so causes the knee to bend sideways (or attempt to), which it cannot effectively do.

As the weight sifts forward to the left leg, the torso rotates towards the left, closing the front inguinal crease and opening the rear (right) crease. As it does so, the right leg spirals inward - the knee rotates towards the left in concert with the turning of the torso, hip and ankle - and the left leg spirals outward (toward the left). Ni (outward) and Shun (inward) reeling of silk. The ankles, knees and hips work together: when one part moves the whole body moves. This is chan si jin, or at least a piece of the puzzle regarding coordinating the joints of the lower body.

I would encourage everyone to follow the advice listed above and try to work this into their IMA practice. This is a significant piece of the puzzle. If you can get this, then you will find many other IMA abilities are opened up to you. Things like peng jing, relaxation, etc. naturally flow from song kua. If you don’t have this, then your development will forever be stuck at a low level and you may waste years of practice time.

Yes, this is that important.