Consider the crescent kick. When executed with a degree of élan it can be a whirling example of physical freedom and self-control. Some people throw crescents so open and limber they appear to momentarily execute the splits while standing up. 
After all it’s such a beautiful kick that dancers perform it as part of their basic skill set from Beijing to Vegas. Like the giant wagon wheel it resembles, it just keeps on rolling along.
That’s the problem.
The crescent kick lives a split existence because it really has two versions which should be completely disassociated from one another.
There is a correct and perfectly acceptable way of throwing the kick which should be reserved for dancers. There is also a martial arts version with a very different shape to it. And the difference should be noted.
At the end of China’s last dynasty, especially after the take over by the Manchus and the intrusion of the foreign powers, many martial experts hid out like fugitives among the ranks of Chinese opera casts. Also, they needed to fill their rice bowls and students had become scarce once the gun entered Chinese life. Few people wanted to work hard and labor long when a bullet could neutralize all their skill. So teachers found work as choreographers. They taught in what most westerners would think of as a “variety show”: namely, the energetic and often gymnastic Chinese opera. Of course these teachers made concessions for entertainment reasons and did not stress the creation of power or the requirements of purpose.
If this seems strange you have to consider that even a major martial artist, such as Adam Hsu, is a choreographer for one of Taiwan’s top dance troops. That’s not to mention all the aerobic-fitness classes where the authentic martial teacher is basically making a living by conducting dance classes. There’s nothing wrong with this, actually. The trouble begins when categories get clumped together. For instance, many students from the old opera system went out and taught martial arts. Why? You ask. Because the opera also fell on hard times. Look at Jackie Chan’s career. If the southern branch of Beijing opera he trained in as a youth had survived he would hardly be an international star now. He started out to become a humble opera performer and defaulted to an international Kung Fu entertainer.
With all this background we can now examine the crescent kick and, simultaneously, get a good lesson on the importance of knowing history. A good example starts with the shape of the leg itself. No, you don’t really strike with the leg fully extended like a pole. The resulting impact would be destructive to the joints of the knee, no matter the area of contact. The leg should be bent a little. The ten degree insertion of ligament in a bone requires a bend in the limb to engage the muscles and provide the necessary shock absorption. If you know you are going to hit a stationary target you might get away with this but that’s more of an argument for moving target practice than locked legs.
The next error is going to make a few people unhappy because it diminishes the pretty effect. When a proper crescent kick is thrown the back should be hunched slightly and definitely not straight. This is a dance kick, back straight and even arched—not a martial kick which requires the back muscles and psoas to be engaged throughout the kick.
I remember an incident I saw in China where a young American was demonstrating Tai Chi. He was lucky enough to have a member of the Chen family, who was also a national judge, as his mentor. After handing in a good performance he was almost accosted by a different coach who came up to him and wanted to give him a tip. She probably figured what she was going to say would match his six foot plus frame and make his kick more exciting, so she explained how to stand straight up during a crescent kick. Within three seconds the Chen coach has rushed across the room and was telling off the WuShu coach and, basically, saying don’t feed that stuff to my student. She was right to do what she did and to keep these versions clear. Do either, but don’t confuse a straight backed dance move with a martial kick.
The next problem centers on the hip joint itself. If you want some problems like I have in my right hip just keep spinning from the joint at full extension. This of course has something to do with the above problem of back engagement but it has some other factors, too. Imagine the actual fighting range of the kick. If you are looking at a spot on the wall the power range of the kick will be about forty-five degrees to either side of the spot. You may be limber enough to throw your leg far past the moment of impact but all it will really do is hyper-extend your kick and distort the range of your hip. What SHOULD happen is that the moment you reach the fort-five point beyond the medial line you should bend the knee and bring the kick in with a crane stance rather than just keep flinging out the leg as far as it goes. I you hear a big “click” in the hip it may already be too late.
So here are the so-called “mistakes”: reiterated;
A slight bend to the leg.
Back hunched, not straight.
Circle the kick but retract it when just past the focus point, don’t “fling”.
That’s a lot. This is really important because the force generated by a good martial kicker is enough, especially in the somewhat more restricted western body type for instance, to eventually damage the hip joint itself. I know a number of people whose hip replacements are at less partially attributable to their martial habits.
There is a fourth consideration that is more general. The crescent kick itself is relatively useless as it is taught. It is what might be termed a “generic” kick. It opens the hips joint, teaches a very important method of generating power and creates a general action which can be varied for all sorts of other effects.
For example, the crescent kick with the arch or outside of the foot is a classic blocking technique often associated with fighting someone armed with a knife.
The famous Ax Kick is a variation of a crescent that stops halfway through its arch (when it touches the hand, in practice) then falls straight down to strike with the heel bone.
On the ground the crescent instantly transforms into a sweeping action of the leg.
On your back the crescents become the famous “ground flower” kick of Kung Fu.
All these variations just begin to show how important the crescent can be. But, as in all these ancient and well constructed movements, the obvious and the hidden are neighbors. A “no pain, no gain” philosophy isn’t half so helpful as the wiser version: “No brain, no gain”.
