Introduction to Koshi
The word koshi is simply the Japanese word for the area from your navel to your hip sockets, but when discussing martial arts it specifically refers to how to generate power with your hips, and it is used in place of the longer, more accurate phrases koshi hineri/koshi wo hineru (hip twisting) and koshi kekomi/koshi wo kekomi (hip thrusting). The idea of utilizing the hips to generate power through twisting motions or thrusting motions is found in nearly all striking arts in some way, and it is vital to both power and speed because of how your body is connected to the hips.
The hips are self-stabilizing thanks to the independent actions of the legs and the pivoting and tilting action of the spine, which likely developed in the way that they did in order to support our center of gravity as efficiently as possible. This structure means that all unified body motion must transfer through the hips. Motion from the legs transfers to the hips, and motion from the upper body transfers to the waist. If you think about all of the movements that you do in a day, you will realize that most of them are performed by your head, arms and legs while the area between your waist and hip sockets remains relatively still. In order to move your koshi, you must drive your body with your legs, and if you do this then your upper body will tend to move in conjunction with the hips. This is the basic idea that koshi, as a method of power generation, relies upon.
The first method generally used to develop power by using the hips is to twist them. In order to force the hips to twist, which will cause the upper body to follow unless the practitioner is consciously holding the shoulders in place, there must be unidirectional drive provided by one leg, or oppositional drive provided by both legs. If a person stands in a fighting stance, they will most likely have one foot behind them and one foot in front of them, to some degree. If they push forward with their rear leg, it will cause the attached hip to drive forward, twisting the body–this is unidirectional drive provided by one leg. If they push forward with their rear leg and push backward with their lead leg, then they are forcing their hips to twist in opposite directions to twist the body–this is oppositional drive provided by both legs. Both methods allow the upper body to remain relaxed (for speed) and still throw the entire weight of the body (for power) behind a strike.
The second method that is typically used to develop power by using the hips is to thrust or drive with them. This method is different from the twisting method in that the hips move in the same direction rather than one remaining stationary while the other moves or both moving in opposite directions. In order to do this, both legs must drive in the same direction and this is usually accomplished through unified muscular contraction of the abdominal and gluteal muscles more than a pushing action from the feet. Hip thrust can be utilized by itself to generate power, particularly when kicking or striking with both hands at the same time, but it is most effective when used in conjunction with hip twisting.
Experienced karate practitioners will sometimes refer to “internalizing” koshi, or using the tanden (the Japanese pronunciation of the Chinese tan tien, referring to the center of a person’s energy) to generate power while barely moving the hips. This is generally explained as shrinking the movements of koshi or using ki/chi/qi, depending on who is explaining it, in order to provide a technique with the most power possible as efficiently as possible. This concept seems impossible when you see the amount of movement that is evident when a karate practitioner first starts to develop koshi, but it is based on the fact that a person’s body can only reach a certain speed (this will be different for every person) and so reaching that speed in a shorter distance will result in less movement and less energy used without sacrificing speed.
Those who are capable of striking with speed (and, therefore, power) despite minimal movement of the hips have become so in-tune with their bodies, and the use of koshi has become so second nature to them, that they have found the smallest amount of movement and muscle contraction and timing to accomplish with a flick of the hips the same speed that takes a full hip twist for less experienced practitioners to reach. The process of combining hip twist and hip thrust and making them as efficient as possible can take a lifetime, but it is a very physical representation of the idea that martial artists should constantly seek to improve themselves.