In order to develop greater power in your karate techniques, you must first master the 5 basic physical principles of power listed below. One must focus on these fundamental principles before developing any speed in your techniques.
STANCE: The Shorei style is based on strength and force. The stances are lower than other styles, which focus on speed and flexibility. The stance is the base upon which everything else is built. One must first develop a good, low stance before learning how to punch or kick. A typical Shorei stance is the Zenkutsu dachi, which should have your feet place two shoulder-widths from front to back and a shoulder and a half width left from right. The kiba dachi, or horse stance, is also commonly used in a lower position with the knees bent so they are directly over your feet, as opposed to other styles which tend to stand almost "straight-legged" in their horse stances. The premise of the lower stance is for greater power and small target when being attacked.
HIPS: To develop greater power in punches and blocks, one must learn to move their hips first followed by the punch or block. By moving the hips a fraction of a second before your technique, you will accumulate greater force through the torso leading the arms to the target. If your hips are stationary while punching and blocking, you only have the power of your arms behind the technique. If you use the torque of your whole body, through your hips, you will not only have a stronger technique, but a faster one as well.
BREATH: Breathing is the most fundamental principle of life. Without it one cannot exist. The same follows through to Karate. Anyone who has taken a basic Karate class will know that you inhale fully and deeply before a technique, and exhale completely with a sharp focus at the moment of impact. Have you ever tried breathing in while punching or blocking? Needless to say, it doesn't work very well. Not only does it restrict your movement by bringing air into your lungs, causing them to expand while moving, but it also leaves you vulnerable should someone strike you in the diaphragm area. By properly exhaling during a strike your are constricting your lungs, thereby causing more power with a wider range of movement capability. You are controlling the adrenaline built up in your body to be released with greater exertion while exhaling, versus keeping it pent up inside during inhalation. And lastly, one of the most important principles of the exhalation during strike is to KIAI. This loud, audible response not only focuses all derived from the above physical principles at one point in time, but it also will "scare the heck" out of your opponent. People typically do not like loud noises and the natural reaction would be to shy away from such. The Kiai works great for distracting, unnerving, and causing your opponent to lose their focus.
ACTION-REACTION: One of the most basic laws of Physics - for every action there is an equal reaction. Everyone is taught from the first class that whenever you punch, you pull the other arm back into "empi position". One thing we practice in our classes is called "empi strikes" - which means striking with your elbow to an imaginary target behind you. The reason we practice this is to not only use it in case of someone approaching from behind with a "bear hug" or other similar locking technique, but by practicing empi strikes you are actually improving your forward seikan strikes. The great force that you pull your empi backwards, the greater the force you will have forward momentum for a lunge punch.
MIND: Your mind is the last principle of power. It is often said one should have a mind like calm water, one that reflects and is mindful of everything around it. If you allow something to disturb your mind, you lose focus and develop a rippling or wave effect that disrupts concentration and limits your ability to respond quickly and accurately. When practicing karate, always maintain a clear, focused mind on the present task and surroundings. Train your mind to keep from wandering to the past or future. Keep it from thinking of other things that you need to do or accomplish. If you always practice karate with the utmost seriousness and clarity of mind, you will be better prepared to focus during a time when you may actually need to use a technique.