The side kick is perhaps the most important kick to master, and it takes much repetition to understand its place in combat. In this study we can see how subtle changes in body movement lends power to the kick; where a decision must be made between speed and power based on chamber. Body movement, timing, and various foot positions help overcome a less committed chamber and assist speed of delivery. And as #brucelee pointed out, speed has much to do with power! Furthermore control of power and foot angles gives the fighter greater ability to decide between levels of response for a given threat. This kick can be a lethal technique or simply break a few ribs, or just shock the diaphragm. Glancing, direct, snapping, penetrating blows all have their place.