The hardness and the sharpness of the elbow make this attack devastating.The rotation of the hip is what gives the strike its power.
Krav Maga techniques
When you start practicing Krav Maga for the first time, you start by learning the roots of Krav Maga techniques. You basically follow your instructor teachings. Thus, you are usually greatly influenced by your master experience. Once you've learn to master them, these basics are developped in more difficult techniques. To reach this point, you must practice a few years. And when you approach the black belt, practitioners starts questionning themselves. They acquired sufficient experience and knowledge to judge what they know and what they can do. This is a tipping point where your Krav Maga style begins to express itself.
You'll feel the need to expand your knowledge about Krav Maga techniques. Watch Krav Maga videos, compare your techniques with the other federations. If you can, try other martial arts. You have to stay open minded to improve your technique.