What Moves First?
To punch or kick with power, the arm or leg must first be chambered, or cocked. Otherwise, the hand or foot is just being moved toward the target, it is not being thrust at the target with the mass of body behind it. If our fighting stance is with the arms hanging downward, then to punch with any power, the elbow must move first so it may give some chamber to the arm before the punch. However, since any good fighter fights with the hands held up in a guard position, the arm is already is cambered, so the first thing to move in a hand attack is the hand, with the elbow and body moving behind it. Since we cannot float, while we are in a fighting stance our legs are always hanging below the body. Therefore, the first thing to move in a kick is the knee, so it may give chamber to the leg before the kick. Otherwise, it is just a kick. A non chambered kick may score a point in a tournament, but it will never do any serious damage to an attacker.
Power versus Speed
If you attack with power, you will be slow and most of time the opponent will move out of the way. If you attack with speed, the opponent may not see it coming and may get hit; maybe not with as much power as with a power attack, but at least the opponent gets hit; whereas, with the power attack, the opponent usually does not get hit at all. If you are good with fakes and feigns and at reading your opponent's actions and reactions, you can set up combinations that cause the opponent to move away from one attack and into another attack, The combination of your speed and the opponent moving into the attack means that the opponent will get hit with power. So, to hit your opponent with power, attack with speed, not power.