Some measures for striking:
If you can reach the attacker with your outstretched foot, you should run away.You must be able to strike through the attacker. Striking his outer surface will do little or nothing. When you strike the chest, you have to aim through to the back. That is why you must be pretty close to strike. You are not aiming at the front -- you are aiming at the back.
If you can reach the attacker with your outstretched fist, you should kick.
If you can reach the attacker with your outstretched elbow, you should punch.
If you can reach the attacker with your shoulder, you should strike with your elbow.
When you are extremely close, it helps to know how to grapple.
My Sensei explained to me that when you punch, you should have the feeling (or idea) of crashing your body into the attacker's. Another way to express this is to say that you punch (or strike) with your body, not your arm.
Most people do not practice crashing into each other. This is much like taking hard falls in Judo or Aikido.
Charles C. Goodin