When executing kicks in full contact matches, you have to develop your timing, distancing, and accuracy. When throwing low kicks, you want to get your opponent moving back or counter his attack. The goal is to limit his ability to defend your kicks. In the video below (from 2002 Shidokan Team USA which aired on ESPN) you will see feints to set up low kicks and movement to defend against the kicks. I will check (block with the shin) as a last resort. The ability to absorb low kicks involves sitting down (like a squat) to cut the kick off before it reaches it's maximum point of power. I use different kinds of kicks from Tae Kwon Do, Karate, and Muay Thai. You will see hook kicks, round kicks, etc. The fight will end with an array of punches until the opponents corner throw the towel in. But if you watch you will see that it was a left round kick to the liver that hurt him. The delayed reaction of the kicks was felt as the punches were being thrown.