There is so much free information on the internet now that you can gain a very high level understanding of topics usually reserved for academics in a short time. When I started training around 5 years ago I had exactly the same questions as everyone else. So I researched them. I found out that shin conditioning is essentially an increase in bone density, and thus an increase in the strength of the bones as well as a deadening of the nerves.
If you kill your nerves (by rolling bats or balls down them) you will kill the nerves without strengthening your bone which will lead to you kicking harder than your shins can handle. They will break. If they don’t break they will be continually weakened and you will develop a host of problems in later life.
Micro fractures in the shin cause a lot of pain as the bone is forced to regrow to heal. This is a last ditch attempt by the body to stop the bone breaking. Pain is a signal to let you know your body is in danger, you should probably listen to it. That doesn’t mean give up whenever you feel a twinge, but if you get a sharp pain that makes your gut wrench during training, stop. What’s the point in strengthening your body if you have no legs?
When you kick a bag, you are strengthening muscles, tendons, cartilage and bone. You add stress to these in order to stimulate a variety of responses. Muscles act and heal in a different way to bones because they serve different purposes. When you put stress on your bone (such as when lifting weights, kicking a heavy bag, or running) you are encouraging osteoblast cells which remodels the bone i.e. makes it thicker. When you kick the bag for reps, you are strengthening your muscles, tendons and bones, not to mention your cardio as well as your increase in technical skill.
Over a period of around seven years, every cell in your body is regrown and replaced, including the cells which make up your bones and nerves. I last fought two years ago and shin on shin contact registered but didn’t hurt. Now if I knock on my shins with my knuckles it hurts like hell. If you stop training for a while, don’t expect to be able to kick bare shin full force without pain.
Thais kicking banana trees has been popularised because people don’t know what a banana tree actually is (it is like kicking rubber) and they don’t realise that the Thais kicking banana trees do so out of necessity and poverty. They punch and kick bags of rice too and hang coconuts from rope to train hand speed and head movement. You think guys like Sudsakorn, Yodsenklai, Saenchai, Nong-O etc kick banana trees or punch bags of rice? No, because they have already fought their way out of poverty and now train with great fighters and kick the heavy bag. Just because poor Thai kids with one eye on a Rajadamnern belt when they grow up have to eat bullfrogs for lunch doesn’t mean you should also eat bullfrogs to become a better Thai boxer.
I’m sick of the really awful and dangerous information given by “experts” on the internet, caused in part by stupid kids being too lazy to do their own reading. Like I said, the internet is full of information, but it is also full of idiots. Why would you trust the use of your legs to someone you have never met and whose statements cannot be verified? Go and check everything said here with a doctor, or a medical professional. Hell, e-mail or telephone a medical student. Go buy a medical or biology textbook and study. Buy an anatomy book and verify what I’ve said, I’m sharing what I have learned on my own. If it is wrong then come back and tell me. You’ll probably be saving my legs.