When and how did mainstream kickboxing switch from the karate kind of kick (snap, instep) to the muay thai type? (no snap, shin).

As far as I know, kickboxing was born from "full contact karate", but now it uses muay thai kicks... not so in the 70's. What happened?

If I'm not mistaken, using the shin to strike with isn't allowed in most American kickboxing leagues. In MMA however, the trend has been in favor of the shin for most round kicks. This is due in part that the shin is harder to seriously damage than the instep. Muay Thai people generally use the shin as well, and given the popularity of Muay Thai nowadays, its no surprise that method has caught on in other sports.

Like Drew said, the shin strike does a lot more damage to the opponent. I think you're able to get more torque with the hips and follow through.

Using the instep, you're more likely to overextend the ankle.

Drew and JGarner890 makes some great points, in which I wholeheartedly concur with. Both, imho, types of kicks are very effective as well as they both have their pros and cons, however, I believe that if given a choice, the shin type can provide much more damage in totality because the shin type can be akin to swinging a tree-trunk.

Is it method over idea or vice-versa when one thinks about either of the two?

In my second pro fight, I threw only two snapping leg kicks with my instep. Though they sting, I doubt they hurt deep. The shin however, deep pain.

I myself like to kick with the shin on the side of my opponents knee. Possibility of seriously hurting them.

Like Drew said, the shin strike does a lot more damage to the opponent. I think you're able to get more torque with the hips and follow through.

Using the instep, you're more likely to overextend the ankle.

This is exactly why Muay Thia and MMA use the shin. It breaks your opponents body down quicker with little risk of injuring ones self as with the instep type kick. Look at the Cung Le vs Frank Shamrock fight for instance. Cung kicked Frank in the arms to slow down his hands and eventually broke his wrist.

Like Drew said, the shin strike does a lot more damage to the opponent. I think you're able to get more torque with the hips and follow through.

Using the instep, you're more likely to overextend the ankle.

This is exactly why Muay Thia and MMA use the shin. It breaks your opponents body down quicker with little risk of injuring ones self as with the instep type kick. Look at the Cung Le vs Frank Shamrock fight for instance. Cung kicked Frank in the arms to slow down his hands and eventually broke his wrist.

That's a great point because I'd rather break him/her down than the opposite; breaking me down...not a good thing!!

Yeah, Cung Le is my idol. Before I retired from fighting, I tried to base my fight style like him. Worked out for the most part, but I liked the ground game too much.

Yeah, Cung Le is my idol. Before I retired from fighting, I tried to base my fight style like him. Worked out for the most part, but I liked the ground game too much.

I concur...Cung Le is an amazing fighter across the board!!

I think this fight illustrates what a technical fighter he is, also that he can take a punch too;