Something I've noticed in MMA is that roundhouse kicks - whether they're karate or muay thai - seem alot more effective than straight kicks like side kicks and front kicks etc.
I think this has more to do with that the kicks are designed for and the individual fighter's style.
That is to say the round kick is extremely damaging, there are very few kicks I would consider more able to damage the body (spinning back kick, and spinning heel hook being the only ones). While the front thrust/snap as well as the side kick are designed to control range and set up other strikes whether they be rotational kicks or punches.
There really aren't many fighters who use a stick and move strategy with their feet, and thus don't put much effort into, and use less often, the linear kicks. I try to use kicks for this purpose and have found that while they're not nearly as powerful as a round kick, they are much more surgical in my opinion.
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