In my experience, there is a lot of difference between the elbows of Thai boxing and those of kung fu. Thai styles used the elbow far more frequently although both Thai and Chinese styles have a great variety of elbow techniques.
Thai boxing is all about inviting, and elbows are allowed in the ring. As a result upward, Crossing, diagonal, downward, jumping, spinning and stabbing elbows are practiced as often as one would practice punches and kicks.
In my experience with a log fish, we use the elbow - 4 rather we learned at the elbow - but it was it used all too frequently in application or in sparring.
I have only trained in ngo chor for a short period of time, however from what I've seen the elbow is used quite a bit, though not as much as muay thai. The usage is different also. Being a southern style, there is a lot of close-range fighting so it uses the elbow both offensively and defensively, though I haven't seen the wide variety I learned in longfist. In addition, if a punch is blocked in front of the elbow toward the wrist, they will continue the attack by bending the arm and striking with the elbow if that makes sense. This is used if a bridge has been established.
The thai elbow is relaxed in delivery and to keep the elbow tight, pointed and close, the wrist is bent on cross and diagonal elbows.
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