http://irkrs.blogspot.co.uk/2013/04/siamese-boxing-original-source-of.html
Who would have thought that the origin of karate strike was Muay Boran....or the ancestral art to Muay Thai!
Indo-China

Satisfied that I had successfully located the original sources from which came Tegumi, Torite and Kata, my efforts to trace the origins of Tigwa proved a bit more challenging. Exhausting my search of Chinese, Korean and Japanese sources, and considering the possibility the plebeian art may have evolved indigenously, I remembered Kerrs comments and was pleasantly surprised to learn that for more than a thousand years both China and India had influenced the development of local fighting arts in SE Asia. Henceforth I widened the scope of my study. In spite of the many remarkable fighting traditions I found in Indonesia, Malaysia and the Philippines, etc., none seemed to resemble the simplicity of Tigwa. The only other culture in which I could locate a tradition of similar qualities, within reasonable geographical proximity and contemporary historical timeframes, was the old Kingdom of Siam and its ancient art of boxing, Muay Boran.
If it has Feathers, Quacks & Flies...its a Duck! 

I learned that Muay Boran [lit. ancient boxing] -using the very same tools as Tigwa (i.e clenched fists, head, elbows, knees, shins and feet)- was hugely popular especially during Thailands old Kingdom of Siam Period. Adding to the plausibility of this theory, I also discovered that Ryukyu ships had vigorously plied the waters between the two cultures, conducting a bustling commerce, for more than two hundred years during the old Ryukyu Kingdom Period! While all this seemed quite promising at the time, I still had a problem seeing the link between Muay Boran and Ti-gwa.
At first glance the differences appeared obvious; after all, everyone knows that the Kingdom of Siam became The Kingdom of Thailand and Muay Boran became Muay Thai [Kick boxing]. Muay Thai, in its modern form, looks nothing like modern sport Karate, and vice-versa! Try as I might, I still was having difficulty reconciling the precise simplicity ofkumite and dynamic elegance of kata performance with the modern sport of Muay Thai! Perhaps I was focusing too much upon Thai fighters dressed in silk boxing trunks, wearing gloves, a liberal rubbing of pre-fight liniment and wailing on each other in a ring, which allowed knees and elbows!
Who would have thought that the origin of karate strike was Muay Boran....or the ancestral art to Muay Thai!