My introduction to Muay Thai came at the hands of “Master” Chai Surisute in the Smoky Mountain Martial Arts Camp in July of 1987. Two hours a day in the hot sun, Chai tortured us with Thai pad drills and Plum Grappling. His power is legendary and he can nearly knock out the holder of the pads with his roundkick.
The cardiovascular demands and localized muscular endurance inroads of Thai impact resistance work exceed anything you can imagine. This is not your soccer mom’s Tai-Bo class. This method was taught by Chai as a life saving art. He firmly believes the man standing after the fight is the true master.
Punching pads or swinging weights with your arms brings large amounts of muscles into play. Driving your whole being into a kick designed to shatter a femur (thigh bone), calls upon the lungs and muscles in an severe way that tests you to your soul.
Here is a simple example of a workout by a Thai Boxer.

http://www.youtube.com/watch?v=3NXPuZsdoUk