Errors in transmission......
Greetings,
The brief stint that I had in Tae Kwon Do, the training of the upper and middle blocks involved both hands. In retrospect, I learned that the blocks were preceded by soft parry/deflection with the other hand. Though it was never taught to me that way, the technique was there for me to recognize years later. That being said, the aggressive aspect of blocking has been de-emphasized in Karate and Tae Kwon Do. When it came to the two blocks that I mentioned, they were quickly converted into controlling grabs to set up the finishing technique or techniques. High, middle and low blocks did not constitute the "all" of the types of blocks found in Karate/Tae Kwon do. You do not see this too much now days.
mickey