Can you offer an explanation as to why the shoulders should lift up and rock forward at the end of a shomen cut? And why the tip of the bokken wobbles around like it is the end of a spring?
I had the chance to look at the video with sound last night and the thought occurred to me that the tension might not actually be in Saito Sensei's shoulder muscles, but rather in his whole body, as he is expelling a fairly forceful kiai as he completes those cuts. it still really looks like his sword and arms are separating from his center at the end though.
Probably a side effect of to much tanren uchi (on a tire).