That's an interesting clip. I need to study it more along with what he's saying. However, with my cursory glance, what is gained by performing this exercise with tension, over remaining as relaxed as possible? I'm asking because, I'd be worried that an exercise, such as this, performed with "tension" might encourage unnecessary tightness in the shoulders and lower back. Unless I'm misunderstanding your use of the word, "tension"? Not to mention an implied amount of previous training that would supposedly address these issues?