Subin,
do you have a link to the article on muscle control?
There is a difference between MVC (maximum voluntary contraction) for an isolated muscle and Irradiation for lifting "max" weights etc...
to stick with the biceps example - How many Chin ups would you get if you "isolated" your bicep vs. how many chin ups would you get if you had your lats, abs, arms etc.... all working in the chin up?
It is simply "right strategy for the right moment"
But we also have to consider that muscles never really work in "isolation" but rather function in patterns working together as agonist and antagonist to "balance" force, joint position etc.... Look up "Lumbard's Paradox" (how the quads and hams work together in standing up out of a chair)
Which muscle should be relax for the DL? None of them IMO
Pavel's description of the dominata is great - "enough tension to enhance the lift but not so much tension that it becomes the goal of the lift"