The present day exercise of zazen in a Zen center and even a Tibetan center seems to be more of a discipline related to docile bodies, docile in the sense of submission and obedience. The emphasis is much more on the za (坐) of zazen, which is sitting, than zen (禅) which is contemplation that aims at awakening or satori.
The physical za is easy to see and to do for most people. It is a body sitting very still with legs crossed with the hands in a particular mudra. But such docility does not necessarily carry over to the zen side of zazen. I would argue, in some respects, both are quite different.
Making the body docile in the practice of zazen reaches its apex in Japan with Dogen Zenji's shikan-taza which, literally, means just tend to sitting (只管打坐). In Chinese Zen or Ch'an it refers to those who didn't have responsibilities in the large public monasteries. In other words, they just sat (只管打坐 ) and drank tea and basically did nothing. This might be called spiritual laziness since the most active Zen practice in China, at one time, was seeking encounters with enlightened masters.
Dogen's shikan-taza might well be described as a misunderstanding on his part or a clever invention of his to market his own brand of Soto Zen in Japan which would fall under the expression of "selective" (senjaku) Buddhism.
"This term, taken especially from Pure Land theology, refers first to the selection from a multiplicity of spiritual exercises (shogyô) of one practice for exclusive cultivation (senju). In Pure Land itself, of course, this practice was the recitation of Amitabha's name (nenbutsu); for Nichiren, it was "discerning the mind" (kanjin), understood now in its esoteric sense as the recitation of the title of the Lotus Sutra (daimoku). For Dogen, it was just sitting. In one obvious sense the selection can be seen as a simplification of Buddhism and a reduction of its practice to a single, uncomplicated exercise accessible to all" (Carl Bielefeldt, Dogen's Manuals of Zen Meditation, p. 165).
There is enough grist for the mill to permit specialists of Soto Zen to find a reasonable explanation as to why Dogen focused so much on the za and very little on the zen side of zazen. Nothing that I have seen from Chinese Zen can justify Dogen's shikan-taza practice. The docile body is not a proper vehicle. Mind is. Sitting for long stretches of time is not a spiritual activity so much as it is a crude attempt at calming the Five Aggregates which as we all know belong to Mara, the Buddhist devil. We are not whipping the horse (mind) but, instead, whipping the cart.