Hi Alan,
Well, I would say that such is a traditional view of Chinese Medicine, with a heavy dose of Taoism, rather than strictly Buddhist or Zen Buddhist. Some old Asian Zen folks, being old Asians
of course, professed such things too. In centuries past, that is how folks in Asia tried to describe what is going on in the body before all our modern ways of doing so. Is it literally true or not? Do such energies truly exist in and around us? Well, maybe not as something that can be seen with a microscope or on a meter ... but if it helps you express in words something true, then it is useful, a poetic description. Also, much of what he is describing ... about nourishing, caring for and resting the body-mind ... is true no matter how it is called or described.
I do agree that Shikantaza is finding a balance
amid/as/through-and-through the swirling imbalances of this life-world ... a balance of body-mind. It is balance of the body in sitting, balance of the mind ... body and mind, not two. It is a Balance so Balanced, it covers both daily balances and imbalances.
Gassho, J