Kenneth says that the Hindus know that every "asana", or yoga pose, is linked to a Hindu Deity. Well, some Hindus have also linked every vowel and consonant to a Hindu Deity as well -- or to be more precise, to a Divine aspect.
Do the Hindus have a monopoly on shavasana, just because it may be linked to an aspect of the Divine as understood by Hindus?
The problem is, that the Hindus invented Yoga out of spiritual need(tool for meditation), spiritual search and they linked it to a Hindu Deity. Yoga was at the very beginning impure and unholy. Vowels and constants didn't came into existence out of a spiritual need. It's a part of our nature. And sure, you can link a part of your nature to a deity, it's just a misuse of the nature, of the original purpose. But Yoga is not a part of our nature; there's no neutral root of Yoga. And today people try to make from a unholy, impure thing, something neutral. :/
And why should I use relaxation practice with Yoga, to calm with it "shattered nerves and relieve sensations of fatigue"? I think a spiritual person (I'm not) don't need that or somebody who tries to be spiritual (in an orthodox way). When you live daily in an atmosphere of repentance, you'll by and by overcome your physical and mental weakness. And when you try to overcome it with Yoga, you'll not learn to overcome some weakness by Grace of God.
For example when I use Yoga against impure thoughts, then Christ will loose more and more his role in your spiritual way of salvation, of theosis. When I use it against mental weakness, that I'll never learn to overcome it with the grace of God, with prayer, with humility, with repentance.
Yoga is so attractive, because the effect comes very fast. But the orthodox way of life is a battle, and some effects come just after some months or years. And so (orthodox) people try to overcome some "neutral" part of their life with Yoga.
I think in general
people who practiced Yoga before they became orthodox, they stop with it, because they know and feel the danger, but people who start with Yoga as orthodox believer they've difficulties to understand the danger of Yoga.