Many Christians claim that modern postural yoga is antithetical to Christianity, on the grounds that it forms part of the worship practices of a non-Christian religion.
This is a dubious assertion. It's true that the Paśupati seal (c. 2000 B.C.) suggests that sitting positions may have had some kind of religious significance. Indeed, for Patañjali (c. A.D. 200), sitting positions are the only kind of āsana he knows -- as the word's etymology and usage suggest (sthirasukham āsanam, Yoga Sūtra 2.46). It's not until late medieval times that a variety of poses and practices is documented (Haṭhayogapradīpikā). The modern "yoga class" turns out to be an invention of the nineteenth century, an Indianized response to European and American calisthenics classes. [1] Some poses are not attested before the 1930s.
While the posture names may draw on non-Christian mythology, there is nothing in the stretching exercises themselves that links them inextricably to worship.
Of course, if the body exercises become a gateway into non-Christian beliefs or practices, then that is another matter.
[1] Mark Singleton, Yoga Body: The Origins of Modern Posture Practice (Oxford University Press, 2010).