The study was initiated by the National Institutes of Health's National Center for Complementary and Alternative Medicine and led by Group Health Research Institute in Seattle, Washington.
Low back pain sufferers were assigned to stretching classes or yoga classes or home book-based self-care. Both the stretching classes and the yoga classes were equally effective at eliminating the back pain, suggesting that the stretching aspect of yoga provides the most benefit, not the meditative portion (Jennifer Dooren, "Yoga May Help Low Back Pain. Mental Effects? Not So Much," The Wall Street Journal, Oct. 25, 2011).
Meditation is something the Bible encourages us to do, but not the transcendental meditation often associated with yoga in which, through the help of breathing exercises, the mind is emptied—which can open the mind to wrong spiritual influence. Christian meditation is restful but involves actively thinking about the ways, teachings, laws and words of the Bible as inspired by God.
From a Christian perspective, there are problems with even the physical practices of yoga. Hindu tradition asserts that the first teacher of yoga was the destroyer god Shiva—Lord of Yoga. The postures and hand positioning have pagan symbolic meaning, and some are prayer positions of pagan worship. The body positioning is supposedly to channel spiritual energies. For instance, the bodily exercises of the popular Hatha-yoga are intended to suppress the flow of energies on either side of the spine to force the kundalini (serpent power) to rise from the base of the spine through the spinal energy channel to ultimately be united with Shiva at the crown of the head. There may be nothing to this, but demons do operate within pagan religion (1 Corinthians 10:20). In any case, the whole system is part of pagan ritual.
To avoid all this, find a stretching class or routine with no connection to yoga.