Yoga: Fitness, Spiritual or Both?

I've joined a step aerobics class at one of our local Leisure Centers. The last time I was enrolled in a step class was ten years ago! I have noticed a few subtle differences in the last decade. First, in the beginner class category, there is a 5:2 ratio of yoga classes to step classes. Second, the step class includes several strengthening exercises that are yoga inspired. Third, the relaxation music utilized during the final stretch session is reminiscent of sounds that gently drift out of a Hindu or Buddhist temple. Lastly, phrases such as "inhale the positive, exhale the negative" are used.
I do not have a problem with my step class. It invigorates me, especially since winter temperatures and icy streets have dampened my joy of walking outdoors. However, I am fascinated how yoga has gained momentum in Western society. Yoga inspired clothing chains, such as lululemon athletica, are a testament to this fact. Also, I am wondering, is yoga a fitness activity, a spiritual exercise, or both?
I've done a bit of research on the topic. My short answer is, "It depends."
Yoga originated in India as a method to control the body in sustained positions of meditation. The goal of the meditation is to become one with Brahma, the Universal Reality. In other words, the desire of the yogi or yogini is to reach enlightenment where man/women and god are one and the same being. The word yoga itself means "union".
The Christian community seems to have many opinions on participating in yoga. Some people believe that a person can engage in the various yoga positions and benefit physically without being in a state of meditation. In this case, yoga is merely a fitness activity with no spiritual significance. Others believe that it is difficult to divorce the fitness from the philosophy. For instance, the cobra pose (Bhujangasana) is associated with praying to the awakening of creativity. If a person assumes this position, then he or she could be entering a stance of worship. The solution? Avoid yoga or participate in a Christian alternative of yoga with completely different positions (ex: PraiseMoves). One example of a "Christian" pose is The Eagle stretch, "...where the arms are pulled back to resemble a bird in flight. While students hold this stretch, [the instructor] reads Isaiah 40:31," (Source: Today's Christian Woman). Yet, there are many individuals who are advocates of "Christian Yoga" where one can carry out the traditional yoga postures while focusing one's mind to God's voice. This view is based on Psalm 46:10, "Be still and know that I am God," where the "I" refers not to humankind, but God.
Clearly, this is not a black and white issue. Personally, I would not feel comfortable in a yoga class where the instructor was verbose in eastern religious rhetoric, thereby encouraging me to engage in Hindu spirituality. However, I am not averse to the occasional use of yoga positions for the purpose of toning my muscles. For instance, in my step class, we assumed a modified boat pose (Navasana) to strengthen the abdominal muscles. And I felt okay about it.
All of this debate about yoga helps me understand why several women of the Christian faith are more comfortable with pilates instead of yoga. But that is another topic...