Often in conversation people mention that Yoga is a good idea. When a Catholic begins saying this then it is worrying. Why? Isn't Yoga just a physical exercise? Can't we just use the ritual movements and positions but not subscribe to the belief system underlying them? I am sure you are familiar with these questions.
As a Catholic it is not possible to believe that the postures and physical expressions of belief are useful when separated from the beliefs they are linked to. We know from our worship and prayer (especially the ultimate prayer of the Mass) that each movement and posture is meant to convey a deep spiritual meaning. The Sacraments give us a way of physically experiencing a deep reality. The physical part of the Sacraments is integral to their meaning. As limited creatures we can only experience the Spiritual realm through our senses. The Sacramental actions help us to experience God, they physically put us in touch with our Creator. As a believing Catholic you would consider someone who is not a Catholic and just comes to Mass to "stand, sit, stand, sit, stand, kneel, walk, kneel, stand" as crazy. To remove the spiritual reality which is integral to the actions causes all reasoning to disintegrate.
The same must hold true for Yoga. Yoga is based on a Hindu belief system. The point of yoga is to enter into unity with the great Brahma, or to experience reality as understood by Hinduism. There is no doubt that yoga is a Hindu form of meditation.
Can a Catholic practise yoga if they disconnect from the spiritual side of it? This is not the right questions to ask. Rather, we should ask: Is it possible to remove the spiritual side from the actions and still have an integrated spiritual life? The answer is NO. Every physical action has a spiritual side, to not recognise this is to cause our identity as spiritual/physical being to disintegrate and we will be set back in our pursuit of Heaven.