I enjoy the modified Up Dog Down Dog because it is very good for the spine. Specifically, the lower back and sacral area. This exercise becomes a rhythmic traction type of movement for the lower part of the spine which helps increase flexibility and reduces pain. When people have a great deal of pain and have a hard time finding a comfortable position the down dog portion of the stretch can provide that comfort. In fact, if this is a position that feels good to you I would recommend staying in the down dog for 5 to 10 minutes while taking large slow breaths. I think of the up dog portion of the stretch when people have discomfort in the upper mid back. Its a great way to undo hours of sitting at the computer or in the car.