This is a great video demonstration of Bikram Choudhury doing Triangle (Trikonasana). Keeping two heels in one line, when he sits down he keeps his spine in the center. Notice how he brings his hips forward and his right knee back before bringing his fingers to his toes in order to get the proper alignment and triangle formation. When his fingers don't quite reach his toes, he stretches his right shoulder down without bringing his hips up. Keeping his left knee locked and squeezing his left glute muscle he twists to the left as in spine twisting posture.
