The 21-Day Yoga Challenge: Pose a Day brings you today’s pose:
Supta Parsva Pavanamuktasana – Supine Double Knee Twist
There are a variety of twisting poses to choose from and this one can be modified. If your back needs more support keep the feet on the floor.
Cues: From a supine position, engage your core to draw your knees above your hips. Actively reach your arms out at chest level with the palms facing upward. Maintain engagement of your core as you inhale and then exhale to guide your knees to the right. Inhale and with an exhale draw the knees back to center. Inhale and with your exhale, guide the knees to the left. 
Complete 12 rounds, following the breath pattern to move knees on the exhale.
Benefits: Twists are necessary for good spinal health because rotation nourishes the vertebrae. The action of twisting contracts and releases many organs in the abdominal region which aids in flushing the organs and directing the elimination of toxins. Regular practice of twisting poses will relieve back pain, increase flexibility in the hips and help tone the belly.
Modifications: Remember you can always practice this twist with both feet on the floor. In that variation, it is nice to take the feet as wide as your mat and then let the knees drop to each side. It is fine to stay in the twist for several breaths before the exhale takes you back to center.