There are quite a few variations on hip flexion and extension flows from down dog. Here’s one called Monkey Tail. Start in Downward Facing Dog. As you inhale, lift one of the legs up toward the ceiling, bending into the knee as you lift. As you do this, pull the chest bone towards the front of your mat and look forward. Pay attention to the low back as having the knee bent makes it easy to arch the back too far. If you feel any discomfort, back off. As you lift the leg, head, and chest, you build strength and flexibility in the muscles along the whole spine.
As you exhale, bring the knee in toward the nose, and nose in toward the knee. As you do this, you continue to work the low back muscle, and as you complete the crunch, you use your abdominal muscles as well.
Repeat for anywhere from 3-12 breaths, depending on how you’re fitting it into your practice. Make sure you balance it out on the other side!