Start on all fours on a yoga mat. Ensure that your knees are directly below your hips and your hands are directly below your shoulders.
While maintaining a neutral spine and stabilizing through your abdominals, place your right hand on the back of your head, drawing your shoulder blades down and back.
Inhale, and slowly rotate your torso to the right, opening the right side of your chest and pointing your elbow toward the ceiling, or as far as you can go while maintaining a neutral spine and keeping your lower body as still as possible. Hold this position for one to two seconds, breathing deeply.
Exhale, and rotate your torso to reach your right elbow toward your left hand (for a deeper stretch, you can also choose to lengthen your arm all the way through, as shown). Hold this position for one to two seconds, breathing deeply. That's one rep.