To come into Supta Padangusthasana, lie flat on your back with legs together and the spine straight. Inhale as you lift your right leg and catch your big toe with your right hand. Exhale as you pull the leg toward you and contract your abdominals, lifting the scapula from the mat, to touch your nose or chin to shin. Create resistance between the arm and leg to activate the posture. Press your left heel down into the floor. This is position A. Stay for 5-10 breaths.
Inhale as you lay your body down and straighten the arm, keeping your grip on the toe. Exhale as you swing the leg to the right, opening the hip, and turn your gaze to the left. Use your left hand to press the left hip/thigh firmly to the mat. Keep both sides of the body long and, again, create resistance by pushing the foot into the grip of the hand. This is position B. Hold for 5-10 breaths and feel the foot drift closer to the floor with every exhalation as the adductors of the groin and inner thigh release.
If flexibility does not permit you to grasp the big toe with your leg straight, bend your knee as needed or use a strap around the foot. There is a tendency, particularly in position B, for the opposite hip to lift away from the floor. Do your best to keep both hips on the mat.