Start in your plank position with your shoulders in line with your wrist, your shoulders down and back, and your spine long. Lift up out of your shoulders, engage your core, press out through your heels, lengthen, and breathe.
Engage your core even deeper as you exhale and float your right leg up without arching your lower back.
Take your right leg down to plank, and repeat on the left side. Point through your toes and lengthen your leg as much as you can. If you feel your lower back arching, don't lift your leg as high; keep the movement really small and go for the length over height.
Repeat for 50 seconds, then hold Child's Pose for 10 seconds.