Tight external hip rotators can be a pain in the butt, literally, and give you lower back pain. Loosen them up to rebalance your body.
One last caution: Some people externally rotate their legs because of an anomaly in the shape of their femurs or in the orientation of the hip joint itself. If you feel discomfort in your knees, ankles, or feet as you work to reduce your external rotation, you may have one of these structural anomalies and should be checked by a knowledgeable health care provider or an experienced yoga teacher well trained in anatomy and kinesiology. But if your only difficulty is the hard work of internal rotation, I urge you to persevere. Your internal rotators may grumble and complain, but with time and practice, they'll grow stronger, and your whole physical structure will benefit from a better-aligned foundation in your legs.
A licensed physical therapist and certified Iyengar Yoga teacher, Julie Gudmestad runs a private physical therapy practice and yoga studio in Portland, Oregon. She regrets that she cannot respond to correspondence or calls requesting personal health advice.