I'm looking for an effective stretch for the external obliques. Can you help with any suggestions?
The external obliques' action is to flex and rotate, so when you crunch and twist to the right, your external obliques on the left side are contracting. You could stretch those muscles by extending the spine and rotating to the left. A good exercise is from the Reebok RNT program called quadruped rotation and extension. You get on your hands and knees and put your left hand behind your head as low as you can get it. Then, without moving anything else, think of rotating your left elbow up to the ceiling and think of extending, or arching, at your thoracic spine. This is working against gravity. Another option working with gravity is to get on a physio-ball and arch backwards, bringing one arm up over your head, thinking of "rotating down into the ball" as you do it. One more thought is, many people are tight in the quadratus lumborum and may need that stretched in addition or more than their obliques.