The transition between the first and second movement is a keypoint of Pinan Shodan. Keypoints always carry specific messages that cannot be found easily in other movements. The point is to be able to move the upper and lower section of the body independetely from each other. As you close the upper body (squeeze), the lower body may not be affected. Do not destabilise your posture. Points to note are an intact Seichusen and the position of the right knee, which should be virtually unaffected by the movement. A common error is to collapse the right knee, as many also do in Naihanchi.