Physical Therapist, Shirley Sahrmann states in her book, Diagnosis and Treatment of Movement Impairment Syndromes, "Rotation of the lumbar spine is more dangerous than beneficial and rotation of the pelvis and lower extremities to one side while the trunk remains stable or is rotated to the other side is particularly dangerous." Sahrmann notes that "The overall range of lumbar rotation is approximately 13 degrees. The rotation between each segment from T10 to L5 is 2 degrees. The greatest rotational range is between L5 and S1, which is 5 degrees. The thoracic spine, not the lumbar spine should be the site of greatest amount of rotation of the trunk.”
You must understand that the primary role of the abdominals is to provide isometric stabilization and limit the rotation of the lumbar spine. If you are doing any of the following stretches/exercises, my advice is to stop before you have to chase one of your vertebrae down the street.
DN