The Oblique or External Abdominal Oblique Muscle is used for torso rotation. There are three main muscles that help with torso rotation: Internal/External Obliques and the Transverse Abdominis. Be very careful and use precise movements while working the obliques. Using too much weight and over-rotating can compromise the back, cause injuries and future back problems. I have put together a series of eight exercises that target the oblique region. I recommend doing two or three sets of twenty repetitions at light to medium weight.
Top 8 Oblique Exercises