Muscles involved: Internal and External Obliques, Quadratus Lumborum and Transversus Abdominis
Action: Lie on one side with your top hip stacked above your bottom hip. Raise yourself up until your body is in a straight line through your feet, hips and head. Lower your body back down under control until your hips barely touch the ground. Repeat this sequence for the desired number of repetitions. Then switch to the other side and repeat.
Comments: This exercise should be done without using any rotation to get yourself up. Once you develop some strength, progress to holding your side up while raising your upper leg into hip abduction for a series of repetitions.