How to do Oblique crunches
Begin lying on your side with the legs slightly bent and stacked one on top of the other. Place your bottom hand on your tummy (so you can feel your side abs) and your top hand behind your head with the head resting on the ground.
Crunch your top elbow toward your top hip bone as you raise the head and shoulders off the ground slightly.
Then, lower back down to the ground and relax your head.
Repeat for the desired repetitions, on both sides.