This is a variation of crunch exercise. This exercise is to strengthen your obliques. Secondary muscles that are strengthened are rectus abdominus / abs.
Position:
Lie supine on floor or bench with knees and hips bent. Hold plate behind neck or on chest with both hands.
How to do:
Flex and twist waist to raise upper torso off surface to one side. Return until back of shoulders return to surface. Repeat to opposite side alternating twists.
You should to push your neck. You can do this weight without any weight if you find it difficult doing with weights. Your neck muscles must not be strained when your do your exercise. This exercise is mainly targeted towards your obliques. Here are the video demonstrations on how to do this exercise.
Video Demo 1

crunches Twist – Watch more Funny Videos
Video Demo 2

Tagged: abs workout, obliques