This challenging sit-up exercise is excellent for working your core region. Beginners can start off with the standard V-sit (with one leg extended) and advanced users can use the progression (with both legs extended).
Step By Step Instructions
Lie on your back with your knees bent and your heels on the ground. Straighten one leg out on the mat, and raise your arms overhead.
Lift your upper body and your leg together in a v-motion. Repeat for 5 repetitions, and then repeat with the opposite leg extended.