Lie on your back with the legs straight and arms extended overhead. Simultaneously perform a sit-up and lift your straight legs, reaching the hands up to touch the toes as you create a V shape with the body. Your balance should be such that you can pause when the hands and feet meet and hold this position. Return to an extended body position maintaining ab tension and without allowing the heels to touch the floor in between reps.
 
Purpose
The V-up trains both strength and stamina of the ab and hip flexors, and provides a more challenging variation of the sit-up and jack knife.  

Programming
The V-up should be performed for sets of 10-30+ and will generally be more of a stamina exercise with higher reps.
 
Variations
The V-up can be performed by bending the knees and with the hands on the head, bringing the knees and elbows together, making the exercise a jack knife.