Anchor your legs in a decline bench and hold your fingers at the sides of your head. Crunch the trunk to push the lower back into the bench, and then hinge at the hips to sit up while rotating one shoulder to the opposite knee. Return to the bottom while maintaining tension in the abs and repeat, rotating to the other knee.
 
Purpose
The decline sit-up provides trunk and hip flexion training with resistance farther along in the hip flexion movement relative to a sit-up on the floor, and adds rotation to the motion to develop more aspects of trunk stabilization.
 
Programming
Perform sets of 10-30+ reps; if adding weight, perform sets of 8-15 reps.
 
Variations
Rotating decline sit-ups can be done with additional weight (such as a dumbbell or plate held behind the head/neck), and of course with the sit-up board at different angles.