Double Crunch (Bench)
This is a stepped-up version of your basic crunch. Using a bench to create instability makes our abdominals work overtime to stabilize our body. Our obliques will also pick up some slack here to keep us in control throughout this movement. There is no rest during this movement, so our abs are in constant tension throughout the entire exercise. Sit perpendicular on your bench and grip one side. Lean back and extend your legs (your body and the bench should look like an "X," not a straight line). In one movement, bring your knees as close as possible to your chest, while curling your spine forward. Fully extend again and repeat.