Barbell or Ab Wheel Rollouts. Using a barbell loaded with 25 or 45 pound plates, or an ab wheel, kneel and place your hands in a comfortable position. Slowly roll the bar forward until your body reaches a near horizontal position. From here, roll the bar back to the starting position and repeat.
Decline Bench Knee Raise (Reverse Crunch). Lie on a decline bench in the opposite position, with your head higher than your hips. Grab the padding of the bench somewhere near head level. Raise your knees, attempting to touch them to your elbows, then lower your legs and repeat. For added resistance, use ankle weights, or secure a cable pulley or resistance bands to your ankles/feet.
Side Plank. Start by laying on your side with one hand on the floor and your feet on top of one another. If you prefer, you can rest on your elbow instead of your hand. Lift your hips up until your body is exactly straight. Now hold this position for as long as possible. You should feel this exercise in your abs and obliques. Do not let your body sag in the middle; always stay perfectly straight.
Mountain Climbers. This exercise can be performed with your hands on the floor, on a bench, or upon an exercise ball. Start in a push ups position, with your arms locked and your body straight. Keeping your body still, raise your right knee towards your left elbow, and then return it back to the starting position. Repeat this motion, bringing your left knee towards your right elbow. Continue this climbing motion for the required number of reps.
Hanging V-Style Leg Raises. Hanging from a pull ups bar, raise your legs until they are parallel to the ground, keeping them somewhat straight or in a locked position. Instead of returning your legs to the starting position of the exercise, flare your legs out until they form a V-shape. Bring them back together, keeping your legs parallel to the ground. Return to the starting position and repeat.