Any of these exercises can be done with your torso twisted at an angle.

Crunches: Lay down on a mat on the floor, bending your knees slightly so your feet are flat on the floor. Curling your hands behind your head, slowly lift your shoulders off the mat, squeezing your abdominal muscles with each raise. Be sure not pull your neck upwards; rather make it a natural, smooth-flowing motion. Lift only your shoulder blades off the mat and hold that position for a span of two seconds before slowly releasing the shoulders back to the mat. Be sure not to let your shoulders completely rest on the mat before beginning your next repetition. Do three sets of 30 reps, taking only a few seconds of rest between sets.

Knee Ups: Sit on the edge of a bench, grasping on the sides of the bench with your hands to maintain steady balance. With your legs extended outward, slowly pull your knees into your chest, squeezing the abdominal muscles during the contraction. Hold this position for two seconds and then slowly extend your legs before repeating the motion. Try to keep the rocking and bouncing at a minimum. Do three sets of 25 reps for this exercise.

Knee Raises: Find a firm grasp on an overhead chin-up bar with your arms spread slightly wider than your shoulders. Make sure that your feet are not touching the floor. Trying not to swing or rock, slowly bring your knees toward your abdomen so that your knees are locked at a 90 degree angle. Squeeze your abs and hold for a moment before slowly releasing your legs back to a straight position. Wrist straps are often used to assure a firm grip on the bar. Attempt three sets of 10-15 reps per set.