Complete each of these moves back to back with no rest 3-5 times. Rest little between supersets (no more than 30 seconds)
Cross-Leg Reverse Crunch (15 reps/side) – Lay on your back, rotate right hip out and place the outside of your right foot over the left knee. Do a reverse crunch lifting the left leg (with right crossed over) up and raise left foot to ceiling. Lower leg without touching the ground and repeat. Complete all reps, then switch legs, crossing left over a straight right leg.
Easy modification: Bend the leg that you are lifting off the ground.
Hard modification: Lay on a bench with your legs over the end, so that your legs never touch the ground. (see pic)
Plank Hip Twists (15 reps) – Start in plank, on elbows. Keeping legs and back straight, lower the right hip to floor. Return to plank and repeat to the left. (1 rep). Pivot at your feet – you should use your obliques and abs to lower and raise your hips.
Hard modification: Rest elbows on a bosu ball or ugi ball. This will add instability and make it harder work on your abs.