Pink is one of the fittest celebrities out there and is known for her incredible abs.
Along with kick boxing, she devotes a lot of her time to pilates and moves like this to keep that incredible ab definition.
I don't think this move alone will get you Pink-ripped, but its a good start!
"Long Leg Rotation
Lie faceup with legs extended over your hips, hands behind head, and elbows pointing out to the sides. Crunch up, lifting your head and shoulders. Lower your left leg toward the floor as you rotate to the right, bringing your left elbow toward your right knee. Return to starting position; repeat on opposite side. Do 20 reps, alternating sides each rep."