START: Lie face-up on the ground with your hands extended at your sides, feet up and thighs perpendicular to the ground - both your hips and knees should form a 90 degree angle. MOVE: Slowly bring your knees toward your chest, lifting your hips and glutes off the ground, and try to maintain the bend in your knees throughout the movement. Return to the start under control.*Note: you can make this harder by doing it on a decline bench with your head on the high end.