MAIN MOVE: Sit-up pullover

Lie face up on floor, knees bent, feet flat, and arms extended overhead with a light dumbbell in each hand. Contract abs and slowly curl up, lifting head, shoulders, and back off floor. Simultaneously bring arms forward in an arc toward knees. Hold for a second, then slowly reverse to start.

MAKE IT HARDER: Add a chest press. With upper body lifted and arms in front of you, bend elbows and lower dumbbells toward chest, then straighten arms before returning to start.

MAKE IT EASIER: Keep head on floor as you raise dumbbells in an arc and bring them down to floor so arms rest at sides. Reverse to start.