MAIN MOVE: Starfish

Get into push-up position on knees, hands directly beneath shoulders with light dumbbell in left hand. Engaging abs to stabilize torso, raise left arm straight out to side, parallel to floor. Hold for a second, then slowly lower to start and repeat. Do all reps, then switch arms.

MAKE IT HARDER: Bring your knees off mat so you're balancing on toes and hands as you do the reps.

MAKE IT EASIER: Ditch the dumbbell.