Single-Arm Chest Press with Rotation

Start: Grab a dumbbell in your right hand and lie back on a stability ball so that your body forms a straight line from knees to shoulders. Hold the dumbbell at chest height and rest your left hand on your hip.

Movement: Straighten your right arm and press the dumbbell toward the ceiling and across your chest as you brace your abs and crunch up, lifting your shoulders off the ball. Return to start. That's one rep. Do 10 to 12, then repeat with your left arm.

Tips:
Keep your glutes engaged throughtout the entire set.