Stand with your feet together, and hold a light dumbbell in each hand. Start with both arms up above your head, your arms slightly bent at the elbows and your palms facing each other.
Keep your core engaged, and lower your right arm halfway down to the side to shoulder height. Your arm should remain in the same slightly bent elbow position.
Raise your arm back up, and repeat on the left side. Keep alternating arms, and complete 20 reps total.