The setup: Stand with your feet slightly apart and your knees slightly bent. With your arms fully extended (but not hyperextended) above your head, hold one dumbbell, using an interlocking grip.
The move: Contract your abdominal muscles. Gradually lower the dumbbell back behind your head and neck while keeping your elbows in place above your head. Continue until your forearms are parallel to the floor. Pause for a second, then gradually raise the dumbbell to the starting position. Control your movements throughout the entire exercise, inhaling while lowering the dumbbell and exhaling while raising it back up. Continue until the entire set of 8 to 10 repetitions is complete. If you are performing multiple sets of this exercise, take a deep breath, wait 15 to 30 seconds, and begin your next set.
Tip: Maintain your posture throughout the entire exercise; avoid arching your back.