Start: Grab a pair of dumbbells and lie on a bench. With a neutral, shoulder-width grip and straight arms, hold the dumbbells up over your forehead.
Finish: Bend at the elbows as you lower the weights down to the sides of your forehead. Keep your upper arms in the same position, and pause when your elbows are bent just past 90 degrees. Return to the starting position.
Keep one dumbbell in the top position while the other arm performs the movement, then switch to complete the repetition. Or raise one dumbbell at the same time that you're lowering the other.