Position two dumbbells to sides, palms facing in, arms straight.
With elbows to sides, raise one dumbbell until forearm is vertical and thumb faces shoulder. Lower to original position and repeat with alternative arm.
The biceps may be exercised alternating (as described), simultaneous, or in simultaneous-alternating fashion. When elbows are fully flexed, they can travel forward slightly allowing forearms to be no more than vertical. This additional movement allows for relative release of tension in muscles between repetitions.