Lie prone on incline bench with shoulders near top of incline. Knees can rest on seat or legs can be straddled to sides. From elevated platform or partner, grasp dumbbell and position palms forward.
Raise dumbbells until arms are flexed. Lower dumbbells until arms are fully extended. Repeat.
The long head (lateral head) of Biceps Brachii is activated significantly more than short head (medial head) of Biceps Brachii since short head enters into active insufficiency as it continues to contract. Also known as Dumbbell Spider Curl.