Lie chest down on elevated bench. Grasp dumbbells below.
Keeping upper arm perpendicular to torso and dumbbells just below elbows, pull dumbbells up until elbows are just above shoulders. Return and repeat.
If upper arm travels closer than perpendicular to trunk, latissimus dorsi becomes involved. Elbows should be raised directly lateral to shoulders. Bench should be just high enough to prevent dumbbells from hitting floor and close to horizontal. Also see exercise performed on Lying Rear Delt Apparatus. Lying at 45° is not sufficient angle to target rear deltoids. Much lighter resistance is required as Dumbbell Lying Row.