The dumbbell pull-over to skullcrusher is a complex that combines two popular exercises into one sequence that works much of the upper body, particularly the chest, triceps, and serratus anterior muscles. Because the pull-over will determine the amount of weight you can use, this movement is usually performed for moderate to high reps, such as 8-12 reps per set or more, as part of the upper-body portion of a workout.