“The lateral is the most popular deltoid head, as it is the one that contributes the most to shoulder width. Steve Reeves was one of the leading proponents of developing this muscle, and it was really a sight to see him working them. He used to do Incline Seated Laterals until the area fairly burst with blood!
Although the lateral head of the deltoid is the most popular of the three, it is not the one worked the most – the anterior (front) head gets that honor. Sounds rather confusing doesn’t it? Well, the answer lies in both the fact that Dips, Presses, and Bench Presses work the anterior head very strongly, and also the fact that most bodybuilders simply use improper form in doing their lateral deltoid work.
Finally, we come to the posterior (rear) deltoid. This poor fellow hardly gets any work at all. It’s just left to fend for itself, growing through auxiliary exercises alone. If Nature was quick to do away with dis-used bodyparts, the posterior deltoid would soon atrophy into non-existence.
Yet this lowly muscle is extremely important in developing depth in the shoulder region, for without it the shoulder will appear flat from the side. It appears flat because that’s just exactly what it is – flat.
We have a saying around Vince’s Gym. “Sure, he looks good from the front but is he a surfboard?” You’ve all seen surfboards or pictures of them. They are wide and very, very flat. A “surfboard” bodybuilder is just the same — wide but flat. They have no posterior deltoids at all. If you want this thin and round-shouldered appearance – OK. But if you want the well-rounded look of a champion, then posterior deltoid work is a real must.” Larry Scott, Advanced Deltoid Routines