Most weight exercises can be divided into two basic types: isolation exercises and compound exercises. As the name implies, isolation exercises focus on specific portions of a muscle, such as training the upper back and the lower back. Or it can be even more specific, such as targeting one of the three portions of the deltoid or shoulder muscle. The deltoid has three main sections, the anterior or the frontal portion of the deltoid muscle; the lateral or side head; and the posterior or rear deltoid. Specific isolation exercises are designed to concentrate on each of these separate portions of the deltoids. For example, the front raises with dumbells or a cable in which the arms are raised in front of the torso to isolate the anterior portion of the delts. To hit the side delts, any type of lateral raise, in which the resistance is raised from the side is considered the best way to isolate this portion of the deltoids. For rear or posterior delts, bent-over laterals with either dumbells or cables are effective, although in recent years seated rear delt machines have become more popular.
Isolated deltoid training is considered essential to developing outstanding deltoids. A compound exercise for the delts would involve working not only the isolated delt portions but also accessory muscles that work with the delts in raising the upper arm. The best example of this is any type of overhead pressing exercise. Years ago, I was provided with a workout routine by a world-famous bodybuilder who had won numerous international titles, including several Mr.Universe titles. The workout he gave me contained only pressing exercises for the shoulders with no isolation movements such as lateral raises and so on. Since I had always done some type of isolation exercise when I trained my shoulders, this lack of isolation exercises concerned me. The famous bodybuilder told me that presses work "all parts of the shoulders," so that all three deltoid portions would be trained simultaneously. I had usually included at least one type of overhead pressing exercise in my shoulder routines. The reason for that inclusion was the widely held belief that pressing exercises permitted lifting far heavier weight compared to isolated shoulder movements, so would be more likely to produce thicker shoulder development.
In point of fact, overhead presses of any type are not an isolation exercise and they do work other muscles besides the deltoids, such as the upper back and triceps. But the portion of the delts that they actually work are mainly the frontal delt portion, with only minor contributions from the side and rear delts. Thus, doing only pressing for shoulders would produce great development in the frontal portion of the delt, but it would be out of balance with side and rear portions. For complete deltoid development, separate . . .