In an article discussing chest development it was stated that “…bringing your shoulders forward on pressing movements involves your shoulder and back muscles to a greater extent, allowing your delts to take over and reducing the stress on your pecs. Keep your chest up and your shoulders back by eliminating that reaching motion at the top of the movement”. This statement contradicts itself since the delts and pecs have the same function in pressing actions. Bringing your shoulders (and arms) forward involves greater involvement of both the pectoralis major and anterior deltoid. In fact, the more you can raise the shoulders at the top of the movement the more you will involve the inner portion of the pectoralis major muscles. Reaching up at the top of the movement is beneficial for total pectoral development. It should also be noted that the back muscles are not involved in this exercise. Their role here is to help control the movement with an eccentric contraction. The pecs and anterior deltoid do all the concentric work and as a result, get most of the development. Simply referring to most anatomy or kinesiology books will give you to the answer as to which muscles are typically involved in such movements. See Biomechanics and Kinesiology of Exercise for more information.