Serratus: Paying Attention To Detail
The serratus is a set of muscles, which connects the lats, pectorals, intercostals, and external obliques. The serratus muscles are occasionally called the "boxer's muscle" because it is used to extend the arm and deliver the greatest punch at the greatest reach.
The muscle originates on the surface of the upper eight or nine ribs at the side of the chest and inserts along the entire anterior length of the scapula (shoulder blade). The muscles attaching to the rib cage and the edge of the underside of the scapula assists in rotating the scapula (glenoid fossa) upward and protraction and stabilization. It counters the action of the rhomboid muscle.
When you put your arm over your head, this muscle helps to rotate the scapula up and keep it close to your rib cage. If this muscle becomes paralyzed, the scapula will wing out.
Kinesiology & Physiology
In bodybuilding, the serratus muscles are the hardest to develop, because they are not exposed until you have become lean, strong, and flexible. If you look at bodybuilders or boxers, their serratus muscles are well developed from years of hard work, dedication and focus on fitness goals.
If you're using weight training as a means of exercise, which is what this series of hubs is aimed at, you don't really need to pay attention to the serratus. They'll take care of themselves. There are a lot of shoulder, chest and tricep (such as dips) exercises that will impact on this small muscle group. It's only when you're very muscular, and very lean, and pursuing bodybuilding as a competitive sport or for developing a jaw dropping physique (be it for acting or modeling), that you should make a determined effort to hit these small but impressive muscles.
Specific ab exercises that targets the serratus are rope crunches and twisting crunches. The serratus aren't easy to train and will only show after diligent work and severe fat loss.
Dips, chest dumbbell pullovers and push-ups will also help. Close grip chins will hit lower lats and also the serratus.
Here's a few extra videos to help with developing your own serratus workout regime.