The “Pec” Major

The Mighty Pectoralis Major

The mighty pectoralis major. I think no muscle symbolizes the male body builder more. This is probably so because there is no natural way that the pec major becomes so overdeveloped. Now that I am into CrossFit, it's all about functional now. But what's functional about the pectoralis? You literally need a strong back and strong legs to do work, but strong pecs? Maybe only if you're lying down and refridgerator falls on you would you need to bench press 350lbs. Large pec majors are only for those body building types who want to show off. At least that is what I tell my underdeveloped chest and is the reason why I want a bigger chest.

That means that I will need to work out all the pectoralis muscles right? If there is major muscle there must be a minor and the pecs are no exception. Except for the fact that the pec minor is just tiny muscle only seen on autopsy. It is located well beneath the fan shaped pec major and it's only function is to subtly tilt the scapula downward. It is a stabilizer muscle and far from a "show muscle." No matter how hard you work it you won't be able to see this muscle unless its larger brother is stripped away. The upper chest sometimes referred to as the "pec minor" is just the superior-most aspect of the pectoralis major.

But let's return the discussion to function. What is the function of the pectorals? Well to see the function you must see the structure. The pec major is fan shaped muscle with its origin or proximal attachment from the clavicle all the way down the sternum to the upper abdominals. The fibers then all converge on the upper humerus as pictured below. Interestingly the fibers twist so the the inferior ones attache above or superior to the upper fibers stretching from the clavicle. This gives each aspect of the pectoralis muscle a different function. When the upper fibers contract it will lift the humerus in a flexion motion and when the lower fibers contract it will bring the upper arm back down to midline known as adduction. In general, when all the fiber contract the arms will cross in front of the body. What makes this interesting in regards to exercise is that there are multiple planes of motion in which the pectoralis functions. It doesn't have just one job. This is reflected in its innervation. Each pec has six motor units, allowing different part of the muscle to contract independently by the nervous system.

By knowing this my fascination with the pectoralis has grown. I still think that huge pecs are just "show muscles" (i.e. they show that you spend way too much time at the gym doing exercises that translate little to real life), but they have an interesting story to tell on their own. Don't peg them as just bench press muscles. They are essential for shoulder flexion and arm adduction and if you want to work them out properly you're going to have to do it in multiple planes of motion. These guys have six separate muscle groups that fire independently of one another. Just one exercise is not going to do it!