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For years the three Staples of chest development I have known have been upper pecs, middle pecs, and lower pecs. There are a lot of posts about inner and outer oec development.. and even a lot of information from classic bodybuilders such as Schwarzenegger. My question is.. can these actually be trained and if so should they even be a focus? I do a three day workout a week so my exercises are the big compound movements without a lot of extra isolation exercises like flyes or cable crossovers. I thought I also remember in some medical journals that there's no such thing as outer or inner pecs.. outer pecs are really part of your lower pecs and inner pecs are part of the middle.

If these are necessary to train, how can I tell if I am lacking in one? I know too much development in lower pecs look like breasts, and too much in middle makes your chest jut out.. but how can I tell if I'm missing inner or outer?

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    With all due respect to Mr. S and the bodybuilders of his era, many (if not all) of them used steroids, and the science has advanced enough in the last 40-50 to date a lot of his advice/theories. The pec major is one muscle with two heads, everything else such as shape is genetics. You can't activate just "part" of a muscle. That being said, there are definitely good split routines to give a full development based on the head location and the pec minor. – JohnP Feb 10 at 14:37
  • I agree and that goes along with some people who think you can't train the outside or the inside of a quad based on mechanics. But I have seen a lot of beginner bodybuilders look like they have breasts rather than full round pecs and Arnold was able to apparently even target the left and right sections of his calf. I do incline presses, close grip, and flat bench for the most part. I rotate decline bench press for flat on occasion – Ace Cabbie Feb 10 at 17:56
  • Arnold and so on did marathon training sessions almost every day of the week, 3 hours + of calves, forearms and all sorts of weird stuff. It's true that the body builders of that era had great looking bodies, but they also dedicated much more time to the gym than the average Joe can. I don't know if you can train the inner pecs a bit more by performing certain movements, but you can certainly waste your time in the gym. Even if you have 2 hours 5 times a week to spare, you will hardly have the time to get to this bonus stuff. Beginners often overlook one key factor: Efficiency – Raditz_35 Feb 10 at 19:56
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If we understand the function of a muscle, that muscle certainly can be trained. Indeed, if a muscle has a function, performing that function is training the muscle. So the question is whether there exists such a thing as ‘inner’ and ‘outer’ pectoralis muscles, and if so, what their function is.

To be clear, there is strictly no such thing as inner and outer pectoralis muscles. That is, the lateral and medial portions of the muscles are comprised of the same fascicles, and hence the tension in those muscle fibres is consistent across their length during contraction. There are no medial and lateral fibres because the fibres of the muscle do not run vertically. So by definition, we cannot train the lateral and medial portion of the muscle separately.

However, it is possible that the terms ‘inner’ and ‘outer’ are misnomers for the anatomical terms deep and superficial, in which case we would be referring to the pectoralis minor and pectoralis major, respectively. The terms ‘lower’, ‘middle’, and ‘upper’ refer to the general alignment of the muscle fibres of the pectoralis major, with the latter term normally being made in reference to the clavicular portion of the muscle, (illustrated below).

Pectoralis major muscle

Although the two muscles are geographically adjacent, they have broadly different functions. The pectoralis major acts principally as a prime mover, and is dominant in climbing, pressing, and throwing movements. The pectoralis minor, by contrast, primarily acts as a stabiliser, depressing and protracting the scapula. Thus, the action of the former invariably involves the latter.

For bodybuilding, a knowledge of the precise action and function of a muscle can help us isolate it in training. And whilst it is not possible to separate these muscles entirely—their lines-of-pull are too closely associated—we can reduce the function of one in order to focus on the other.

The pectoralis major has its origin at the anterior surface of the medial half of the clavicle (clavicular head, or ‘upper’ pectorals) and the anterior surface of the sternum and superior costal cartilages (sternocostal head, or ‘middle’ and ‘lower’ pectorals). It then inserts at the lateral lip of the bicipital groove of the humerus. This means that if we adduct and internally rotate the humerus, and if we depress the shoulder girdle, the pectoralis major will approach a state similar to that of active insufficiency, being unable to produce force because of the length-tension relationship. (It cannot strictly be called active insufficiency, since the pectoralis major is not a multi-joint muscle.) Thus, this condition will allow greater contribution from the pectoralis minor, which inserts on the coracoid process of the scapula, and whose action is to depress and protract the shoulder girdle. Pre-fatiguing the pectoralis major will further place emphasis on the minor.

Since the pectoralis minor is not functionally a prime mover, no gross functional movement will target it specifically. However, if we are creative, we can devise exercises that might help. Shoulder depression repetitions from a arms-down, pronated-grip position on the bar would be one way to do this.

I hope that gives you a starting point.

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There are two pecs - minor and major. Lower, middle, and upper refers to parts of later one - pectoralis major. Pectoralis minor is attached to scapula, and moves shoulders down, and froward. I would rather train back, and stretch this muscles - to have proper posture. We spend too much time sitting in position that makes them shorter.

When you are climbing pectoralis minor, and coracobrachialis can be useful, from time when we ware spending time at trees... Or at least that is the only case came to my mind.

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