You can work on a muscle to change its mass but its shape will be determined by your genetics.
I have worked out 4 to 6 times a week ever since I was 16 (I am now 30). Overall I am happy with my physique. However, one spot that has always given me trouble is my chest.
The problem is the shape. It peaks pretty well in the center but I have never had much luck building the lower sides of the pecks (i.e. where the peck meets the external oblique). Ideally, I would like an even distribution of muscle mass ranging from the center of the chest out to the sides (i.e. square in shape).
Does anyone have any pointers on how to build and shape the lower / outer chest muscles?
You can work on a muscle to change its mass but its shape will be determined by your genetics.
I kind of figured that would be the case. I will just work on bulking it up and see what the results are. I'll be honest. I probably do not concentrate on my chest as much as I could be doing.
Thanks.

Decline presses and wider dips on parallel bars can help carve out that lower/outer line in the chest and build size (but considering you've been lifting for a long time, you probably already know that). As previously mentioned, genetics will determine shape but there's still ways to make the most of what you've got. Gaining more size in certain areas can help accentuate them/make them more pronounced.
Thanks all for the pointers. Although I have been lifting since high school, I have never really investigated much into the correct way to do it. Yes, I've been around gyms enough to know all the different exercises out there and the importance of keeping good form and having a well rounded work out.
Personally, I think my biggest problem is that I have never really accomplished a concentrated work out. I am so worried about working out everything that nothing really gets focused on. As such, I have done a great job keeping myself fit with descent tone. However, I have always lacked bulk and highly defined muscles (i.e. large, defined arms and a square chest).
I found this article pretty informative about how to possibly build my arms:
Direct Assault: The “Case” for Arms Training | Mind and Muscle
However, I am not sure if there is much other then a concentrated work out that will give me a better defined chest (i.e. I most likely just need to work it out harder and really focus on my form ... such as more of a squeeze when I get to the top). I just thought that, like the arm article alludes to, oftentimes there are muscle groups around or under other muscle groups that, if built, will accent the muscle group you want built. In my case this would be the lower part and sides of the peck.
Thanks again for the help.

I was merely suggesting, if he wanted to hit the lower/outer pecs, that he should do specific exercises to hammer them and make the most of what his genetic capabilities will allow. And when I mentioned 'certain areas', I meant the whole muscle, rather than, say, a section of it. Apologies if I wasn't clear. My bad.
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