You definitely can but with a caveat:, it so wildly depends on the muscle.
First off, there is a huge difference between
ISOLATING a certain muscle or part of a muscle and
EMPHASIZING part of a muscle.
- Isolating is cutting out other muscles and only working that one
muscle group, (notice I didn't say part of a muscle).
Little semantic tangent: Let me be straight up in saying that "emphasizing" isn't really an industry standard term. It is something I personally like and think is valuable to use to express the difference between isolation and exercises that "focus" more on a specific "head" or "part" of a muscle.
- So, with that,
emphasizing is using exercises that apply a greater amount of force to a certain part of the muscle than others, usually in an attempt to strengthen or grow that specific part more than others.
Really it all comes down to anatomy:
This comes down to the insertion and the origin point of a muscle. Remember geometry?
Two points can make a line! This line is the line that this particular muscle contracts along. It does not go in different directions.
Let's define origin and insertion because I am sure a lot of people don't know the difference:
-
Origin: this is the point where the muscle's tendon attaches to a more stationary bone (i.e., one that doesn't move during muscle contraction). The muscle contracts
toward the origin.
- Insertion: this is the point where the muscle's tendon attaches to a movable bone. It is the opposite of end of the origin.
An easy example: you can't work your biceps sideways. That doesn't even make any sense. The bicep contracts one direction, your forearm (the insertion) gets pulled towards your shoulder (the origin). The muscle contracts that way and that is the only way it ever will contract.
I see this most commonly talked about in terms of chest. which you even already mentioned in the original post
@jJjburton
First example (and one that is talked about way too much):
INNER CHEST! This simply is not
really a thing. Now, you can
try to
emphasize this part of the pec via mind-muscle connection during dumbbell fly or presses, and that might help a little bit...but in the end it really is just going to apply the same amount of tension laterally across the entire pectoralis major muscle, simply because that is the way your muscle alignment is. Due to this, technically you are working the outer pec just as much as the inner pec. The origin goes from the sternum, upper ribs, and medial clavicle (which are the origins for your muddle, lower, and upper pec, respectively) over to the insertion at the crest of greater tubercle of the humerus (basically your upper arm).
So, INNER pec is just a bro myth, you can't isolate or, to be honest, really even emphasize the inner pec. However....you asked about different angle bench presses. This is INDEED very beneficial in two ways:
- First, you
TOTALLY can emphasize different parts of the pec muscle. Upper, middle, lower pec all have their own origin points, even though they go to the same insertion point. Because of this, when you do a decline bench, you ARE indeed
emphasizing the lower pec more and for incline you're emphasizing the upper pec--you get the point. Now, I am sure you've experienaced this: since they go to the same insertion and you can't truly
isolate them, even the decline bench still works the upper pec a little bit.
- Second, when you work these different heads/parts of various muscles at different angles, you are also working
different ancillary (secondary) muscles, this is beneficial for ensuring muscular balance, reducing weak points, enhancing symmetry, etc. For an incline bench not only are you working a different section of your pec to a much higher degree, but you are using much more delt, whereas for a decline bench you are relying less on delts, more on triceps, and also even kicking in your serratus anterior to some degree. Those are the
ancillary muscles that get involved in pretty much every lift we do.
So, inner pecs, not a thing. However, you can totally emphasize different heads or parts of muscles.
- incline, flat, decline bench
- lateral raises vs reverse fly
- tricep pushdown vs overhead tricep extension vs cable/rope pushdown, etc.
- the list goes on
So, in most cases, there is very good reason to vary your exercises for the same muscle
I am not a fan of chiropractors lol, but this is a really nicely laid oud chart showing the insertion and origin of pretty much every muscle in the body. http://www.dressenchiropractic.com/Muscle%20chart.pdf
I expect I probably wrote down something similar to what's in that youtube video. I just really hate youtube and wanted to chime in with my own info. Hopefully it helps!