Targeting the inside or outside of a muscle. Can you train the inner chest, lower biceps etc.?
How can I train my inner chest?
Good question. And unfortunately, even "certified" trainers will tell you that you can. Well, no you cannot! That's due in part to the fact that many (MOST) trainers lack any real experience, education, or even tangible results for that matter.
It's impossible to train one "end" of a muscle above another. People ask me every day (really, almost every day!) "how can I work the lower part of my biceps?". My response is always the same- you can't. The biceps are so named because it's a muscle with two distinct heads. Just as the triceps have three heads, and the quadriceps four. No matter what type of biceps curl you do; incline dumbbell, preacher, spider curl, standing barbell curl, supinating dumbbell curl, concentration curl or double cable curls; one thing, and one thin only happens to the biceps- they shorten on the concentric phase of the movement. The biceps pull. In fact, every movement is a pulling movement. Muscles DO NOT push- EVER. Pushing motions are performed when a muscle pulls.
This doesn't mean that we cannot try to better isolate one head over another, or a muscle within the same "group".
A simple example that demonstrates exactly what I'm talking about: If I attach a rope to a ceiling joist, and a weight to the other end- when I allow the weight to hang- there's exactly the same force exerted across the entire rope. No more at the top, bottom, nor middle. That's pretty much common sense, but that figure of speech is a misnomer.
This point only holds true for the attachments of the muscles being trained. The pectorals are trained at different angles for a very good reason. We can concentrate slightly more force on the pectoralis minor during a decline press or a cable crossover. It holds true for all of the more complex muscle groups. Foot position, angles, pronation or supination of the hands, hand or foot width (grip or stance width) all affect the muscles differently.
So, next time someone tells you "they're training their inner chest" or any of the other nonsense flying around out there, please consider that muscles have attachments, and it's impossible to exert more force on one attachment over another. If your "trainer" does this, fire them immediately!
The way your muscles, or mine grow on one end to another is purely genetic
Some important clarification!
While you cannot stimulate one end of a muscle more than the other, you can design a program that shifts influence on different heads of muscle groups- even when they sdhare common attachments.
Pronation or supination of the hands will influence, the pectorals, biceps, triceps, deltoids, or latissimus dorsi. If you take into account the biceps are the group that turn the hands inward or outward, it becomes obvious that hand position matters. Full supination at the top of a biceps curl exerts the most contractile force on the biceps.
Triceps: Pronating the hand at the bottom of the pressdown will fully contract the long head of the triceps. Supination of the hands will involve the outer two heads slightly more.
The deltoids: Pronation will shift influence to the medial and posterior heads of the deltoids. This is why it's important to turn the pinky upward at the top of a side lateral or bent side lateral raise. So all of you using the EZ curl bar with your pinky down for the upright row, get a clue! At best, if you are going to use the EZ curl bar for upright rows, the pinky should be at the top of the camber!
Latissimus dorsi: Reverse grip (supinated) rows or pulldowns allow the elbow to travel downward and outward the most. This better contracts the lats and involves more lower lat.
Pectorals: Supinating the hands at the top of a cable crossover shifts influence to the upper pectorals.
Where the legs are concerned, a toe out stance or posture involves more adductors in the squat, hack squat or leg press. This does far less than most people think where the calf raise is concerned. It's the position of the knee (straight or bent) that influences the gastocnemius over the soleus. Seated calf raises (knees bent) are better suited to targeting the gastrocs than standing. Again, the reverse is true here.