Stop Targeting Your "Inner" Chest
Magazines, Instagram posts, and those charts at the gym are all guilty of showing you how to target your "inner" chest – that highly desired pec separation on your sternum that shows a distinct canyon separating the two pectoralis major muscles.
Well, the people telling us this information missed a few 8:00 AM anatomy lectures.
To get to the bottom of this myth we have to look at the "all or nothing" principle. This human physiology principle states that once a motor neuron sends its impulse for the muscle fiber to contract, the entire fiber that's innervated by that same neuron must contract in its entirety.
In other words, a fiber must contract 100 percent or not at all! Think of it like a gun or a balloon. Either the trigger goes off... or it doesn't. The balloon pops when you stab it... or it doesn't. There's no in-between.
Take a quick look at this anatomy chart:
Notice how the fibers have an obvious line of pull all the way from the center (sternoclavicular origin) to the insertion just beneath the deltoid (intertubucular groove insertion) with no interruption. If you fire the inner chest, you fire the whole fiber. Every sarcomere (unit) of fibril will contract on the entirety of that fiber. Remember, we can't selectively contract parts of one fiber.
What Does This Mean For Your Training?
Simple! Work angles of incline, flat, and decline with different rep ranges and tempos to target different fibers. You can still improve the appearance of your upper and lower chest using different exercises and angles to get a good solid squeeze and induce hypertrophy in certain regions of the pectoralis major and minor.
Just don't expect to work the middle without working the whole fiber from a lateral to medial perspective. Want that canyon on your chest to pop? You'll just have to get leaner for it to appear to have more separation.
Unsure about this same question for other muscles? Look at an anatomy chart for the muscle in question and apply the "all or nothing" principle. The next time you see a video detailing how to target your inner chest, you can eye-roll as hard as I do.