drtbear1967
Musclechemistry Board Certified Member
- 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 missed a few 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. A fiber must contract 100% or not at all! Think of it like a gun. Either the trigger goes off... or it doesn't. There's no in-between.
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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 of fibril will contract on the entirety of that fiber. Remember, we can't selectively contract parts of one fiber.
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What does this mean for you? Work angles of incline/flat/decline with different rep ranges and tempos to target different fibers. You can still improve the appearance of your upper/lower chest using different exercises and angles to get a good solid squeeze and induce hypertrophy in certain regions of the pecs. 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 and have separation? You'll just have to get leaner.
