There are two terms for muscle growth. One is “hypertrophy.” Hypertrophy is the enlarging of existing muscle fibers. The other term for muscle growth is “hyperplasia.” Hyperplasia results when satellite cells on the muscle fibers are activated resulting in the growth of new muscle fibers. This could be occurring for a variety of reasons, the least of which being combating physical weakness. The majority of strength increase is the result of hypertrophy.
But, before you ever cinch up a lifting belt and wrap your hands around an Olympic bar, there is an undeniable concept you absolutely must understand and accept 100% if you want to see real gains in muscle size and strength: Muscle growth (hypertrophy) is an adaptive response to progressive gravitational stress. It’s actually considered a survival mechanism. In order to grow muscle the body must be subjected, repeatedly, to a work load it cannot accomplish with the stock muscle allotment. In order to survive that stress, it builds muscle to become stronger and adapt.
And, that is IT. Other than some kind of rogue genetic factor, there is absolutely no other reason whatsoever your body will build muscle. It will only build muscle if it needs it. Not because you want 23” arms. The opposite is also true. If you have any doubt, stick your arm in a cast for six weeks and see what’s left of it when you cut off the cast. Your job as a bodybuilder is to keep your body convinced it needs more muscle – if you want to grow. That means, doing ten easy reps and putting down the weight, isn’t going to convince your body of anything, other than the fact that you might be on vacation.
While there are a variety of training protocols you can employ, none of them is demonstratively better than another, as long as you’re stimulating the body’s adaptive response which results in muscle growth. Ultimately, personal preference usually takes precedent. That’s the easy part. The difficulty comes in the form of pain. This is because the pain you must endure to stimulate growth would make a statue of Hercules cry. The exact formula to stimulate hypertrophy is no different for one muscle group or another. It’s pretty black and white. Execute it and your muscle will grow. Sandbag and you might as well not even go to the gym.
Time under tension (TUT) + Intensity (I) = Growth Stimulus (GS), GS + Nutrients (N) = Hypertrophy (H)
In this case, the “TUT” is the number of reps and sets to which you will subject a particular body part. The “I” part is done with your brain. While the former is more recognizable and universally accepted (unless you’re doing curls in the squat rack), the latter is one of those things you have to learn to generate in the presence of searing pain, both during the workout and later when the soreness sets in. If you can scratch your head without your forearms cramping the night after your arm workout, you didn’t train your biceps intensely enough. If walking up and down stairs doesn’t make you wince and grab the hand rail two days after you trained legs, then you didn’t train them intensely enough.
The concept of generating training intensity is a wide and varied topic that can fill an entire book. So suffice to say, not too much time is going to be spent here on the subject. What I will say is a simple rule of thumb followed by most bodybuilders:
No matter how hard you think you’re training, someone else is training harder....
So when you’re straining to grind out those last couple of reps and you’re ready to quit, remember, someone else is getting theirs. So, keep pushing. That's how you grow.