Thanks to the genius brains on this planet, we know that there are two basic muscle fiber types.
The first types of fibers are known as endurance or aerobic fibers.
And of course the other type is known as strength fibers or sometimes called anaerobic fibers.
Most people have about equal amounts of these fibers, but one may be used more than the other depending on your body.
This is why some athletes seem to be born to do a certain sport or born to lift heavy things.
But as you notice no one ever says a person was born to run fast and also be the strongest person on earth.
There are a lot of things to consider when building muscle and it's important to understand that each muscle group can vary with the amount of fiber types it has.
The endurance fibers also have the potential to grow, but not even close to the size that strength fibers can grow.
Without getting to scientific, generally we use the endurance muscles doing more than 12 reps of an exercise and use the strength fibers for anything below that.
Each athlete's body contains different ratios of muscle fibers.
This is important because no two athletes should train in the exact same way.
Basically, everyone's body is different and should be treated as such.
We know that drop sets are extremely effective because they allow you to use both types of fibers.
Having both types of fibers will allow your muscles to grow bigger because they will have the endurance to lift heavier and heavier.
And that's it! It doesn't get any more complicated than that.