Take the abdominal muscles as an example:

Genes determine how many ABS you have.

The division of rectus abdominis is determined by genes.

As far as abdominal muscles are concerned, the number of abdominal muscles depends on individual genes. You can have 8 abdominal muscles without hard training. If you are born with only six ABS, you can't have eight ABS even if you practice ABS every day. Including the shape of abdominal muscles, the asymmetry of abdominal muscles, whether it is strip or block is determined by genes!

Don't question your training method because of the shape of abdominal muscles. In fact, these are innate and cannot be changed and adjusted!

The upper limit of muscle growth cannot be changed.

The final size of muscle depends on the size of bone.

It is much easier for people with big skeletons to practice to 45, but it is much more difficult to practice to 45 with small skeletons.

This is not to deny that you can't practice much if your skeleton is small. Theoretically, people with big skeletons have a bigger upper limit of muscle growth!

Muscle growth rate cannot be changed.

The speed of muscle growth depends largely on the level of testosterone. Take friends you know in the gym or friends who train around you. Some of them want to gain muscle easily, some train hard in the gym every day, their diet keeps increasing, and their muscle growth rate is very slow. This is the effect of their testosterone level.