Can difference in muscle fiber types be actually physically seen if muscle being cut and put under microscope? Muscle fibers will not look the same for sure (size, color, etc), because of their different capacity of motor neurons, mitochondria and capillaries, etc. But does this give a right to separate muscle fibers into types?
As we know: If muscle is stimulated in particular way (growth or endurance training) - organism will adapt by raising or lowering the number of mitochondria, capillaries or motor neurons in order to perform in given specific external challenges. Hence, if you need more power to lift more weight - body has to grow muscle size, in order to do that it needs fast muscle contraction, which is achieved with bigger impulse coming from motor neurons. That's why it starts to add more motor neurons (hopefully it increases size as well). On the other side (for endurance training), body requires more oxygen, which comes with capacity of capillaries, myoglobin and mitochondria. Mitochondria also provides energy/ATP.
Therefore, there are but one muscle fiber, which change because of required adaptation. It is just that capacity of all functional important parts of organism affect it's shape and color of appearance. In this case created TYPES of muscle fibers (I, IIa, IIb, IIx) are there just for easier theoretical navigation, like 2+2, or is it not? Like Type IIa muscle fiber is in-between type I and type IIb. But what if muscle fiber is in-between type IIb and type IIa, or even somewhere higher or lower (if you know what i mean here). Then there can be type IIc, IId... and on. Thus, because of the wide spectrum of available capacity levels there can be many more muscle fiber types. Or is it not?
This is only my thinking and opinion. I would like you to correct me or prove me if I am wrong. As I am not sure to 100% here.