My professor at school believes that you can train your type IIb fibers and actually train to increase your type IIb. He acknowledges that aerobics and endurance training results in IIb-IIa shifts, but denies the fact that all types of training seem to increase the type IIa fibers.
I need some help. I’ve looked up several studies on isoform conversions and adaptations with humans and rats, and he still doesn’t believe me. He says that the subjects in the studies aren’t training intensely enough and that’s why they shift to IIa.
He also denies the fact that sedentary and older people have more Type IIb than many trained athletes.
I have two questions:
It is well known that Type IIb fibers are the largest and have a potential for great growth, so at what point are these fibers converting to Type IIa? It seems like these IIb fibers are hypertrophied and then are converted to a bigger version of Type IIa fibers a couple weeks later?
When researchers take biopsies are they looking at a Type IIb that has the mitochondrial density and enzymatic capabilites of Type IIa, or are they looking at a fiber that is identical to the IIa without any trace of ever being a Type IIb?
My professor insist that it only looks like there's more IIa fibers, because they have hypertrophied and take up more CSA, in reality the same type IIb fibers are still there unchanged.
Can someone with more firsthand knowledge than me explain this clearly so that I can pass it on to my out of touch professor. Thanks!