Fiber Conversion (was: How to lose muscle mass)

[Guest guest]

> --- In Supertraining , " donncada_pasadena "

>donncada_pasadena@...:

>On the other hand you could let the muscle

>fiber adapt (convert to Type-I fibers, smaller by the way)

>through proper endurance training.

It was my understanding that there was no potential in vivo for

fiber conversion per se (that is Type I to II or reverse) but limited

ability for IIa to IIb or reverse. What is seen is a skewed increase

in fiber type in mixed muscle in response to demand - but not a

change in type itself. That is, if vastus med. is 60% Type II and

subjected to training to favor Type II development, that those 60%

will increase, but none of the 40% that are Type I will *become* Type

II. Thus, of the post-training muscle, now 80% of the total muscle

might appear to be Type II - but their origin was all from the

original 60% and not from any of the Type I fibers.

Is this skewed development what you mean by convert to Type I - or

if you truly mean convert, can you point me to studies where this was

seen to have occurred? I'm only familiar with experimental studies

such as extended hind-limb unloading or cross-ennervation or

externally stimulated muscles that

result in some apparent fiber conversion (and only in one direction

if I recall correctly.

Sorbo

Irvine, CA