Re: Re: Hypertrophy IIA and IIB Fibres

[Guest guest]

guskara2001@... wrote:

>

<snip>

>

> He then goes on to suggest that " power and Olympic lifting shift MHC

> expression towards IIB isoform " citing an early 1981 Staron study

> that found that 7 months of inactivity by an elite power lifter

> reduced the % of IIB fibres (53-35%). Similarly Lovind-

> (1991) found a shift toward MHC IIB with 3 months of strength

> training in soccer players.

If the Lovind- study you reference is the one I'm think it is,

the soccer players were beginning a strength training program following

the soccer season. The training volume was very low compared to what

one would suspect they performed during the season (although that was

not provided in the study). This suggests that some type of detraining

adaptations occurred, rather than training adaptations. Interesting,

Trappe et al. (2001) found that not increase in IIb fibres were seen

following a training taper in swimmers, but one could argue that their

taper was not the most conducive to seeing an increase in IIb fibres.

More data regarding BBs, PLs, and OWLs has been presented over the past

few years, all showing a decrease in IIb expression and an increase in

IIa.

> This shift toward IIB, however, represents, by far, the minority

> view, but it was confusing when I first came across it. Others have

> suggested that part of the difficulty might be because of the misuse

> of two classification systems:

>

> " frequently, fast fibers that have been distinguished using either

> mATPase-based or metabolic enzyme-based classification schemes are

> equated so that IIB equals FG and IIA equals FOG. Although a good

> correlation exists between SO and type I fibers, analysis of specific

> enzyme activity levels within mATPase-based fiber types have revealed

> an entire spectrum with large overlap, so that IIB fibers do not

> necessarily equal FG nor do IIA fibers equal FOG. "

Very true. Lieber's text provides a good discussion on fibre analysis

techniques. In addition, when discussing muscle with respect to myosin

ATPase and myosin heavy chain, one must remember that there are two

techniques used. Myosin ATPase staining of intact biopsy samples (at

different pHs) can be used to identify the I, IIa, IIb and hybrid

fibres, and then each fibre can be counted and areas measured. Sodium

dodecylsulphate polyacrylamide gel electrophoresis can be performed to

determine the relative expression of MHC I, IIa, and IIb, which

correlates well to % fibre area (Fry et al 1994). Often in discussion,

SDS-PAGE and mATPase values can be confused.

Loren Chiu

Graduate Assistant

Exercise Biochemistry Laboratory

Human Performance Laboratories

The University of Memphis