Re: Re: Strength, Endurance & Muscle Fibres

[Guest guest]

Loren Chiu wrote:

> (...) If we look at myosin ATPase staining,

> > we see that with resistance training (...) , there is an

> > increase in the number of type IIa fibres and a decrease in the

> number

> > of type IIb fibres... However, greater type IIa fibre area has been

> > correlated to higher rate of force development (unpublished data,

> to be

> > presented at the 2001 NSCA conference). Type IIa fibres are also

> > associated with greater weightlifting and vertical jump performance.

Éric Lépine wrote:

> Wow! I wasn't aware of that Loren. I always thought that high

> intensity resistance training geared towards increasing power would

> increase or at least favor development of type IIb fibres, not IIa.

> I also never imagined that type IIa fibers were associated with

> greater weightlifting and vertical jump performance (you mean more so

> than type IIb or do you simply mean to say that a greater proportion

> of IIa and IIb in general is better than someone with a high

> percentage of type I with either type IIa or IIb???)

Muscle biopsies of top US national level weightlifters showed a very

small percentage of IIb fibres, moderate percentage of I fibres, and

high percentage of IIa fibres (either through myosin ATPase staining or

MHC analysis through gel electrophoresis). Correlations comparing % MHC

IIa fibre area and weightlifting and VJ performance were highly

positive.

Most studies have shown that a IIb --> IIa shift occurs regardless of

training program, except two studies by Saltin (maybe others?). In one,

no fibre type shift was seen in sprinters, and in the other, a IIa -->

IIb shift was seen in soccer players. I have only glanced at these

articles so will avoid further comment on them. However, IIb fibres are

called " couch potato " fibres as they seem to be present (at a high

percentage) in untrained individuals only. We don't know why the shift

occurs since in vitro, the IIb fibres are faster. Unfortunately,

adaptations to training are not a high priority of " pure " muscle

physiologists, and the number of " applied " muscle physiologists around

is not very high.

Regarding power type training, there is some evidence that the myosin

light chains (particularly the essential light chains) may play an

important role chronic adaptations to this type of training, however,

other than some recent work by Trappe, I am unaware of much research

regarding MLC adaptations to training.

Loren Chiu

Graduate Assistant

Exercise Biochemistry Laboratory

Human Performance Laboratories

The University of Memphis