Clenbuterol, a b2-agonist, administration results in hypertrophy of fast fibres and an increase in
the fast myosin heavy chain (MHC) composition of both fast and slow muscles. The present
study was designed to determine the phenotypic response at the single fibre level.
added to the drinking water (30 mg L)1) of adult male Wistar rats for 4 weeks. Single fibres from
the soleus muscle of control (10 rats; 555 fibres) and clenbuterol-treated (10 rats; 577 fibres) were
dissected and their MHC isoform composition was determined using sodium dodecyl sulphateï¿½??
polyacrylamide gel electrophoresis analysis.
Body, heart, and soleus weights were 9, 24, and 27%
higher in clenbuterol-treated than control rats. The mean cross-sectional areas of fast and slow/fast
hybrid fibres were 64 and 74% larger in the clenbuterol-treated than control rats, whereas the size
of the slow fibres were similar in the two groups.
Fibres from control soleus showed three MHC
patterns: pure type I (84%), pure type IIa (4%), and type I + IIa (12%) MHC. Some fibres from
clenbuterol-treated soleus showed a de novo expression of type IIx MHC resulting in the following
fibre type proportions: pure type I (62%), pure type IIa (2%), type I + IIa (26%), type I + IIa + IIx
(6%), and type IIa + IIx (1%). In those fibres containing multiple MHCs, there was a shift towards the
faster MHC isoforms after clenbuterol treatment.
These data indicate that clenbuterol results in
muscle fibre hypertrophy, stimulates a de novo expression of type IIx MHC and increases the
percentage of fibres containing multiple MHC isoforms in the rat soleus muscle. These phenotypic
changes at the single fibre level are consistent with a clenbuterol-related shift in the functional
properties of the soleus towards those observed in a faster muscle
I found plenty more where they talked about farmers using it on livestock because of its anabolic properties. I guess I should have been more descriptive, I didn't say it was going to blow you up, I just merely stated that it gains anabolic properties. I was a whole lot stronger when I used it and I had a lot more motivation/energy.