MUSCLE GROWTHupdate
By Michael J. Rudolph, Ph.D.
Senior Science Editor66 MD musculardevelopment.com July 2019
Although clenbuterol has the extraordinary capability
to stimulate fat loss while supporting muscle growth,
clenbuterol directly increases myostatin levels—
which may drive substantial muscle loss.
Clenbuterol is a popular drug used by
bodybuilders and athletes that belongs to a
class of compounds known as beta-agonists
that bind to the beta-adrenergic receptor
embedded in the cell membrane— turning
on cellular signaling cascades within the fat
cell that break down body fat while in the
muscle cell and activating muscle growth.
These functions bestow clenbuterol with the
extraordinary capability to decrease body fat
while supporting muscle growth. Although
clenbuterol is a powerful bodybuilding
compound, it also has several drawbacks.
One of those drawbacks being the rapid
inhibition of clenbuterol activity within the cell
that swift ly shuts down its fat-burning and
muscle-building activity. In addition, scientifi c
evidence has shown that clenbuterol not only
loses its anabolic potency rather quickly— but
it may also stimulate muscle atrophy if taken
for extensive periods of time, by increasing
the amount of the muscle-depleting molecule
myostatin within the muscle cell.
Myostatin is a member of the transforming
growth factor-beta (TGF-beta) super family of
growth factors where, despite being a growth
factor, it actually reduces muscle growth by
initiating several pathways that inhibit muscle
hypertrophy while stimulating muscle atrophy.
However, certain nutritional supplements have
been shown to inhibit myostatin activity , which
should prevent clenbuterol-stimulated muscle
loss while enhancing clenbuterol-driven muscle
growth. In addition, these myostatin-inhibiting
compounds should also lower the amount
of clenbuterol necessary for muscle growth,
which would also diminish cellular inhibition of
clenbuterol within the cell— further enhancing
the anabolic properties of clenbuterol.
REDUCING MYOSTATIN ENHANCES
CLENBUTEROL’S ANABOLIC ACTIVITY
One key investigation clearly demonstrated
that inhibiting myostatin function improved
clenbuterol activity. This study by Kim et al.^1
showed that clenbuterol, which has previously
been shown to enhance muscle size via the
mTOR pathway^2 , works well in combination
with myostatin inhibition to additively stimulate
muscle growth and strength. The researchers
took normal mice and myostatin-defi cient
mice and fed them clenbuterol. Aft er two
specialreportCLENBUTEROL
Cuts Both Ways
weeks, muscle biopsies revealed an additive
eff ect on mTOR activation in the myostatin-
defi cient mice that were also fed clenbuterol.
These myostatin-defi cient mice that were fed
clenbuterol had an increase in muscle mass
of ~25 percent. The result of this investigation
demonstrates that inhibiting myostatin clearly
enhances clenbuterol function.CLENBUTEROL AMPLIFIES THE LEVEL
OF MUSCLE-DEPLETING MYOSTATIN
Considering the previously mentioned study
by Kim et al.^1 which showed that clenbuterolstimulates greater muscle growth when
combined with myostatin inhibition, another
study by Abo et al.^3 investigated whether this
inhibitory function of myostatin on clenbuterol
was induced by clenbuterol consumption. In
this study, researchers analyzed the level
and activity of myostatin in the muscle of
rats that were given clenbuterol for 21 days
straight. Muscle hypertrophy was induced
from day three to 14, which corresponded to
increased levels of the muscle-building growth
factor IGF1. In addition, the study also showed
increased levels and activity of myostatin