When Human Growth Hormone
(GH) was first introduced to the bodybuilding world, everyone had high
hopes. Those hopes fizzled out pretty quickly,
as bodybuilders experimented with absurdly low dosages (2iu/every other
day), necessitated by its high cost. As GH costs fell due to more
efficient manufacturing processes (i.e. it was no longer being
extracted from cadavers), bodybuilders were able to use more of it, and
subsequently began to see better results. We saw the same phenomenon
with the anabolic mediator of GH, Insulin-like Growth Factor-1, and
later with its analogue, LR3IGF-1.
Now, we’ve seen the emergence of yet another compound further down the
hormonal cascade: Mechano Growth Factor (MGH). As you probably
know, skeletal muscle responds to resistance training (or any
mechanical overload), by increasing its size (hopefully). If you
‘detrain’ that muscle (i.e. don’t use it
regularly), it atrophies and gets smaller.
Similarly, when you are in your teens and early twenties GH and IGF-1
levels are high, and as you age, those levels are lowered naturally.
And if you’ve been playing along at home, you’re probably figuring out
that GH and IGF-1 are pieces of the hormonal puzzle that result in this
muscle growth (or loss). These growth
factors are produced in the liver and other areas, but also in skeletal
tissue in response to training induced damage. Now, pay attention,
because this is the important part - growth factors produced within the
muscle as a response to resistance training likely play a major role in
repair, adaptation, hypertrophy (muscle growth), and also ageing.
Scientists have discovered that many of GH’s anabolic and regenerative
effects are actually mediated by insulin like growth
factor 1. Thus, the next logical step for bodybuilders (if bodybuilders
can be said to follow some kind of logic), was to start experimenting
with IGF-1 and later with the more potent version, LR3IGF-1.
The thing is, we now know that
IGF-1
actually exists in the body in multiple isoforms. The isoform that
seems most useful to us, differs
slightly from that which is produced in the liver (IGF-1Ea). It also
appears to be the significantly more anabolic of the two we’re looking
at here (i.e. that which is produced in the
liver vs. that which is produced in the muscle). This is because it is
hyper-sensitive to the signals produced by local muscular damage
induced by resistance training. This more anabolic isoform of IGF-1 is
called “IGF-1Ec” or mechano growth factor (MGF).
That’s right, MGF, the mysterious hormone that seems to be only
whispered in e-mails and PMs on the net, is actually just another
variant of IGF-1. Yeah, if you’ve used IGF-1 or even GH, then
technically, you’ve already been taking advantage of MGF. In
fact, if you work out with weights, you’ve been producing your own MGF
- as this particular isoform of IGF-1 is only detected in
normal muscle after mechanical stimulation (such as resistance
training). Remember, MGF is just a name for the particular type of
IGF-1 which is produced locally in the muscle as part of the anabolic
repair response to resistance training.
Here’s how it happens…
When we workout with weights, the IGF-1 gene is differentially spliced
during the body’s response to local muscular overload. First
it is spliced to produce predominantly IGF-1Ec (called the MGF splice
variant of IGF-1). This initial splicing appears to stimulate satellite
cells into activation. This in turn allows the activation of extra
undamaged nuclei required for muscle fiber growth and repair to occur.
In addition, the appearance of MGF initiates the upregulation of new
protein synthesis. After this initial and short lived burst of
splicing, IGF-1 production switches towards producing a systemic
release of IGF-1Ea from the liver, which upregulates protein synthesis
as well, but over a longer time line. This secondary release of IGF-1Ea
noticeably less anabolic than the initial release of IGF-1Ec (MGF).
It is the expression of the various IGF-1
splice variants, over the
course of the healing and regrowth phase of muscle repair, that is
responsible for a generous portion of the body’s ability to
engender growth in target tissue (which is, of course, skeletal
muscle). It would appear that the introduction of this hormone, whether
by weight training or by injection, will cause a response in the area
resulting in localized muscle growth.
But, in the end, we’re still just talking about IGF-1, just a
particular form of it…
As is often the case with the ‘hot new drug on the net’, the rabbit was
always in the hat, and the magic was
only a trick. MGF is simply a variant of something we’ve had around for
over a decade. It’s just not as sexy when we call
it “IGF-1Ec”, but regardless of what we call it, it’s still just an
isoform of IGF-1. In fact, the anabolic
actions of both IGF-1 as well as MGF are achieved by stimulating and
upregulating protein synthesis, and proliferating growth and activation
of satellite cells. Actually, this latter function of MGF is quite
important, as satellite cells are the mononucleated cells in muscle
fibers located between the sarcolemma and the basal lamina.
Proliferation and activation of these cells results in the creation of
new muscle.
And all of this leads us to the real question here, which is: “How
effective is this stuff?”
Well, most of what we have to go on presently is studies in the elderly
(which there are very few of), and studies in rodents. The
most relevant rodent data has been shown that MGF is a very potent
inducer of muscle growth when it’s introduced into the muscle
via an intramuscular injection. In fact, in one study MGF caused a 20%
increase in the weight of the injected muscle within 2 weeks! Further
investigation elucidated that this was actually due to an increase in
the size of the muscle fibers!
However, scientists are coming around to identifying the one-two-punch
of MGF with regards to both inducing satellite cell activation as well
as protein synthesis as clearly showing an advantage over other types
of (systemic, or liver derived) IGF-1. In fact, when locally produced
IGF-1 was compared to systemic IGF-1 (i.e. IGF-1Ea vs. IGF-1Ec) in
later rodent studies, the superiority of the locally produced IGF-1
variants (MGF) were clearly elucidated.
It may just be that overexpression of MGF (IGF-1Ec) and the subsequent
overexpression of IGF-1Ea are the deciding factors in whether a muscle
will grow or not. But remember what I told you at the beginning about
GH and
IGF-1
in general? Until the prices on MGF go down to affordable levels,
bodybuilders are probably going to be using substandard doses of MGF
and reporting substandard results; or using tiny amounts with
boatloads of other pharmaceuticals, and claiming absurd results. In the
end, what we’re looking at is another variant of IGF-1,
that’s probably going to be even better than LR3IGF-1 at producing
muscle growth - once somebody finds a way to produce it at
affordable prices.