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.

Sincerely,
Anthony Roberts
iSteroids.com

June 03, 2006

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