Research on IGF, Growth Hormone and Insulin
Nearly every athlete knows the critical importance of growth hormone
and testosterone for stimulating gains in lean mass. However, not
many are aware of insulin's powerful anabolic effects, particularly regarding
its synergistic role in producing the body's most potent growth factor,
IGF-1 (Insulin-like Growth Factor-1), the muscle builder.
You can buy the best supplements, utilize the best training program and coaches,
but unless you control insulin you will fail repeatedly in your quest for muscle
mass. How much IGF-1 your body secretes depends on how well you manage insulin.
IGF-1 is vital for the correct glucose and protein metabolism that results in
muscle growth. IGF-1 is so potent, its presence can reverse many age-related
defects such as insulin resistance and reduced muscular force. IGF-1 exerts its
potent effects much better when insulin levels are steady.
How it Happens . . .
When humans release growth hormone from their pituitary gland (located at the
base of the brain), some goes to muscle and bone to directly initiate tissue
growth. Most GH travels to the liver, where it is destroyed
within 60-90 minutes. Before this happens the liver uses this material to
manufacture somatomedins, also called growth factors. The best studied growth
factors are IGF-I and IGF-II. One of growth hormone's main roles
is to get to the liver and trigger IGF release.
Insulin interacts with growth hormone at the liver to produce IGF-I. In
circulation, both IGF-I and IGF-II have very short lives. IGF-II is mainly
responsible for nerve growth. IGF-I exerts powerful growth effects on muscle,
however, it needs a steady supply of insulin to work. Unless you've got both
insulin and IGF circulating in the right amounts, your muscle growth will be
zero. How do we know?
Research on diabetics provided the earliest examples. Insulin-dependant
diabetics have low IGF levels and a hell of a job increasing their muscle
mass.[4,5] Diabetes is a disease of inconsistent, ineffective insulin secretion
by the pancreas. A diabetic's insulin supply is like a yo-yo, constantly going
up and down depending on how much they inject and what they eat. It's almost
impossible to keep constant. These roller coaster insulin surges kill IGF
Weight Training and IGF-1
While previous research shows conflicting results with regard to IGF-1 secretion
and exercise, recent research demonstrates that a big squirt of IGF-1 is
secreted within the first 12 minutes of intense training.
Carefully designed new research also reveals that muscles used in weight
training produce a heap of bioactive IGF-1.[10,11] In fact, IGF-1 circulates in
a "system", consisting mostly of a family of six binding proteins, free
and an acid-labile unit. These six binding proteins in blood and muscle
regulate the biological activity (usability) of IGF-1.
The very latest research on IGF-1 shows that intense weight training creates a
signal within muscle to rearrange the ratio of these binding proteins and
increase the activity and availability of IGF-1. This appears to be essential to
the growth and repair process.
The total amount of IGF-1 secreted is not as important as the rearrangement of
the IGF-1 binding protein ratios.  Heavy resistance training triggers this
rearrangement fantastically well.[11,12] Also, this modulation of the IGF-1
binding proteins to create active IGF-1 is not noticed until six to 12 hours
after training.  Interestingly, this just about the time that peak muscle
protein synthesis rates kick in. Are you starting to see the link?
Growth Hormone Release is Only the Start
. . .
To maximize IGF secretion there is a biochemical sequence of events that must be
fulfilled, and triggering GH release is the first crucial step. While some
athletes inject GH others choose the safer route and enhance its secretion
naturally via intense training, increasing sleep frequency and using
research-proven nutrients such as GABA, niacin and glutamine.
Using nutrients to spike GH levels is safe. Even the highest endogenous
consists of bound (inactive) and unbound (active) forms that keep it within
tightly regulated physiological levels. However, troubles occur for the big
boys 'n' gals that shove in large gobs of artificial GH and IGF-1.
Only precise ratios of protein-bound IGF-I and GH along with the right level of
insulin, will exert a synergistic, growth-effect on muscle. Currently, the
technology to replicate this information artificially is not yet available, even
on the black market. The bodybuilder who sticks one needle under their skin and
another in their butt, and hopes for muscle growth is kind of stupid! The body's
endocrine system is far too intricate. So do your self a big favor and don't
mess with it artificially.
Artificially bombarding the body with random shots of these drugs means the
excess has to go somewhere. The surplus binds to receptor sites in organs and
intestines. So, for every 1/8th of an inch the "drug boys" add to their arms and
shoulders, they also add a good inch to their gut via organ and intestinal
growth. The result, as seen at any pro-bodybuilding show, is not a good look.
At the moment, pro-bodybuilding is an ugly sight. Sure, the pros step on stage
massive and ripped, but now they also sport hugely distended stomachs due to
years of injecting this artificial hormone cascade. Some of them have a gut so
big you'd swear if they fell over, they'd rock themselves to sleep trying to get
Injecting growth hormone is a risky business, even in controlled clinical
therapy. Several years ago, GH research for replacement therapy among older
adults seeking that elusive fountain of youth went dreadfully wrong. The late Dr
Daniel Rudman was infamous for promoting this yuppie trend. However, more than
half his subjects had to drop out of his research due to serious side effects,
such as carpel tunnel syndrome and full-blown diabetes. The latter is more
evidence of the imbalance and strain created within the body when a single
anabolic is introduced.
Hype vs. Science
Without a steady-state insulin supply, kept within a narrow, physiological range
GH levels are quickly destroyed and the active life of IGF-I is short lived.
Steady-state insulin levels prolong the active life of IGF and GH secretion so
their powerful effects on muscle may last longer.
Natural manipulation of insulin via the diet has become the next exciting
frontier for enhancing athletic performance. The intake of key nutrients at the
correct time will keep blood insulin where it needs to be. This will promote an
optimal anabolic hormone profile that enhances nutrient transport into cells,
provides better recovery and faster adaptation to training.
Many athletes have become highly skeptical of claims made by supplement
marketers about magical pathways to muscle growth. So I'm going to provide you
with the clear-cut science on what we know about enhancing natural anabolic
hormone secretion to optimize recovery and muscle growth.
Heavy, intense weight training exercise stimulates GH and IGF secretion
fantastically. In fact, the more intense the training (in terms of overload),
the higher the concentration of active IGF-1 produced. Best of all, intense
weight training enhances the potent effects of IGF-1 in people of all ages, not
Some endocrinologists suggest that consistent training enhances the GH-IGF axis,
resulting in more powerful secretions and an accumulative effect that
accelerates adaptive changes to training.
Intensity of exercise appears to be the key factor in GH and IGF-1 secretion.
Both high intensity weight and aerobic training create effective GH and IGF-1
Heavy, eccentric weight training causes the highest increases in circulating
Advanced trainers should incorporate some negative-only work into their program.
But use this method very sparingly.
Sleep is potent stimulator of GH release and training during the day amplifies
its nocturnal secretion.
Remember that spiking GH release via sleep or supplements is useless without
enough circulating blood amino acids and insulin. To ensure you have the right
building material available, consume a slower absorbing liquid meal such as
Ny-Tro Pro-40 before sleep.
While intense training sessions increase testosterone, GH and IGF levels, they
also lower insulin levels and increase cortisol (the muscle breakdown
hormone). When ever insulin is low the life of GH-IGF secretion is short
In the next article I'll show you how to optimize your anabolic hormone profile
with nutritional science.
by Paul Cribb, B.H.Sci HMS
AST Director of Research
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4. Philips LS. Metabolism, 34:765-770,1985
5. Carroll PV, Christ ER, Umpleby AM, et al. Diabetes, 49(5):789-96,2000.
6. Zachwieja JJ, Yarasheski KE. Phys Ther. 79(1):76-82,1999.
7. Parkhouse WS, Coupland DC, Li C, Vanderhoek KJ. Mech Aging Dev.
8. Rasmussen BB, Tipton KD, Miller SL, et al. J.Appl.Physiol. 88:386-392,2000.
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