Insulin and Muscle Growth

There’s been a quite a few articles written about the anabolic effects of insulin in various magazines over the last few years and with good reason. Manipulating this “anabolic” hormone and making it work for you is critical to muscle growth. Nothing really substantial occurs without it. Insulin is the anabolic activator.

By reading this and the previous article, Precision Supplement Timing – Part 4, you will be rewarded with possessing the most up-to-date, state-of-the-art research on how to build slabs of drug free muscle. This type of knowledge will help you to transform your physique. I guarantee you will not find this information anywhere else in the world. No one has put all the pieces together – until now.

Instead of going through a whole internal anabolic and hormonal physiology lecture, I’ll sum up the action of insulin in a few sentences. Then I’ll present you with the latest information that explains, in simple terms, the intricate mechanics of this incredibly potent muscle building hormone. I’ll show you how to make insulin work for you so you can take your physique beyond your greatest expectations. Best of all, it’s backed by science. See for yourself.

Many bodybuilders and other athletes choose to use external sources of insulin in their chemical arsenal of supplements – yes they inject it. Exogenous insulin is completely undetectable by current drug testing procedures. If I were shooting for a gold medal and all that goes with winning it, I might (I said might) see the logic. However, death by exogenous insulin induced hypoglycaemic coma isn’t really appealing to me, especially when manipulating your body’s own insulin levels is remarkably easy, safe, and an extremely effective way of accelerating muscle growth.

What Does Insulin Do?

Insulin is a protein peptide hormone (around 50 odd amino acids linked in an exact sequence) secreted by the pancreas. It is secreted in response to ingestion of food. Different foods evoke different blood insulin levels. The job of insulin is to transport/drive nutrients into the cells of all organs in the body, including muscle and body fat. While considerable progress has been made in the understanding of how insulin exerts its affects on muscle, after 75 years of intense research, this is basically all we know! 1,4

It is difficult to determine precisely what effects insulin has on muscle in vivo (within the living body) because it also triggers a cascade of anabolic hormonal activity and other processes that, in turn, promote potent anabolic mechanisms within muscle. Also, the intrinsic biology of insulin and its related growth factors (such as IGF-I) dictates they possess the ability to bind to each other’s cell membrane receptors and that a hybrid of interchangeable IGF/insulin receptors also exist in muscle cells.4

However, it has been well known for a long time that insulin plays a major role in regulation of protein body mass. Prior to its clinical availability, patients with Type I diabetes experienced continuous loss of protein from all tissues until they died. After its introduction it was apparent that treating of these patients with insulin dramatically restored muscle mass.4 Now as we discuss protein and muscle metabolism, it is important to keep in mind that both protein synthesis and degradation proceed simultaneously at all times. And that net protein metabolism (muscle gain or loss) is regulated by a increase/decrease of either or both of these processes.4

The Muscle Building Mechanisms of Insulin.

Recent human invivo research has revealed that insulin exerts its dramatic anabolic effect by inhibiting muscle breakdown/degradation and not stimulation of protein synthesis as invito (isolated cell cultures ) studies once indicated.1,4,7,8 (This is an important point, remember this as we will apply it later.) This process is believed to occur by the inhibition of the ubqitin-proteasome pathway (one of three major muscle degradation pathways in muscle cells). But once again, little is known about the cellular mechanisms by which insulin exerts this anti-catabolic action (just another example of how complex human physiology really is!) However, research does show that the introduction of insulin stops muscle breakdown (proteolysis) dead in its tracks and reduces net protein loss to zero.8 Also, while insulin is driving amino acids and glucose into muscle cells, it appears it also prevents the “leaking out” of these nutrients from the muscle cells that usually occur in response to training or illness.1.7,8

The presence of insulin locks in all the vital components of muscle growth.1.7,8 Kinetic studies using amino acid tracers confirm insulin is a potent amino acid transporter. In the presence of insulin, blood plasma levels of amino acids disappear. They are being driven into the cell and thus little is detected in the blood.1,4,8 However, as soon as insulin is taken away, blood plasma amino acid levels increase fast!1,4,8 They are being sucked out of muscles and utilized by other organs to meet their ravenous metabolic demands. When this is happening it is physiologically impossible for muscle protein deposition to occur! Muscle will not grow! Absence of insulin or allowing insulin levels to drop is the fastest, easiest way to induce muscle protein breakdown (catabolism). Let me explain how this relates to your training.

Research I presented in previous articles (Case for Precision Supplement Timing) demonstrates the catabolic response to weight training is so great it may equal or even surpass anabolic (muscle building) mechanisms and produce net zero gains in muscle mass. Therefore, directly after training you are in potential trouble. You must get insulin levels up quickly to counteract the enormous protein degradation that will and does occur. Recent research reviews demonstrate that an optimal hormonal environment must be created after training for muscle deposition (muscle growth) to occur.2,3 Athletes and experts who think they are in the know about building muscle assume that just eating and drinking something after training should cover this objective. However, if you examine the literature closely you will see, as I did, there is a lot more to igniting muscle growth than that!

First, studies on insulin’s effect on accumulation of creatine in muscle reveal some important points. Insulin concentrations close to upper physiological limits (above 100Mu/l) are required to maximize creatine uptake and no less than 100 grams of simple carbohydrates must be ingested with creatine to enhance the uptake!5 And, this dose proved to be close to the limit of palitability!5 100 grams of simple carbs made into a sickly-sweet drink optimized creatine uptake into muscle cells. Yuk! That’s far sweeter and a lot more carbohydrates than your average juice or sports drink contains.

Thankfully we may not have to consume this sort of sickly concoction just to maximize cell uptake of anabolic nutrients like creatine. Recent research reviews indicate a protein/carb mix stimulates insulin and other anabolic hormones levels far greater than just carbohydrates alone.3 Unfortunately, the exact insulin levels required to stimulate maximal uptake of these nutrients is currently unknown. However, from reviewing all the reports it appears insulin levels need to be pretty damn high!1,5,8,11

Second, we know insulin dramatically stimulates inward transport of amino acids and glucose into cells, but more importantly, this is shown to be a dose dependant phenomeon.8 The higher your insulin levels are at this critical time, the more nutrients that are driven into the muscle cells! Research demonstrates that insulin, in combination with an abundance of amino acids (protein), is the way to cram these vital nutrients into cells to reach the upper limit of physiological concentrations. And when you do this, muscle building mechanisms are switched into turbo mode! (see Precision Supplement Timing – Part 4)

These two important aspects point toward the fact you may have to ingest a greater amount of simple carbohydrate after your training than you are currently using to take advantage of this potent, muscle building process. The 3 hours after training is the critical time to maximize cellular transport by elevated insulin levels. And you can actually determine how much creatine and amino acids you want in your muscle cells!

Insulin and Muscle Cell Amino Acid Transporters.

Understanding insulin’s impact on muscle cell amino acid transport reveals important information on the cellular mechanics of muscle growth. An amino acid transport system is a protein bound to the cell membrane and its enzyme. It is extremely specific and only accepts/transports the amino acid it was designed for.

There have been five amino acid transporter systems identified in skeletal muscle.6

System A (stands for the amino acid alanine) transports small amounts of neutral amino acids – particularly alanine and glycine. It is a high affinity, but low capacity transporter – not real good.

Systems S and C (stands for serine and cystine) are sodium dependant, but only moderate affinity and moderate capacity amino acid transporters.

System L (stands for leucine) handles all BCAAs and aromatic amino acid transport. It is a high affinity, high capacity transporter, however, it is not sensitive to insulin.

System Nm (stands for nitrogen) is, as far as muscle tissue goes, a highly unusual transporter. It is a sodium dependent, low affinity and high capacity transporter. These qualities make it the fastest amino acid transporter in muscle and it is responsible for producing dramatic concentration gradients between the muscle cell and extracellular fluid.10,11,12 This system is the amino acid glutamine’s exclusive transporter. Most important, system Nm is highly sensitive to insulin.10,11,12
Glutamine transport into muscle cells stimulates dramatic increases in muscle cell volume. Increasing muscle cell volume (increasing the cell’s water content) is a potent, independent trigger of the anabolic mechanisms that build muscle.9 Water does not simply reside inside a cell, it must be drawn into the cell and held there by highly osmotic substrates (like glutamine and creatine) that, themselves, have high transport rates. Any imbalances of intra- and extracellular osmolarity is paralleled by respective water movement across cell membranes. This creates a subsequent cell volume alteration by either increasing or decreasing it.9

When a muscle cell increases its volume dramatic things happen – muscle growth is “turned on” and muscle breakdown is “turned off”!9 This cell volumizing process could be the important mechanism that links creatine and glutamine to their powerful, muscle building effects.

Reports demonstrate that as glutamine moves into the cell it creates rapid cell swelling. This cell swelling stimulates transport system Nm to keep increasing the rate of glutamine transport into the cell.10,11 This important finding by the scientists shows that in the presence of normal concentration of insulin, system Nm does not “down regulate” and return the cell to normal volume like other transport systems do.10,11 The cell remains in a swollen and continuous anabolic state as long as sufficient insulin levels are maintained!

The increases in cell volume we are discussing are miniscule, however, even the smallest increases in cell volume caused by glutamine trigger a potent muscle building response.12 Therefore, the unique glutamine transporter system Nm found in muscle cells appears to be a direct pathway to producing anabolism within the muscle cell and is activated dramatically by insulin.6, 11,13

Insulin Needs Amino Acids to Build Muscle

Research reviews have determined that insulin halts protein breakdown, but does little to stimulate increases in protein synthesis rates.1,4 Insulin research also demonstrates an abundant supply of amino acids must be present along with high insulin levels to produce net gains in muscle.8 In fact, the whole stimulatory effect of insulin on muscle anabolism is dependant on a large, plentiful amount of amino acids to stimulate protein synthesis rates that create increases in muscle!8 This means a rapid, easily assimilated source of amino acids must be there at precisely this time.

Since most of us can’t hook ourselves up to an IV drip immediately after training we must select our protein supplement very carefully. This protein must be absorbed and assimilated extremely fast and efficiently to be available at this time. The most superior, research proven formulation is whey oligopeptides. (More on this aspect in the next article.)

Once muscle cells are crammed with these important nutrients they have to be kept within the cell to continue to exert their powerful muscle building effects. This means two objectives have to be met. Insulin levels have to be kept constant and a continuous, easily assimilated supply of amino acids has to be present in the blood stream to meet the metabolic demands of all other organs in the body so they won’t draw them from muscle tissue! This is an important job of a protein supplement most people don’t even consider. You have to give your body the right material all the time so it doesn’t rob important nutrients from muscle tissue!

These two objectives can be easily achieved by combining protein with carbohydrate in small, very regular meal intervals throughout the day and night. However, food sources must be easily and rapidly assimilated. This is why alternating solid, fiber rich meals with Ny-Tro PRO-40 provides superior nutrient absorption kinetics that cannot be achieved with whole food sources alone. Ny-Tro PRO-40 creates a perfect foundation for muscle growth.

Ny-Tro-PRO-40 was engineered based on the outcomes of much of this research presented here. Unlike many of the “meal-replacements,” Ny-Tro PRO-40 is designed to work with and enhance the anabolic activities of specific hormonal pathways to help enhance muscle growth.

So there you have it, the nuts and bolts of insulin mechanics. It is amazing that such an incredibly complex, intricate, and potent muscle building process can be activated so easily. Armed with this knowledge and by using the right supplements, you can keep your body in an anabolic state continuously.

Step by step lets look at how this is done in a normal day’s training.

First, muscle cells must be depleted as much as possible via hard training – Max-OT .

10 minutes before finishing training, ingest a serving of Creatine HSC. Each serving has 5 grams of micronized creatine and 34 grams of carbs as well as a complete matrix of important cellular transport substrates.

Then, within 10 minutes after training introduce a large amount, approximately 75gms of simple carbs with another 5 mg serving of micronized creatine and a rapidly absorbed protein such as VP2 Whey Isolate. VP2 is absorbed and transported to the muscles within 20 minutes. It is a unique protein supplement that is designed to be utilized by your muscles more effectively than even the highest quality whey protein.

Within an hour after training eat a small solid-food protein/carb meal. This is important. If you don’t do this the valuable amino acids from your VP2 will be oxidized (burnt) as an energy source and not utilized in anabolic pathways. Don’t waste your VP2!

Then repeat step three again (with or without the creatine) within the two hour mark after training to really take advantage of this accelerated cellular uptake that is happening only during this time frame.

For the rest of the day keep insulin levels constant by alternating small low fat, meals with Ny-Tro PRO-40Ny-Tro PRO-40 and VP2 Whey Isolate (The new VyoPro Protein Bar is perfect for this) to provide superior protein absorption kinetics that cannot be achieved with whole food sources alone. You must remember calories alone do not make muscle, and dietary food sources are not equal to Ny-Tro PRO-40, VP2 Whey Isolate, or VyoPro Whey Protein in their muscle preserving abilities.
Research demonstrates that only when a specific biochemical environment is created and maintained within muscle are the muscle generating anabolic/anti-catabolic mechanisms triggered. This positive biochemical environment shifts muscle physiology towards reducing muscle protein breakdown and increasing muscle protein synthesis – growth. This ultimately influences skeletal muscle protein turnover and, because of the large mass of skeletal muscle, whole body nitrogen balance – the foundation of muscle growth.


Grizard J et al. Insulin action on skeletal muscle protein metabolism during catabolic states.Reprod.Nutr.Dev.1999;39:61-74

Kraemer WJ, et al. Effects of heavy resistance training on hormonal response patterns in younger vs. older men. 1999. J.Appl.Physiol.87(3):982-992.

Kreider RB. Dietary supplements and the promotion of muscle growth with resistance exercise.1999.Sports Med 27(2):97-110.

Miers WR and Barrett EJ. The role of insulin and other hormones in the regulation of amino acid and protein metabolism in humans. Journal of Basic Clin Physiol & Pharm. 1998. Vol 9 #2-4:235-253.

Steenge GR, Lambourne J, Casey A, Macdonald IA, and Greenhaff PL. Stimulatory effect of insulin on creatine accumulation in human skeletal muscle. Am.J.Physiol. 1998. 275;38:E974-E979

Rennie MJ. Influence of exercise on protein and amino acid metabolism. Handbook of Physiology,Section 12 Exercise: Regulation and integration of multiple systems. Oxford, UK: University Press.1996:995-1035

Takala TO, et al. Insulin action on heart and skeletal muscle glucose uptake in weight lifters and endurance athletes.1999. Am.J.Physiol.276;39:E706-E7

Zhang X, Chinkes DL, Wolf S,E and Wolfe RR. Insulin but not growth hormone stimulates protein anabolism in skin wound and muscle. Am.J.Physiol.1999.276;39:E712-E720.

D.Haussinger et al. 1998 Functional significance of cell volume regulatory mechanisms. Phys. Rev.vol78.#1.p247-290

S.Y.Low et al. Signaling elements involved in amino acid transport reponses to altered muscle cell volume. FASEBJ. 1997 vol11.p1111-1117.

S.Y.Low et al. Intergrin and cytoskeletal involvement in signaling cell volume to glutamine changes in cell volume. J.Physiol.1998 vol512 #2 p481-485.

S.Y.Low et al. Response of glutamine transport in cultured rat skeletal muscle to osmotically induced changes in cell volume. J.Physiol.1996 vol492 #3 p877-885.

M.J.Rennie et al.Glutamine metabolism and transport in skeletal muscle and heart and their clinical relevance. J.Nutr.1996 vol126 p1142S-1149S

Leave a comment

Leave a Comment