Intermittent Thoughts on Building Muscle: IGF-1, TNF-α, IL-15 & Co and the Emerging Role of an Auto-/Endocrine-Immune Axis in Skeletal Muscle Hypertrophy

Image 1: The word "inflammation" triggers associations which hinder a appropriate understanding of the complexities of the "inflammatory" immune response that is vitally important for (re-)building muscle tissue.

Just to make sure that I do not get off another tangent, again, I will start right off, where I left you in the last installment of the Intermittent Thoughts and that was with the promise to have a closer look at the intricate relationship of (exercise-induced) inflammation and the increases in muscle-specific insulin-like growth factor 1 (IGF-1) and its splice variants, above all the muscle (re-)building mechano-growth factor 1 (MGF-1). Before we are looking how one influences the other, we will yet have to establish a consistent understanding of "inflammation", which, despite being in on everyone's lips these days is commonly (mis-)understood and / or confused with "oxidation", as in the oxidation of "inflammable" substances, you have encountered innumerable times in the form of fire or rust.

What is inflammation? And is it good or bad?

If we simply rely on our everyday understanding of inflammation, we are totally missing the boat on the true significance of a very complex net of biological processes some scientists quite blunderingly labeled "inflammation", which is not the "fire", i.e. the damaging (in many, but by no means all cases oxidative) process, itself, but the appropriate, or, as in the case of auto-immune reactions, inappropriate physiological reaction to it. Whether this misleadingly termed reaction of your immune cells is "appropriate" and thusly healthy or "inappropriate" and thusly detrimental, depends on a whole host of factors, among which the distinction between subclinical chronic inflammation and acute inflammatory responses probably is the most important one.

Illustration 1: The theoretical relationship between the biphasic hormetic curve and exercise salience (Nunn. 2010. Fig. 1)

While scientists believe that a chronic low, yet elevated level of inflammation is the root cause of almost all modern disease, the acute inflammatory response to real threads is the driving force behind those hormetic adaptation processes about which Alistair V. Nunn and his colleagues from Imperial College in London write that their "decline [...] in our daily life may be leading to increased systemic sub-clinical inflammatory tone, decreased metabolic flexibility and suppression of exercise salience" and thusly set the stage for "obesity, the metabolic syndrome, diabetes, vascular disease and even cancer" (Nunn. 2010). It is thusly only consistent of the researchers to demand:

Whether we like it or not, a long and healthy life needs to include regular exposure to occasional doses of environmental stressors, including fasting, natural temperature changes, polyphenols and exercise. Although human intelligence has enabled us to remove most stressors from the environment, common sense may be required to re-introduce some of them.

And while I could unquestionable go into much more detail on the concept of hormesis and its fundamental importance to our health, I am determined not to lose sight of the real intention of this installment of the Intermittent Thoughts, which is to elucidate the intricate relationship between the local inflammatory response to exercise, the intramuscular expression of IGF-1 and its splice variants and the exercise-induced increases in skeletal muscle mass and strength.

The IGF-1 response to acute inflammation

Contrary to what you may have gathered from a cursory read of the literature on the "dangers" of the "growth promoting" and thusly potentially carcinogenic insulin-like growth factor, neither the mature 70 amino acid polypeptide IGF-1 nor any of its splice variants are in and out of themselves carcinogenic. It is the (not even indiscriminate, cf. red box) growth promoting effect they exert on target tissues via interactions with the respective IGF-1 receptors which will promote the growth and proliferation of all sorts of cells, including cancer cells that is responsible for their bad reputation.

Image 2: IGF-1 per se is not fattening,
if anything it is "IGF-resistance"

Did you know that a 2008 study by a group of scientists from the University of Leipzig, in Germany, found that the "growth promoting" effect of IGF-1 on adipocytes is negligable, the effect of the latter on systemic IGF-1 expression via negative feedback, on the other hand pretty profound (Klöting. 2008)? As it turned out, not IGF-1, but its absence, or I should say, its inability to activate the receptor in the IGF-R knock-out mice that were used in the study were the underlying cause of both statistically significant increases in body, fat and organ weight, as well as ~20% elevated serum IGF-1 levels. Similar to the fattening effects of insulin, its structural cousin (cf. insulin vs. insulin-like growth factor discussion in the previous installment), it is thusly not the physiological expression of IGF-1, but its inability to trigger necessary cellular signaling cascades and negative feedback that could be at the heart of the metabolic derrangements that oftentimes go hand in hand with elevated levels of circulating IGF-1.

In this context an important result of a meta-study by Claudio Franceschi and his colleagueson genes involved in the etiology of longevity, comes to mind (Franceschi. 2005):

In a longitudinal survey it has recently been shown that older women having low serum levels of IGF-I and high serum levels of IL-6 have the highest risk of disability and mortality, in comparison with women who have low levels of IL-6 and high levels of IGF-1 (Cappola et al., 2003). Such a beneficial effect of high IGF-1 serum level in the elderly is in apparent contrast with the above reported data showing that reduced IGF-I plasma levels are associated with longevity (Bonafè et al., 2003b). In order to reconcile this apparent discrepancy, it can be hypothesised that the decrease in plasma IGF-1 observed in nonagenarians and centenarians might minimise the risk of cancer in these subjects by decreasing a generalised mitogenic stimulation. The price to pay is frailty and massive reduction of muscle strength, two characteristics of such very old people.

With this connection between overexpression of the inflammatory cytokine interleukine 6 (IL-6) and the low, or as we will see insufficient IGF-1 expression in elderly people, we have come full-circle and back to our initial question: How do "inflammation" and IGF-1 expression go together?

Image 3: Unlike Hermes, the Greek messenger of the Gods, cytokines have no intrinsically mischievous side and their vilification is unjust.

Although it was certainly not a good idea to summarize such a complex phenomenon as the release of signaling molecules and the consequent reponse of the immune system under the term "inflammation", the name "cytokine" is actually quite fitting, because the combination of the Greek words -cyto, for "cell", and -kinos, for "movement", denote the exact consequences the release of respective signaling molecules has: it induces the movement of cells, which, in the case of "inflammatory cytokines", obviously are immune cells. The contemporary vilification of all "inflammatory" cytokines in the lay-press is however unwarranted - or would you hold the guy who takes the calls on the emergency line responsible for either the outbreak of the fire (=immune reaction necessary) or another nuisance alarm (unwanted auto-immune reaction)?

A very important clue that points us into the right direction comes from a 2007 study by Pelosi et al. (Pelosi. 2007), who analyzed the regenerative process skeletal muscle tissue undergoes subsequent to injuries. The scientists analyzed the differential expression of the two major inflammatory cytokines TNF-alpha and IL-1-beta, which in turn triggers the release of the aforementioned (and much better known) IL-6 in skeletal muscle (Luo. 2003), in response to cartiotoxin (CTX) injection in normal (wild-type) mice and mice who were genetically engineered to over-express mIGF-1 specifically in differentiated myofibres (MLC/mIGF-1).

Figure 1: Differential expression (relative to maximum) of TNF-alpha and IL-1b in CTX-injected muscle of wild-type and MLC/IGF-1 mice during the 10 days of recovery (data adapted from Pelosi. 2007)

As the data in figure 1 goes to show, the higher mIGF-1 expression (the "m-" indicates autocrine production, i.e. IGF-1 that is produced right at the target tissue, in this case skeletal muscle) in the genetically engineered mice led to a statistically significant amelioration in the expression of pro-inflammatory cytokines, which are involved in the recruitment of monocytes and macrophages.

An "anomaly" you will probably have noticed is the sudden increase of both inflammatory marker on day 5 post injury. I don't know if you are familiar with the term "deep onset muscle soreness", but the "onset" increase in inflammation certainly reminds me of the feeling I tend to have whenever I have gone overboard on squatting. Do you know what I am talking about? This awkward feeling of cramping pain in the quads that tends to appear right then, when you thought that the soreness was abating? Interestingly enough, this sudden onset of inflammation, which is completely absent in the MLC/mIGF1 mice, goes hand in hand with a the peak of  another, less well-known cytokine that goes by the (telling) name of macrophage migration inhibition factor, or MIF. This stands in contrast to the MIF response in the MLC/mIGF-1 mice, where

the significant down-regulation of MIF at 5 days post-CTX injection in MLC/mIGF-1 injured muscle may facilitate the emigration of infiltrating cell pools, leading to a rapid resolution of the inflammatory response.

These facilitatory, or rather dis-inhibiting effects IGF-1 seems to exert with respect to the MIF-driven "lockout" of the macrophages, allows for a "rapid restoration of injured mIGF-1 transgenic muscle", of which Pelosi et al found that it...

was also associated with connective tissue remodeling and a rapid recovery of functional properties.

Show that autocrine mIGF1 via its modulating effect on the inflammatory response and its (related) ability to reduce the formation of fibrotic muscle tissue "creates a qualitatively different environment for sustaining more efficient muscle regeneration and repair" (Pelosi. 2007).

Image 4: The local administration of platelet (and growth factor) rich plasma is about to become a recognized treatment strategy for muscular injuries and chronic degenerative joint diseases such as tendinopathy.

Did you know that a 2006 study from the University of Melbourne showed that both, IGF-1 gene transfer to the injured muscle (which would be comparable to the autocrine mIGF-1 expression discussed in the previous paragraph), as well as systemic IGF-1 administration via mini-osmotic pump at 1.5 mg/kg/day "hastened functional recovery" in artificially injured tibialis anterior muscles of mice? The injection of platelet rich plasma, which contains various growth factors, into injured muscle tissue is already practiced by many physicians working with competitive athletes (Creany. 2007) and appears to be a promising treatment strategy for other (non-muscular) pathologies such as chronic degenerative tendinopathy, as well (Vos. 2010).

If we set these results into a somewhat broader context, it becoms clear that the inflammatory cytokines that are released as a result of muscular damage, summon macrophages and other immune cells to the injured tissue. The concomitant production of local mIGF-1 facilitates their migration into the muscle where they increase the proliferation of satellite cells (Merly. 1999) and help (re-)building (new) muscle tissue (Chazaud. 2003). The "ameliorative" effect of IGF-1 on inflammation is thusly by no means comparable to the "ameliorative" effect firefighters exert on a fire. IGF-1 does not work against the inflammatory response (remember: in 99% of all cases the latter is a completely healthy and beneficial physiological reaction to an external assault on your body!), it works hand in hand with the driving forces of "inflammation", the monocytes, by "opening the door to the muscle" and rejuvenating the satellite cell pool from which, in turn, relies on the immune cells during the incorporation of these progenitor cells into the existing muscle tissue.

The emerging importance of an endocrine-immune-axis in skeletal muscle hypertrophy

Image 5: Control (A) and IL-15 treated (B) myotubes; nuclei are stained yellow; note the wide myotubes in the IL-15 treated muscle (img. from Quinn. 2002)

This intricate interplay of the endocrine (IGF) and the immune (monocytes) system, which is so characteristic for our emerging understand of the true complexity of the mammalian physiology, reminds me of the question Trevor's Facebook question from last week. Trevor, who has obviously done his homework on the "IGF-1 / cytokine connection" wanted to know my thoughts on interleukin-15, one of the less-researched "inflammatory" cytokines, which appears to play a central role in the accrual of myosin heavy chain (MHC) motor proteins (if you have not done so, already you can read more about the role of the motor proteins in Part II of the Hypertrophy 101). Back in 1995, already, a group of scientists from the American Lake VA Medical Center published a ground-breaking (yet hitherto unfortunately largely overlooked) paper on the role of interleukin-15 in skeletal muscle myogenesis (Quinn. 1995). Quinn et al. were for the first time able to show that

IL-15 used at concentrations of 10 or 100 ng/ml increased MHC accumulation five-fold in C2 myoblast cultures and 2.5-fold in primary bovine myogenic cultures. Moreover, C2 myotubes formed in the presence of IL-15 appeared larger than controls.

Interestingly, the researchers must have apprehended the existence of the previously discussed intreaction of the endocrine and the immune system and tested whether this effect depended on the presence of IGF-1:

Figure 2: Moysin heavy chain expression (arbitrary units) in in bovine muscle cultures after incubation with IL-15 (dose in ng/ml), IGF-1 (dose in ng/ml) or both (data adapted from Quinn. 1995).

From the data in figure 2 it becomes quite obvious that IL-15 has more than a facilitative effect on the IGF-1 induced accrual of motor proteins. A 2002 follow up study on mice myocytes (Quinn. 2002) and a 2003 study using human skeletal muscle myogenic cultures (Quinn. 2003) confirmed the validity of these initial findings.

Figure 3: Myosin heavy chain expression, protein synthesis and protein degradation in rodent muscle in response to IL-15 treatment at different basal levels of IGF-1 (data adapted from Quinn. 2002)

Interestingly, the synergistic effect of IL-15 and IGF-1 appears to be restricted to the accrual of motor proteins (cf. figure 3) and has only marginal effects on protein synthesis and degradation.

mTOR & Co, IGF-1, inflammation ... what's next?

Image 6: Is the role of naturally achievable testosterone levels in the accrual of lean muscle tissue overrated, or not? What exactly does the principal male androgen do on a tissue level and why did your OTC test booster only increase your libido and not the size of your sleeves?  Come back on 01.01.2012 to learn more ;-)

With protein synthesis and degradation, we have come back to one of the initial discussed cornerstones of skeletal muscle hypertrophy (cf. What is Hypertrophy?), of which you should have learned in the previous installment of this series that is a necessary, yet not sufficient prerequisite of sustainable muscle growth. Without the IGF-1 mediated and, as you have learned in this installment, monocyte-driven (re-)construction (increase in myonuclei + accumulation of motor proteins) of the underlying structure of the muscle, however, neither the repair of damaged, nor the accrual new, functional (cf. Hypertophy 101: Part II) muscle tissue would be possible.

The question we still have to answer before we can eventually integrate all those different pathways into a model which would allow us to develop a "hypertrophy-optimized" training, nutrition and supplementation regimen, we do yet still have to shed some light on the role of the legendary "big T": Testosterone! So stick with me and come back next week, or next year, whatever you like better, to learn more about the actual role of the principal male sex in the complex process of skeletal muscle growth.

Intermittent Thoughts on Building Muscle: IGF-1 and its Splice Variants MGF, IGF-IEa & Co - Master Regulators or a Bunch of Cogs in the Wheel of Muscle Hypertrophy?

Image 1: With regard to IGF-1 and its splice-variants like MGF, there is probably 10x-100x more bro- than pro-scientific data out there - this does not help us, though, since you never know which of the bro-reports is bogus and which is not.

In view of the fact that we have not covered much ground with the last installment (we did build a pretty solid foundation, though ;-), I will try my very best to steer a middle course between presenting impressive amounts of facts and explaining the complex and in part not even completely elucidated physiological underpinnings of skeletal muscle hypertrophy, or, as the bros would say, getting big and buffed! A pros pros Bro, you will unquestionably have read on one of the myriads of bodybuilding-related bulletin boards how the injection of X amounts of IGF-1 right into the muscle made BigGuns, or whatever the poster's pseudonym may have been, grow "3 inches in 2 weeks"... ok, his profile picture looks impressive, but is that credible? Does IGF-1 really have such profound effects on muscle growth? And about what type of growth are we talking here? The myostatin-negative "ballooning up" of the muscle, which leaves you with overblown myogenic domains and dysfunctional muscles?

IGF-1: Insulin, growth hormone, or what?

To be able to answer these and related question we will first have to understand what exactly this "insulin-like growth factor 1" actually is. From a (bio-)chemical perspective it is nothing but a bond of 70 amino acids which are entangled into a specific peptide structure that is characteristic for somatomedin C, as IGF-1 is also called. Both the "growth" in IGF-1, as well as the "somato" in its old-fashioned appellation already suggest that what we are dealing with, here, is a "growth hormone related" polypeptide. And in fact, the synthesis of IFG-1, which, in the case of the systemically available fraction, takes place primarily in the liver, and is triggered by systemic growth hormone (somatotropin) levels.

Figure 1: Changes in systemic IGF-1 levels after 5-weeks on either a "normal" (=55:15:30 carbs:protein:fats) or a low carb "high protein" (=20:30:50) diet in 8 men with untreated type II diabetes (data adapted from Nuttal. 2006)

The "insulin" in its name, however, is pretty misleading... or I should say people mislead themselves, by not reading  the name correctly: It's not "insulin-growth factor", but "insulin-like growth factor" and the "like" refers to the structure of the molecule and does not imply that it is released in response to insulin spikes, as you may have read it on one of the aforementioned bulletin boards. If you do take a look at the growth hormone and IGF-1 levels of eight male subjects in a 2006 study on the metabolic of 5-weeks on what the scientists call a "high protein, low carbohydrate diet" (Nuttall. 2006), you will see that an increase in protein and fat from 15% to 30% and 30% to 50%, respectively elicited an 34% increase in serum IGF-1 levels over the treatment period, a finding that is corroborated by the recently published results of Matthew B. Cooke and his colleages from the Department of Health, Human Recreation and Performance at Baylor University.

Figure 2: Serum IGF-1 levels in response to whey vs. maltodextrin supplementation and subsequent lower body resistance training (data adapted from Cooke. 2011)

In their randomized double-blinded cross-over study, Cooke et al. had a group of 10 recreationally active men (2-3 non-resistance training exercise sessions per week) perform a lower body exercise program (leg presses and knee extensions, 4 sets, 8-10 reps at 80% of the individual 1RM) with either 10g of maltodextrose or 10g of whey 30 minutes before the exercise bout (Cooke. 2011). The results of the study (equal IGF-1 response regardless of whey or carbohydrate supplementation) imply that even in the short term, in healthy subjects and in conjunction with exercise the ingestion of carbohydrates is not superior to the provision of fast acting protein sources as a means to either increase or maintain systemic IGF-1 levels.

On a side note: The insulin-mediated induction of Akt, which subsequently triggers the phosphorylation of the mammalian target of rapamycin (mTOR) and thusly does its bit to elevate protein synthesis, has no direct relation to IGF-1, which - I cannot emphasize that enough - has a structure resemblance to insulin, nothing more, nothing less. And what's more, the insulin response in the aforementioned study by Cooke et al. was identical in the whey vs. maltodextrin arm of the study.

Systemic vs. local IGF-1 expression: A crucial distinction

If you have been following the daily research updates here at the SuppVersity over the last months, you may now be wondering why I am even caring about those growth hormones (after all you should, after reading the first paragraph, realize that IGF-1 is something like the active incarnation of somatotropin), when Stuart Phillips lab has quite conclusively shown that even the exercise induced elevation of testosterone does not correlate with subsequent increases in muscle protein synthesis. Certainly a good question, but nevertheless not difficult to answer:

1. The previous installments of the Hypertrophy 101 (Part 1, Part 2) should have made it quite clear that protein synthesis alone is not sufficient to grow. Without intra-muscular restructuring / reorganization and the recruitement of new myonuclei from satellite cells, you would sooner or later grow beyond the maximally allowed myonuclear domain sizes (assuming that by whatever means you block the healthy upregulation of mystatin that will prevent that) and end up as an over-muscled but completely dysfunctional wrack.
2. In a very recently published study, the results of which I have actually been holding back, because I thought I would get to them much earlier in this series, the very same Stuart Phillips whose studies are "responsible" (in fact it is the way they are discussed by the lay-press and abused by the supp-companies that is actually "responsible") for the current over-emphasis on acute increases in the protein synthetic response to exercise and/or supplements, reports that there actually was a statistically significant correlation between exercise induced growth hormone release and increases in mean type I fiber (p<0.06) and type II (p<0.04) cross-sectional area (CSA) in 56 healthy previously non-resistance trained healthy young men in response to a 12-week, 5-day per week resistance training regimen (West & Phillips. 2011).
3. While we have hitherto been talking about systemic IGF-1, it has become evident in the course of the last decade that the hepatic IGF-1 output, which is the main determinant of circulating IGF-1 levels, has little to no impact on the IGF-1 induced increases in skeletal muscle mass and remodeling of muscle tissue that has been previously studies in Petri dishes. In fact, recent research suggests that, just like the liver produces IGF-1 for "the whole body", muscles produce their own IGF-1, or I should say, their own IGFs-1, whenever they are challenged to grow and/or repair (Velloso. 2010), and that the decline of muscle mass with age is at least in parts attributable to a defect / reduction in the expression of local IGF-1 splice variants (for an explanation of what this is, see red box below).

If we now count 2. and 3. together the result is not 5. but rather that it is the growth hormone mediated, exercised-induced local expression of IGF-1 splice variants, which drives the repair and restructuring process that allows for continuous (healthy) muscle growth.

Did you know that the intra-muscular (=autocrine, meaning directly in the tissue where it is supposed to work) "construction process" of the mature 70 amino acid polypeptide IGF-1 gives rise to three different splice variants of insulin-like growth factor (note: the structure of IGF-1 gene does theoretically allow for 6 variants)? And though we are just beginning to understand the physiological roles of IGF-IEa, IGF-IEb and IGF-IEc, also known as MGF (mechano-growth factor), their distinctly timed expression in response to physical overload appears to constitute one of the major driving forces of myocellular hypertophy.

In order to fully understand the role "the" insulin-like growth factor 1 plays in the physiology of muscle growth, it is thusly important to realize that the common perception of IGF-1 as a systemic hormone is, at best, incomplete - I would even venture to say that it is totally flawed.

MGF?! Yeah, I have heard of that one!

Figure 3: Stained myocyte migration (top) and infiltration (bottom) essays for IGF-1 and MGF; more stains = greater effect (taken from Mills. 2007).

Of the three primary splice variants that are expressed in skeletal muscle, IGF-IEc, or MGF (Mechano-Growth Factor) has probably received the greatest attention - so much attention that even the aforementioned bros, will probably have grasped the notion that this is somewhat of a local isoform of IGF-1 which is expressed in response to exercise induced muscle damage and could potentially be the magic bullet to grow beyond what we have hitherto believed to be possible... and, guess what, in essence this appears to be correct.

In one of the earlier studies on the cellular effect of MGF, Yang et al. were able to show that MGF stops the IGF-1 mediated cell differentiation process (in practice this means that it stops the satellite cells from differentiating = specializing and becoming muscle cells) and increases their proliferation. Or put more simply: While in vitro exposition to IGF would suffice to build muscle, as long as there are enough progenitor cells (satellite cells) available, MGF is necessary to replenishes the satellite cell pool of which you have learned in the previous installments that it is necessary to a) repair damaged muscle tissue and b) increase the number of myonuclei in order to grow beyond the physiological growth limit that arises due to the muscle-type-specific upper limit to the myonuclear domain size (cf. previous installments).

Figure 4: Cell proliferation data in response to MGF treatment after blocking the IGF-I receptor.

As the data in figure 4 goes to show the effects of the complete polypeptide IGF-1 and its splice variant MGF appear to be mediated, at least partly via distinct receptors. And while recent research suggest that MGF also exerts similar effects on tendon (Olesen. 2006), brain (Dluzniewska. 2005) and nervous tissue (Aperghis. 2004), our primary concern here, is its pivotal role in muscle repair, which involves the activation of satellite cells, their proliferation (Yang. 2002) and migration (Mills. 2007).

A series of studies by Hammad et al., which was originally intended to investigate the effects of age on the expression of the different IGF splice variants, goes to show that the "muscle (re-)building effects" of MGF are not restricted to the test tube. In their 2002 study (Hamed. 2002), the researchers were able to show profound increases in the MGF expression in the quadriceps muscles of 8 healthy young men (age 29.5 ± 1.5 years, body mass 81.1 ± 2.4 kg, height 179.3 ± 1.8 cm) 2.5h after a single muscle-damaging leg-extension exercise (10 sets of 6 repetitions at 80% 1-RM, 2 min rest between sets):

Figure 5: MGF (ng mRNA / 10^8 µg RNA) and IGF-IEa ng mRNA / 10^5 µg RNA) expresion in quadriceps muscle of young subjects before and 2.5h after 10 sets of 6 repetitions at 80% 1-RM on a leg-extension machine with 2min rest between sets (data adapted from Hamed. 2002)

If you take a closer look at the data in figure, you will probably notice that there was one subject with an extreme MGF response, the scientists explain by a particularly high type-IIx fiber content of the quadriceps of this individual. If you remember the mouse studies and the analysis of the muscle composition of bodybuilders from the previous installments, you will be aware that the shift from type IIb to type IIx muscle fibers is one of the main characteristics of "getting real big". The extreme MGF response (>10x higher than the mean MGF expression across the other subjects) in this subject thusly suggests the increased growth capacity of type IIx muscle fibers is in part due to their ability to release MGF in response to strenuous exercise and thusly multiply / replenish their satellite cell pool to prepare for future growth.

Figure 6: MGF (ng mRNA / 10^8 µg RNA) and IGF-IEa ng mRNA / 10^5 µg RNA) expresion in quadriceps muscle of young subjects after eccentric HIIT exercise on cycle ergometer (data adapted from Hamed. 2008)

Interestingly, a 2008 follow up study (this time involving nine healthy young men aged 20–27 years, cf. Hamed. 2008) with a completely different training protocol that consisted of

60min of opposing the rotation of the pedals down to 60 r.p.m. Subjects performed the following program of six working intervals: six working intervals: 0–6min at 50%, 6–12min at 75%, 12–20min at 100%, 20–25min at 130%, 25–40min at 100% and 40–60min at 75% of the load  eliciting concentric VO2max

illicited surprisingly similar results (cf. figure 6). And in both cases, it appears to be the MGF splice variant not the IGF-IEa variety that drives the short term (hours to days) response to strenuous exercise.

HIIT and resistance training a dynamic duo for MGF expression

Assuming that you are following each and every post here at the SuppVersity (you know you should be ;-), this should remind you of a previous blogpost of mine (cf. "HIT Your Satellite Cells to Increase Your Gains!"), in which I explained that one of the many advantages of high intensity training (not even interval) over classic "cardio" training is that it can increase satellite cell proliferation. Now, with this installment of the Intermittent Thoughts you finally understand, why this is the case.

Image 2: This is not the kind of muscle damage you should be aiming for in the gym.

Now, while protein synthesis and increases in domain size are partly mediated via nutrition, the intra-muscular expression of the IGF-IE splice variants appears (at least based on the current research) to depend solely on exercise, or I should say the wear and tear that goes hand in hand with heavy exercise. In that it seems to be less important, whether you are "pumping away" or "cycling like maniac", as long as its "hard" - to put that into perspective, in the 2008 study by Hamed et al. the subjects underwent ~3600 eccentric muscle contractions in only 1 h, their creatine kinase (CK) levels (marker of muscle damage) increased by +183% and all subjects reported profound muscle soreness.

This controlled amount of muscle damage ties in nicely with the topic of next week's installment which will center around the the intricate relation of the inflammatory response to exercise, the expression of the well-known and less known inflammatory cytokines, TNF-alpha, IL-6 and IL-15 (sorry, Trevor, I have already gone overtime, so your question will have to wait till next week ;-) and the muscle (re-)building effects of IGF-1 and its intra-muscular children.

Intermittent Thoughts on Building Muscle: The Skeletal Muscle Hypertrophy 101 - Part 2: Getting Big Means Growing Beyond Temporary Physiological Limits.

Image 1: This is another type of "dysfunctional muscle"; distinct from the one we are talking about, here

Although I assume that you all have read the last installment of the Intermittent Thoughts, I took FatFree's comment that he (or she?) was missing the "too comlicated check box" from the old design to the heart (I do so with every comment, btw, so keep them coming) and kick off today's installment of "The Thoughts" with a brief and even more "dumbed down" summary of what we have learned about the (possibly) ascertained and, even if human skeletal muscle hyperplasia existed, dominant factors in the trinity of skeletal muscle growth: Protein synthestic increases in myonuclear domain sizes and the satellite cell driven incorporation of new myonuclei.

Getting big goes beyond ballooning up

You probably will remember the balloon-metaphor, I introduced in the red infobox toward the end of the last installment. Let's briefly get back to that and use it to reavaluate the results from the Quaisar study (Qaisar. 2011, see also "What is Hypertrophy"). Rizwan Qaisar and his colleagues from the Uppsala University in Sweden had analyzed the differential effect of insulin-like growth factor 1 (IGF1) over- and myostatin-underexpression on muscular size and function (the latter is important, since we know that a complete lack of the "muscle growth blocker" myostatin leads to huge, but disfunctional / weak muscles). 

Figure 1: Domain sizes of EDL and soleus muscle fibers in wild-type control, myostatin negative and IGF1 overexpressing mice (data based on Qaisar. 2011)

Now to really understand the meaning of what may be the main message of the study, it is imperative to understand the basic architecture of muscle fibers. If you think about a complete muscle fiber as a bundle of ballons that is wrapped into a strechable net, then each balloon would represent one myonuclear domain. The owe their name to the fact that they actually are the "domains" which surrounding a single myonucleus (lat. plural "myonuclei") within a given skeletal myocyte, which - contrary to other cells in your body - has the ability to hold multiple nuclei. Now, the most obvious determinant of the myonuclear domain size is the ratio of protein in- to protein efflux. And it is this connection on which researchers base their belief that by simply measuring the protein synthetic response to exercise and/or supplementation would suffice to predict long-term increases in muscle size (and subsequently strength / performance).

Growth is limited and myostatin is not just a pain in the ass of anyone who wants to "get big"

Image 2: Sketch of a mammalian skeletal muscle fiber - myonucleus (turqouis), mitochondria (blue),  sarcoplasmic rectilium (buff), tubules (orange), myofibrils (pinkish)  - Artist: Lesley Skeates. Originally from Gray's Anatomy 29th ed. Elsevier. 2008

If you take another look at the data from the Qaisar study (cf. figure 1), you will notice that uncontrolled growth in "one dimension", i.e. exclusive increases in domain size, generates larger muscles, but at the same time renders them dysfunctional, a process of which Qaisar and his colleagues believe that it is caused by a decrease in the number of strongly attached cross-bridges, which are the primary source of the small specific force in muscle fibers with very large MNDs. This hypothesis is by the way supported by a lowered myosin (contractive motor-protein) content per muscle volume in the myostatin negative mice.

In order to really understand why this is the case, it may help if you take a look at the (awesome) sketch of a mammalian skeletal muscle fiber on the right (image 2). The myonuclei are colored in turquois-green, they are connected to the mitochondrion (blue) and the sarcoplasmic rectilium (buff), which is traversed by transverse tubules (orange, and not easy to distinguish). The major part of the muscle fiber is yet made up by myofibrils, which are protein chains containing actin, myosin, and titin...

Ah... wtf. Before someone wants to click the "too complicated"-button again, let's just say the myofibrils are the ones who do the actual work. Now, with the increased domain size (obviously the domain is the "zone" comprising all the aforementioned components that a single nucleus is "responsible" for) and the consequent decrease in myosin content (per volume), as well as the reduced number / density of cross-bridges, i.e. links between the myofibrils to coordinate their action, the muscle loses its functionality. Just like a labor brigade with 5 smaller, smart guys who listen precicely to what their foreman says and work hand in hand can get the job done more efficiently than 5 big, but dump guys, who do not even listen to what their foreman tells them, this type of one-dimensional growth, i.e. an exclusive increase in domain sizes, goes at the expense of muscle function.

From satellite cells to broadcasting towers and back again

Image 3: Myonuclei have a domain, similar to the broadcasting area of a transmitter mast.

So, the myonuclear domain, has nothing to do with some sort of "fenced off" area that is protected by a cell membrane. In physics, we would probably talk about a field, a field of influence, just like an electromagnetic field, with the exception that the signalling from the nucleus does not work via EM radiation, but via gene-signalling... mTOR & Co says hello ;-) Satellite cell recruitment and the "installation" of new myonuclei would thusly be equal to the installation of new broadcasting towers, which make the existing system more effective and allow for further expansion. If you are a mobile communications veteran, who knows the "good" (or rather bad) old days of poor reception you'll know what I mean.

In this context it may be interesting that a very recent study by Antonios Matsakas et al. was able to show that the voluntary wheel running or swimming was able to restore the function of the "over-blown" muscle of myostatin-null (MSTN-) mice (Matsakas. 2011). Another clear cut evidence that exercise induces structural changes which go well beyond the accrual of protein that is not adequately controlled in the MSTN- mice.

Do you take my point now? Ok, then let's get on...

The expression of myostatin, which prevents the myonuclear domains from further expansion is thusly a means by which your body maintains muscular function. Contrary to my friend Adelfo, your body has no interest in looking like Phil Heath... the only reason it has to grow is to be able to survive and survival requires functional strength, not size. There is yet some leeway as far as increase in domain sizes are concerned and it is this leeway that explains the "exorbitant" gains you have been making when you first hit the gym. The lazy bastard (sorry ;-) you have been before, your myonuclear domains were probably far beyond their "functional" limit and, consequent to the acute protein synthetic response to your 1001 biceps curls, "ballooned up" until, just as Darryn S. Willoughby observed it in his 2004 study (Willoughby. 2004), the contemporary increase in skeletal muscle myostatin content brought the expansion of the "bloated" myonuclear domains to an "abrupt halt" (at least that was probably your perception).

Figure 2: Relative myofibrillar protein content and myostatin mRNA expression in the thigh muscles of 11 previously untrained subjects in response to a 12-week (3x per week) resistance training regimen with 3 sets of leg presses and knee extensions à 6-8 reps @85-95% of the 1RM (data calculated based on Willoughby. 2004)

As the relative amount of myofibrillar protein content and myostatin mRNA expression in skeletal muscle from the previously 22 untrained male subjects of the Willoughby study shows (cf. figure 2), the myofibrillar protein accretion is accompanied by profound increases in the expression of muscular myostatin. Or, put simply, the bodies of the subjects, whose thigh volume increase by roughly 16% in the course of the 12-week study period, were sensing that without structural changes, this type of muscle growth would eventually lead to huge, yet dysfunctional muscle fibers - something that obviously would not promote survival and is thusly not part of our genetic program.

Structural changes facilitate new growth

On the other hand, the constant overload to which (I hope) you are exposing yourself in the gym signals your body that without increasing strength (again, your body does not care about size), it will not last much longer is the "adverse environment" of the gym. So, the only way to "survive" is to rebuild / restructure the muscles, a process of which we have seen in the last installment of this series that it goes hand in hand with decreases in the number of purported hypertrophy prone "ultra-fast" twitch type IIb muscle fibers (or rather the content of respective myosin heavy chains within your muscles). Whether the resulting phenotype is that of a bodybuilder, characterized by increases in both the number and size of slow-twitch type I and fast-twitch (intermediate) type II-x fibers, or that of a powerlifter, characterized mainly by increases in the number and size of (intermediate) type II-x fibers, depends on the training stimulus, alone:

Image 4: Our bodies respond to different training routines by distinct changes in the muscular structure.

• Wanna get strong like a German Olympic gold medalist Matthias Steiner? Then goto the gym, 10x a day and do a 1-rep max plus minimal auxiliary work like people the Bulgarian O-lifters are supposed to do. 
• Wanna get big like Arnold? Then follow his example and break into your local gym on Sunday (Arnold's was not open 24/7 back in the day, but that did not stop him from training) and pump out rep after rep, after rep to make sure your body understands that you want to maximize both type-I as well as type-II fiber size.

This does not mean that you cannot get big and strong, it does yet mean that a competitive bodybuilder will - per pound of lean body mass - always be weaker than a powerlifter.

"I need YOU!" ... to pick my brain and steer this series in the right direction

The sixty-four-thousand-dollar question now is: What is the "best" way to let your body know what you (not even your brain, but rather your mind) wants? And even at the risk that I am losing my "guru status" now, I want to be honest with you: I don't know the answer... at least not yet ;-) I thusly depend on your help, on people like Steven Acerra, who is constantly picking my brain with interesting questions and studies on facebook, Mike T Nelson, who lately jumped in on an interesting discussion on training stimuli, "Fat Free", Aaron, Matt, Erik Istre, Lerner (whose comments I have been missing lately) and all the rest of you who chime in with questions, suggestions or the simple assessment that the "good Dr. Andro" is once again making things only more complicated ;-)

And as a food for thought, I give you a sneak peak at what should come next in this series: It is the intricate relation of protein and endocrine signaling by which your muscles and no central governor or transient elevations in isolated systemic testosterone, growth hormone or insulin levels regulate the concomitant increases in muscle protein synthesis and satellite cell recruitement and changes in the myosin heavy chain composition. So, assuming that this installment of the Intermittent Thoughts did not raise further questions as far as the basics are concerned, the next installment will revolve around the role of IGF1 and its local (=intra-muscular) cousins MGF and IGF-IEa, which appear to play a key role in the the coordination of the restructuring process that will keep your muscles functional, even when you are approaching a Olympia stage ready bodybuilding physique.

Green Tea for Muscle Protection? GTE Increases Satellite Cell Proliferation & Differentiation, Slows Disuse-Related Atrophy, Does not Promote Hypertrophy in Aged Rodents

Green tea as a magical muscle preservative for injured athletes?

"GTE increased satellite cell proliferation and differentiation, decreased oxidative stress and the abundance of Bax, a proapoptotic protein" (Alway. 2014) - that's the initially exciting result of a recent study from the West Virginia University School of Medicine and Abbott Laboratories. What is not exactly as exciting, though, is how the sentence continues, i.e. "yet this did not further improve muscle recovery in reloaded muscles" (Alway. 2014).

Sounds contradictory, right? Well, before we get deeper into the discussion of the results, let's briefly recap how Alway et al. arrived at these insights, i.e. how exactly the experiment looked like and which experimental evidence it generated.

The scientists from the West Virginia University School of Medicine tested the hypothesis that green tea extract (GTE) would improve muscle recovery after reloading following disuse. In men and women "muscle disuse" would equal lying around in bed or on the sofa all day. In rodents it was simulated by an initial 14-day period of hindlimb suspension (HLS) and a subsequent period of reloading (recovery).

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The subjects the researchers use were Fischer 344 Brown Norway rats who were randomly assigned to receive either 14 days of hindlimb suspension (HLS) or 14 days of HLS, followed by normal ambulatory function for 14 days (recovery). Additional animals served as cage controls.

Figure 1: Muscle wet weight. Muscle wet weight was obtained in hindlimb muscles of cage control animals, after 14 days of hindlimb suspension group (HLS), or after 14 days of hindlimb suspension followed by 14 days of reloading (Recovery). And Ex vivo isometric force. A. Maximal tetanic force obtained at a frequency of 100Hz, or B. Peak twitch force (PT) of the plantaris muscle was measured in cage control rats, after 14 days of hindlimb suspension (HLS) or after 14 days of hindlimb suspension followed by 14 days of reloading (Recovery | Alway. 2014).

Both active treatment groups were given green tea extracts at a dosage of 50 mg/kg body weight - that's roughly 600-750mg of green tea extract per day. The control group received pure water, instead.
As you can see in Figure 1, the animals that received the green tea supplement exhibited a significantly attenuated loss of hindlimb plantaris muscle mass and tetanic force during.

In addition, compared to the vehicle treatment, GTE attenuated muscle fiber cross sectional area loss in both plantaris (-39.9% vs. -23.9%, p<0.05) and soleus (-37.2% vs. -17.6%) after HLS. This green tea-induced difference was not transient but it was maintained over the reloading period.

Increased muscle retention = increased fat loss!?

That's particularly interesting in view of the fact that the changes in body weight did not differ between the green tea and water group (see Figure 2).

Figure 3: Relative reductions in total body body weight in the two groups (Alway. 2014)

Why? Well it signifies that there is a significantly reduced negative impact on the body composition, with green tea. That does not change, though, that "GTE failed to further improve recovery of muscle function or mass as compared to vehicle treatment" (Alway. 2014)

This begs the question - would you recommend GTE? As a muscle preserver during periods, where you cannot workout, yes. The way it conserved the muscle mass in the study at hand should help help you to get back to the grind after a debilitating exercise, even if the recovery in the study at hand seemed to be identical in both groups. The green tea induced increase in satellite cell proliferation and differentiation, as well as the decreased oxidative stress and the abundance of the catabolic protien Bax, on the other hand, is probably not going to have a significant effect as long as you are still able to move, because exercise alone will induce more pronounced benefits in these domains.

Figure 4: Changes in body composition in a study w/ obese subjects comparing GTE to resistance training and a combination of both green tea extract and resistance training on body comp. (Cardoso. 2013)

Plus: We should not forget that the effects were observed in old rats and thus in a model of a population group that appears to benefit from antioxidant supplementation more than young(er) people. If you don't belong to the corresponding group of human beings whose muscles are particular prone to oxidative damage and suffer from a reduced ability to adapt to exercise induced stress, the effects remain questionable. In obese individuals green tea has yet been shown to promote the beneficial effects of exercie on body composition (Cardoso. 2013) - the risk that it a low dose of GTE does anything but good, does thus appear to be very small; and that's true for the benefits for athletes, too - at least according to previously reported results | Comment on Facebook!

References:

• Alway et al. "Green tea extract attenuates muscle loss and improves muscle function during disuse, but fails to improve muscle recovery following unloading in aged rats." Journal of Applied Physiology (2014). Ahead of print.
• Cardoso, Gabrielle Aparecida, et al. "The effects of green tea consumption and resistance training on body composition and resting metabolic rate in overweight or obese women." Journal of medicinal food 16.2 (2013): 120-127.

Sulforaphane from Cruciferous Vegetables Inhibits Myostatin and Increases Cell Viability in Skeletal Muscle Satellite Cells

Chicken Egg Rolls with Red Cabbage, Mango & Lime (CleanEatingMag); small inset shows sulforaphane content (µg/ml) of a juice made cauliflower, broccoli, red and white cabbage and brussel sprouts (based on Totušek. 2011).

When I am looking at the currently top-rated posts (see box "Most Popular (last 30 days)" on in the right navigation bar), it appears as if someone must have found my older article on the myostatin boosting effects of clenbuterol and told all his facebook friends about it.

Don't forget to check out and tell your friends about the latest SuppVersity Facebook News, as well!

In case this hypothesis is right, he (or she?) and all the friends will probably be happy to hear that there is a virtually side-effect free over-the-counter alternative that can suppress myostatin and thus make your muscles grow faster: Broccoli, cauliflower, cabbage and co (see image on the right and realize Red Cabbare, not broccoli is the King!) - the sulforaphane in these cruciferous vegetables appears to make that possible.

Muscle building veggies... yamyol!

Back in the day Popeye was invented to convince children that it would be worth eating their spinach (unfortunately this advise was based on the false assumption that it was a good source of iron and would thus help build the kids' stamina). I guess when the inventors of Popeye get wind of the soon to be published paper we are going to look at, today, we are soon going to see a digital avatar of Mr. O. munching broccoli in a 3D animated cartoon.

Sulforophane protects muscle against exercise induced damage: Although pertinent studies on the myostatin inhibiting effects of sulforophane outside of the petri dish have yet to be conducted, a rodent study from 2009 did already observe another, likely related effect of sulforophane  supplementation in intact animals. Administered at dose of 25mg/kg (human equivalent: 4mg/kg ~ 300-400mg for an average adult) it exerted significant ameliorative effects on exercise induced muscle damage (Malaguti. 2009). Against that background it does not seem to be exactly unlikely that chronic sulforophane supplementation or cruciferous vegetable consumption could give you a slight edge over those who don't eat their greens.

Whether the digital broccoli munching Mr. O Popey will be able to bring more scientifically sound arguments to the table than his predecessor, popeye does however still have to be determined. After all, the scientists from the Animal Breeding and Husbandry Group at the University of Bonn in Germany did not study the real-world effects of sulforaphane (SFN), but only the in vitro effects the exposition of porcine satellite cells to, of which every SuppVersity reader knows that they function as skeletal muscle stem cells and support muscle growth and regeneration following injury or disease, when they found that...

"[...] SFN treatment significantly represses MSTN expression, accompanied by strongly attenuated expression of negative feedback inhibitors of the MSTN signaling pathway. miRNAs targeting MSTN are not implicated in posttranscriptional regulation of MSTN." (Fan. 2012)

If you take a closer look at the data in figure you may notice that this increase in myostatin went hand in hand with a decrease in MyoD expression. With MyoD being a protein that is involved in the very first step of satellite cell recruitment (it stops the proliferation of stems cells and initiates their transformation to muscle cells) this may seem awkward at first.

In view of the MyoD promoting effects of trichostatin A, which basically stops cell development in its tracks it can however be explained by the fact that less new satellite cells are needed, because their survival is increased so that the proliferation rate does not actually suffer (figure 1, left).

Figure 1: Cell viability, proliferation, MyoD, Myostatin and (total) Follistatin mRNA expression in porcine stem cells (satellite cells) from semimembranosus muscles from 6 purebred Pietrain piglets after exposure to DMSO (control),  trichostatin A or different concentrations of sulforaphane (SFN; data based on Fan. 2012)

This explanation does not only stand in line with the previously reported increase in MyoD expression in aging muscle (in this case unfortunately in the absence of increased cell viability; Alway. 2012), but is also supported by the concomitant downregulation of the pro-apoptotic (=initiating cell death) caspase enzymes (not shown in figure 1) in the SFN treated satellite cells.

In conjunction with the decrease in myostatin, which is, as I am sure you all know the 'myocyte hypertrophy break' of your body, the data from this in vitro study clearly suggests that SFN treatment could well have a growth promoting effect on skeletal muscle, which is -- and this may be one of the most important messages here -- more prononce at lower concentration used in the study.

Figure 2: Appearance of SFN in serum (triangles) and its metabolite in the urin of one of 10 healthy, normal-weight adult (34 +/-13 y) male volunteers after the ingestion of 200g of raw (top) or cooked (bottom) as part of a warm meal (Vermeulen. 2008)

Bottom line: After you have read about the potent anti-adiposity effect of antibiotics which are used in poultry fattening, yesterday, and today's news about the myostatin inhibiting effects of cruciferous vegetables, or more precisely, their sulforphane content, the infamous 'chicken breast, broccoli and rice diet' does actually begin to shine in new splandor! I mean, if only 50% of the aforementioned in vitro effects could actually be achieved by eating like this day in and day out, these recent findings could well explain, why generations of bodybuilders thrived on these spartan foods. And in case you wondered why the guys get freakier year by year - that's simply the availability of broccoli extracts and the increased use of antibiotics in poultry fattening... ;-)

I am obviously just kidding. If we go by the bioavailability data of raw (figure 2, top) and cooked (figure 2, bottom) broccoli, 200g of broccoli served as part of a warm meal will get your blood SFN levels up to only 2.5% or 1.2% of the most effective dose (5µM) used in the study. So, it's pretty certain that you'd have to gobble copious amounts of red cabbage juice (see picture on top of the article) to get there.

In view of the fact that lower concentrations yielded greater effects, it is however not totally unlikely that even concentrations as low as 1µM would yield results. With additional supplements, it does therefore not appear to be unrealistic to achieve blood levels like that (although you should not expect the increase to be linear).... anyway, I will let you know as soon as the first pertinent rodent or even human trials are available.


References:

• Alway SE, Degens H, Lowe DA, Krishnamurthy G. Increased myogenic repressor Id mRNA and protein levels in hindlimb muscles of aged rats. Am J Physiol Regul Integr Comp Physiol. 2002 Feb;282(2):R411-22.
• Fan H, Zhang R, Tesfaye D, Tholen E, Looft C, Hölker M, Schellander K, Cinar MU. Sulforaphane causes a major epigenetic repression of myostatin in porcine satellite cells. Epigenetics. 2012 Oct 23;7(12).
• Totušek J, Tříska J, Lefnerová D, et al. Contents of Sulforaphane and Total Isothiocyanates, Antimutagenic Activity, and Inhibition of Clastogenicity in Pulp Juices from Cruciferous Plants. Czech J. Food Sci. 2011; 29(5): 548–556.
• Vermeulen M, Klöpping-Ketelaars IW, van den Berg R, Vaes WH. Bioavailability and kinetics of sulforaphane in humans after consumption of cooked versus raw broccoli. J Agric Food Chem. 2008 Nov 26;56(22):10505-9.

HIT Your Satellite Cells to Increase Your Gains! Only High Intensity "Cardio" Exercise Will Fuel Your Satellite Cell Pool and Set You Up For Future Muscle Growth.

Image 1: NO-mediated satellite cell
recruitement (Anderson. 2000)

You have read it on the SuppVersity, you have heard about it on Carl Lanore's Super Human Radio and the BodyRX Show and those of you who have seen videos or pictures from the latest New York City Marathon, should actually have been able to infer it from the way the "finishers" looked like. Intensity not duration is what counts, when doing "cardio". Yet, as a very recent (7 days old) study shows (Naito. 2011), High Intensity Training (HIT) will not only burn off your lovehandles, while keeping your muscles intact, it will also prime your musclefibers for future growth by increasing the number of satellite cells, the small dormant mononuclear progenitor cells that are sandwiched between the basement membrane and sarcolemma of the fibers of your muscle and are recruited, whenever your body feels that you could use a little more or have to replace some damaged muscle mass.

While I will go into more detail on how your muscles actually grow in the upcoming parts of the Intermittent Fasting Series, in the course of which I am going to explain how you should train, eat and sleep in order to exploit all three major pathways of skeletal muscle growth, I want to give you a sneak peak at what you are going to learn, by highlighting that protein synthesis, i.e. the accrual of muscle protein in existing myonuclear domains, and the recruitment of satellite cells to replace damaged or add new myonuclei are distinct processes. It should nevertheless be obvious that with all the protein synthesis of the world you will - sooner or later - hit a plateau, when all the existing myonuclei have "blown up" to their maximal size - or as Naito et al. put it: "Increases in the number of satellite cells are necessary for full skeletal muscle growth and hypertrophy" So, whenever the existing myonuclei have reached their "full potential", the only way to keep growing is by adding new myonuclei via satellite cell recruitment. Keep that in mind before you discard the results the following study, because the "HIT rats" did not gain more "active" muscle than the "LIT rats" ;-)

In their experiment Hasashi Naito and his colleagues from the Tokai University and the Juntendo University in Japan put 17-week old (these are old rats!) female Sprague-Dawley rats on one out of four exercise regimen (for a detailed outline of the regimen, cf. table 1):

1. High Intensity, High Duration (90H)
2. High Intensity, Low Duration (30H)
3. Low Intensity, High Duration (90L)
4. Low Intensity, Low Duration (30L)

Table 1: Outline of the exercise
protocol (from Naito. 2011)

In the course of the 10-week study period the rats were exercised five times a week on one of those funky rodent treadmills. What's funny is that despite the fact that, as the scientists say, "[e]lectrical shocks were used sparingly to motivate the animals to run", two of the critters in the high intensity groups refused to do their workouts, which reminds me of what Dr. Layne Norton had to say on one of the past installments of BodyRX Radio: "Most of those who will tell you that they cannot do HIT for whatever reasons are usually just too lazy" - we may thus consider those two lazy rats as evidence for the accuracy of the model... and by the way, it did not save them from being anesthetized and deprived of their plantaris muscle, which was weighed and analyzed for its fiber composition and satellite cell count.

As it was to be expected in view of the high age of the rats, where skeletal muscle mass maintenance, may be considered a success, there were no statistically significant increases in plantaris and/or body mass in any of the treatment groups.

Figure 1: Changes (compared to untrained control) in number of myonuclei and satellite cells per muscle fiber (data calculate base on Naito. 2011)

Despite the absence of measurable skeletal muscle hypertrophy, the pronounced (cf. figure 1) and fiber-type specific (cf. figure 2) increases in satellite cell counts in the high intensity groups may well be considered as the necessary prestage of a hypertophic growth spurt, which could be triggered by appropriate training (which would obviously be strength training) and endocrine (more on that in the conclusion) stimuli.

Figure 1: Satellite cells per muscle fiber in type I (slow twitch) and type II (fast twitch) muscle fibers of rats in the control and the high intensity, high duration (90H) groups (data calculate base on Naito. 2011)

In that, it is also interesting to note that contrary to popular believe, the slow-twitch type I fibers, with their greater number of satellite cells, have an increased propensity for maximal myonuclear numbers, the fable of the "hypertrophy-prone fast-twitch type II" fibers, on the other end, is a consequence of their ability to accumulate more protein per myonucleus. And while I will - as promised in the red box above - dig deeper into that in future installments of Sunday's Intermittent Thoughts, I can already tell you that the fiber composition (not the size!) of professional body builders is almost identical to those of non-strength-trained individuals and thusly fundamentally different from that of strength athletes, like powerlifters (Tesch. 1982) - in order to achieve maximal muscularity you can thusly not neglect your type I fibers!

That being said, both the strength training, which would make use of the increased propensity to grow by recruiting satellite cells to form new myonuclei, as well as the necessary local IGF and MGF responses, which have been shown to decrease with age (Grounds. 2002), were absent in the study at hand. In someone like you, a young, vigorous strength trainee, both stimuli will yet obviously be present in abundance (at least I would hope so ;-). Accordingly, 1-3 high intensity (and in view of the fact that the duration, 30 vs. 90min, did not make a difference probably also high intensity interval) training (HIT or HIIT) sessions per week could not only make your increasingly fat-free muscles shine in their full glory, they will also "precondition" you for future muscle growth by increasing your satellite cell pool. I would thus suggest, you better not join the two lazy rats from the study, and rather find yourself the next best track to do a bunch of sprints ;-)