# Muscle Hypertrophy



## GFR (Mar 30, 2006)

*The Mystery of Skeletal Muscle Hypertrophy
*Richard Joshua Hernandez, B.S. and Len Kravitz, Ph.D. 
* 								Introduction*
Through exercise, the muscular work done against a progressively challenging overload leads to increases in muscle mass and cross-sectional area, referred to as hypertrophy. But why does a muscle cell grow and how does it grow? Although an intense topic of research, scientists still do not fully understand the complete (and very complex) picture of how muscle adapts to gradually overloading stimuli. In this article, a brief but relevant review of the literature is presented to better understand the multifaceted phenomenon of skeletal muscle hypertrophy.

What is Muscular Hypertrophy?
Muscular hypertrophy is an increase in muscle mass and cross-sectional area (1). The increase in dimension is due to an increase in the size (not length) of individual muscle fibers. Both cardiac (heart) and skeletal muscle adapt to regular, increasing work loads that exceed the preexisting capacity of the muscle fiber. With cardiac muscle, the heart becomes more effective at squeezing blood out of its chambers, whereas skeletal muscle becomes more efficient at transmitting forces through tendonous attachments to bones (1).
 Skeletal muscle has two basic functions: to contract to cause body movement and to provide stability for body posture. Each skeletal muscle must be able to contract with different levels of tension to perform these functions. Progressive overload is a means of applying varying and intermittent levels of stress to skeletal muscle, making it adapt by generating comparable amounts of tension. The muscle is able to adapt by increasing the size and amount of contractile proteins, which comprise the myofibrils within each muscle fiber, leading to an increase in the size of the individual muscle fibers and their consequent force production (1).

* 								The Physiology of Skeletal Muscle Hypertrophy*
The physiology of skeletal muscle hypertrophy will explore the role and interaction of satellite cells, immune system reactions, and growth factor proteins (See Figure 1. for Summary).
*Satellite Cells*
Satellite cells function to facilitate growth, maintenance and repair of damaged skeletal (not cardiac) muscle tissue (2). These cells are termed satellite cells because they are located on the outer surface of the muscle fiber, in between the sarcolemma and basal lamina (uppermost layer of the basement membrane) of the muscle fiber. Satellite cells have one nucleus, with constitutes most of the cell volume.
 Usually these cells are dormant, but they become activated when the muscle fiber receives any form of trauma, damage or injury, such as from resistance training overload. The satellite cells then proliferate or multiply, and the daughter cells are drawn to the damaged muscle site. They then fuse to the existing muscle fiber, donating their nuclei to the fiber, which helps to regenerate the muscle fiber. It is important to emphasize the point that this process is not creating more skeletal muscle fibers (in humans), but increasing the size and number of contractile proteins (actin and myosin) within the muscle fiber (see Table 1. for a summary of changes that occur to muscle fibers as they hypertrophy). This satellite cell activation and proliferation period lasts up to 48 hours after the trauma or shock from the resistance training session stimulus (2). 

The amount of satellite cells present within in a muscle depends on the type of muscle. Type I or slow-twitch oxidative fibers, tend to have a five to six times greater satellite cell content than Type II (fast-twitch fibers), due to an increased blood and capillary supply (2). This may be due to the fact that Type 1 muscle fibers are used with greatest frequency, and thus, more satellite cells may be required for ongoing minor injuries to muscle.

*Immunology*
As described earlier, resistance exercise causes trauma to skeletal muscle. The immune system responds with a complex sequence of immune reactions leading to inflammation (3). The purpose of the inflammation response is to contain the damage, repair the damage, and clean up the injured area of waste products. 
 The immune system causes a sequence of events in response to the injury of the skeletal muscle. Macrophages, which are involved in phagocytosis (a process by which certain cells engulf and destroy microorganisms and cellular debris) of the damaged cells, move to the injury site and secrete cytokines, growth factors and other substances. Cytokines are proteins which serve as the directors of the immune system. They are responsible for cell-to-cell communication. Cytokines stimulate the arrival of lymphocytes, neutrophils, monocytes, and other healer cells to the injury site to repair the injured tissue (4).

The three important cytokines relevant to exercise are Interleukin-1 (IL-1), Interleukin-6 (IL-6), and tumor necrosis factor (TNF). These cytokines produce most of the inflammatory response, which is the reason they are called the ???inflammatory or proinflammatory cytokines??? (5). They are responsible for protein breakdown, removal of damaged muscle cells, and an increased production of prostaglandins (hormone-like substances that help to control the inflammation).
*Growth Factors*
Growth factors are highly specific proteins, which include hormones and cytokines, that are very involved in muscle hypertrophy (6). Growth factors stimulate the division and differentiation (acquisition of one or more characteristics different from the original cell) of a particular type of cell. In regard with skeletal muscle hypertrophy, growth factors of particular interest include insulin-like growth factor (IGF), fibroblast growth factor (FGF), and hepatocyte growth factor (HGF). These growth factors work in conjunction with each other to cause skeletal muscle hypertrophy.

*Insulin-Like Growth Factor*
IGF is a hormone that is secreted by skeletal muscle. It regulates insulin metabolism and stimulates protein synthesis. There are two forms, IGF-I, which causes proliferation and differentiation of satellite cells, and IGF-II, which is responsible for proliferation of satellite cells. In response to progressive overload resistance exercise, IGF-I levels are substantially elevated, resulting in skeletal muscle hypertrophy (7).

*Fibroblast Growth Factor*
FGF is stored in skeletal muscle. FGF has nine forms, five of which cause proliferation and differentiation of satellite cells, leading to skeletal muscle hypertrophy. The amount of FGF released by the skeletal muscle is proportional to the degree of muscle trauma or injury (8).

*Hepatocyte Growth Factor*
HGF is a cytokine with various different cellular functions. Specific to skeletal muscle hypertrophy, HGF activates satellite cells and may be responsible for causing satellite cells to migrate to the injured area (2). 
								Hormones in Skeletal Muscle Hypertrophy
Hormones are chemicals which organs secrete to initiate or regulate the activity of an organ or group of cells in another part of the body. It should be noted that hormone function is decidedly affected by nutritional status, foodstuff intake and lifestyle factors such as stress, sleep, and general health. The following hormones are of special interest in skeletal muscle hypertrophy.

*Growth Hormone*
Growth hormone (GH) is a peptide hormone that stimulates IGF in skeletal muscle, promoting satellite cell activation, proliferation and differentiation (9). However, the observed hypertrophic effects from the additional administration of GH, investigated in GH-treated groups doing resistance exercise, may be less credited with contractile protein increase and more attributable to fluid retention and accumulation of connective tissue (9).

*Cortisol*
Cortisol is a steroid hormone (hormones which have a steroid nucleus that can pass through a cell membrane without a receptor) which is produced in the adrenal cortex of the kidney. It is a stress hormone, which stimulates gluconeogenesis, which is the formation of glucose from sources other than glucose, such as amino acids and free fatty acids. Cortisol also inhibits the use of glucose by most body cells. This can initiate protein catabolism (break down), thus freeing amino acids to be used to make different proteins, which may be necessary and critical in times of stress.
 In terms of hypertrophy, an increase in cortisol is related to an increased rate of protein catabolism. Therefore, cortisol breaks down muscle proteins, inhibiting skeletal muscle hypertrophy (10). 

*Testosterone*
Testosterone is an androgen, or a male sex hormone. The primary physiological role of androgens are to promote the growth and development of male organs and characteristics. Testosterone affects the nervous system, skeletal muscle, bone marrow, skin, hair and the sex organs. 
 With skeletal muscle, testosterone, which is produced in significantly greater amounts in males, has an anabolic (muscle building) effect. This contributes to the gender differences observed in body weight and composition between men and women. Testosterone increases protein synthesis, which induces hypertrophy (11).

*Fiber Types and Skeletal Muscle Hypertrophy*
The force generated by a muscle is dependent on its size and the muscle fiber type composition. Skeletal muscle fibers are classified into two major categories; slow-twitch (Type 1) and fast-twitch fibers (Type II). The difference between the two fibers can be distinguished by metabolism, contractile velocity, neuromuscular differences, glycogen stores, capillary density of the muscle, and the actual response to hypertrophy (12).

*Type I Fibers*
Type I fibers, also known as slow twitch oxidative muscle fibers, are primaritly responsible for maintenance of body posture and skeletal support. The soleus is an example of a predominantly slow-twitch muscle fiber. An increase in capillary density is related to Type I fibers because they are more involved in endurance activities. These fibers are able to generate tension for longer periods of time. Type I fibers require less excitation to cause a contraction, but also generate less force. They utilize fats and carbohydrates better because of the increased reliance on oxidative metabolism (the body???s complex energy system that transforms energy from the breakdown of fuels with the assistance of oxygen) (12). 
 Type I fibers have been shown to hypertrophy considerably due to progressive overload (13,15). It is interesting to note that there is an increase in Type I fiber area not only with resistance exercise, but also to some degree with aerobic exercise (14).

*Type II Fibers*
Type II fibers can be found in muscles which require greater amounts of force production for shorter periods of time, such as the gastrocnemius and vastus lateralis. Type II fibers can be further classified as Type IIa and Type IIb muscle fibers. 

*Type IIa Fibers*
Type IIa fibers, also known as fast twitch oxidative glycolytic fibers (FOG), are hybrids between Type I and IIb fibers. Type IIa fibers carry characteristics of both Type I and IIb fibers. They rely on both anaerobic (reactions which produce energy that do not require oxygen), and oxidative metabolism to support contraction (12).
 With resistance training as well as endurance training, Type IIb fibers convert into Type IIa fibers, causing an increase in the percentage of Type IIa fibers within a muscle (13). Type IIa fibers also have an increase in cross sectional area resulting in hypertrophy with resistance exercise (13). With disuse and atrophy, the Type IIa fibers convert back to Type IIb fibers. 

* 								Type IIb Fibers*
Type IIb fibers are fast-twitch glycolytic fibers (FG). These fibers rely solely on anaerobic metabolism for energy for contraction, which is the reason they have high amounts of glycolytic enzymes. These fibers generate the greatest amount of force due to an increase in the size of the nerve body, axon and muscle fiber, a higher conduction velocity of alpha motor nerves, and a higher amount of excitement necessary to start an action potential (12). Although this fiber type is able to generate the greatest amount of force, it is also maintains tension for a shortesst period of time (of all the muscle fiber types). 
 Type IIb fibers convert into Type IIa fibers with resistance exercise. It is believed that resistance training causes an increase in the oxidative capacity of the strength-trained muscle. Because Type IIa fibers have a greater oxidative capacity than Type IIb fibers, the change is a positive adaptation to the demands of exercise (13).

*Conclusion*
Muscular hypertrophy is a multidimensional process, with numerous factors involved. It involves a complex interaction of satellite cells, the immune system, growth factors, and hormones with the individual muscle fibers of each muscle. Although our goals as fitness professionals and personal trainers motivates us to learn new and more effective ways of training the human body, the basic understanding of how a muscle fiber adapts to an acute and chronic training stimulus is an important educational foundation of our profession. 


*Table 1. Structural Changes that Occur as a Result of Muscle Fiber Hypertrophy*
Increase in actin filaments
								Increase in myosin filaments
								Increase in myofibrils
								Increase in sarcoplasm
								Increase in muscle fiber connective tissue
*Source: Wilmore, J.H. and D. L. Costill.  Physiology of Sport and Exercise (2nd Edition).Champaign, IL: Human Kinetics, 1999.*


References

1. Russell, B., D. Motlagh,, and W. W. Ashley. Form follows functions: how muscle shape is regulated by work. Journal of Applied Physiology 88: 1127-1132, 2000.

2. Hawke, T.J., and D. J. Garry. Myogenic satellite cells: physiology to molecular biology. Journal of Applied Physiology. 91: 534-551, 2001.

3. Shephard, R. J. and P.N. Shek. Immune responses to inflammation and trauma: a physical training model. Canadian Journal of Physiology and Pharmacology 76: 469-472, 1998.

								4. Pedersen, B. K.  Exercise Immunology. New York: Chapman and Hall; Austin: R. G. Landes, 1997. 

5. Pedersen, B. K. and L Hoffman-Goetz. Exercise and the immune system: Regulation, Integration, and Adaptation. Physiology Review 80: 1055-1081, 2000.

6. Adams, G.R., and F. Haddad. The relationships among IGF-1, DNA content, and protein accumulation during skeletal muscle hypertrophy. Journal of Applied Physiology 81(6): 2509-2516, 1996.

7. Fiatarone Singh, M. A., W. Ding, T. J. Manfredi, et al. Insulin-like growth factor I in skeletal muscle after weight-lifting exercise in frail elders. American Journal of Physiology 277 (Endocrinology Metabolism 40): E135-E143, 1999.

8. Yamada, S., N. Buffinger, J. Dimario, et al. Fibroblast Growth Factor is stored in fiber extracellular matrix and plays a role in regulating muscle hypertrophy. Medicine and Science in Sports and Exercise 21(5): S173-180, 1989.

9. Frisch, H. Growth hormone and body composition in athletes. Journal of Endocrinology Investigation 22: 106-109, 1999.

10. Izquierdo, M., K Hakkinen, A. Anton, et al. Maximal strength and power, endurance performance, and serum hormones in middle-aged and elderly men. Medicine and Science in Sports Exercise 33 (9): 1577-1587, 2001.

11. Vermeulen, A., S. Goemaere, and J. M. Kaufman. Testosterone, body composition and aging. Journal of Endocrinology Investigation 22: 110-116, 1999.

12. Robergs, R. A. and S. O. Roberts. Exercise Physiology: Exercise, Performance, and Clinical Applications. Boston: WCB McGraw-Hill, 1997.

13. Kraemer, W. J., S. J. Fleck, and W. J. Evans. Strength and power training: physiological mechanisms of adaptation. Exercise and Sports Science Reviews 24: 363-397, 1996.

14. Carter, S. L., C. D. Rennie, S. J. Hamilton, et al. Changes in skeletal muscle in males and females following endurance training. Canadian Journal of Physiology and Pharmacology 79: 386-392, 2001.

15. Hakkinen, K., W. J. Kraemer, R. U. Newton, et al. Changes in electromyographic activity, muscle fibre and force production characteristics during heavy resistance/power strength training in middle-aged and older men and women. Acta Physiological Scandanavia 171: 51-62, 2001.

16. Schultz, E. Satelite cell behavior during skeletal muscle growth and regeneration. Medicine and Science in Sports and Exercise 21(5): S181-S186, 1989


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## G20 (Mar 30, 2006)

Intresting read


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## Dale Mabry (Mar 30, 2006)

ForemanRules said:
			
		

> necrosis factor




RACIST!!!!!!!!!!!!!!!!!!

Good read, interesting how type IIB convert to type IIA as an adaptation to resistance training.  I've read that somewhere before.


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## Tough Old Man (Mar 30, 2006)

Where is type IIC fiber that Iron Man is always talking about. I see Type II (A), (B) but no (C)


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## Dale Mabry (Mar 30, 2006)

If you wanted to, you could break them down into 7 types, but it is unnecessary for our purposes.  If you need to know, C are only used for IC, IIC, and IIAC and are moderate to low in contraction velocity.  Certainly not necessary to go to that level of detail, you couldn't base a porgram off of it.  As far as I know, only scientists use it.


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## P-funk (Mar 30, 2006)

good read.  Len Kravitz is a smart guy.  By chance, do you have the link this came from so that we (or I) can see the Figures that he is reffering to in the text?  Or can you scan them in if this is from a text book?




> Good read, interesting how type IIB convert to type IIA as an adaptation to resistance training. I've read that somewhere before.



It is strange because I have always read that they don't change literally into type IIa fibers...they just alter their characteristics.  The best way to stimulate those type IIB fibers is to do higher velocity or high power exercises (the dynamic effort method).


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## BigDyl (Mar 30, 2006)

Dale Mabry said:
			
		

> If you wanted to, you could break them down into 7 types, but it is unnecessary for our purposes.  If you need to know, C are only used for IC, IIC, and IIAC and are moderate to low in contraction velocity.  Certainly not necessary to go to that level of detail, you couldn't base a porgram off of it.  As far as I know, only scientists use it.


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## Dale Mabry (Mar 30, 2006)

P-funk said:
			
		

> It is strange because I have always read that they don't change literally into type IIa fibers...they just alter their characteristics.  The best way to stimulate those type IIB fibers is to do higher velocity or high power exercises (the dynamic effort method).




"They take on the characteristics of" is probably more appropriate, but under a microscope I believe the 2 look completely different and that is why it is said they are converted to.  The more and more I read about it, the more and more likely it seems that you can't really train these fibers.  Maybe it is different in some people, but from what I gather, their endurance capacity is so low that any training causes the shift towards IIa characteristics.


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## Dale Mabry (Mar 30, 2006)

BigDyl said:
			
		

>



You contribute so much, I don't know if words could ever express it.


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## Mike Tuvre USA (Mar 30, 2006)

Can someone give an example of how Type I's are stimulated vs type II's during a set of bench presses?  Do Type I's provide the same growth as Type II's?  I did see that utilizing Type I's is best for burning fats and carbs.  Good for cutting, no?  Would you recommend working all the fibers in the same workout?  That was a good article.  Thanks.


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## P-funk (Mar 30, 2006)

Mike Tuvre said:
			
		

> Can someone give an example of how Type I's are stimulated vs type II's during a set of bench presses?  Do Type I's provide the same growth as Type II's?  I did see that utilizing Type I's is best for burning fats and carbs.  Good for cutting, no?  Would you recommend working all the fibers in the same workout?  That was a good article.  Thanks.




type I's are endurance type fibers.  they are slow to farigue.  if you were doing very high repetitions on the bench press you would stress a greater amount of these types of fibers.

type II fibers and more specifically type IIa fibers are going to be stressed during anerobic activities.  they have a greater potential for hyerprophy and they are faster to fatigue then type I fibers yet slower to fatigue then type IIb fibers.  This is why they are called fast-oxadative fibers.  The best rep range that you can use to stimulate these would be around 6-12 repetitions.  this is what we generically refer to as "the hypertrophy rep range".

working on all fiber types is important.  this can be done by making sure that you periodize your workout so that you work through a variety of different rep ranges in your training program at different times.

continuing to lift heavy is important when dieting/cutting.  it helps to maintain muscle mass.  use it or loose it.


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## P-funk (Mar 30, 2006)

Dale Mabry said:
			
		

> "They take on the characteristics of" is probably more appropriate, but under a microscope I believe the 2 look completely different and that is why it is said they are converted to.  The more and more I read about it, the more and more likely it seems that you can't really train these fibers.  Maybe it is different in some people, but from what I gather, their endurance capacity is so low that any training causes the shift towards IIa characteristics.




I don't know.  Doesn't Sandler talk about stimulating type IIb fibers in his Sports Power book?

I believe Zatsiorsky talks about it in Science and Principles of Strength training when he gets into the dynamic effort and fiber recruitment.


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## Dale Mabry (Mar 30, 2006)

P-funk said:
			
		

> I don't know.  Doesn't Sandler talk about stimulating type IIb fibers in his Sports Power book?
> 
> I believe Zatsiorsky talks about it in Science and Principles of Strength training when he gets into the dynamic effort and fiber recruitment.




From what I understand, they are the highest threshold units and there is a positive correlation between people who start with a higher percentage of these and people who excel in power sports.  But, since they are the highest threshold motor units and are easily fatigued, they adapt by taking on the characteristics of IIa fibers when they are hit more often.  Thus, training leads to a change to IIa characteristics.  So, the more you train at a certain weight near your max, the more they take on IIa characteristics to adapt, thus new IIB fibers need to be recruited and the cycle continues.

So let's say your max right now is 350lbs in a lift.  As you train, you eventually get 350 a few times.  By that time, those IIB fibers have taken on IIA charactersitics, and you are working on recruiting the next highest threshold IIB fibers to get 365 for a max.


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## CowPimp (Mar 30, 2006)

Dale Mabry said:
			
		

> From what I understand, they are the highest threshold units and there is a positive correlation between people who start with a higher percentage of these and people who excel in power sports.  But, since they are the highest threshold motor units and are easily fatigued, they adapt by taking on the characteristics of IIa fibers when they are hit more often.  Thus, training leads to a change to IIa characteristics.  So, the more you train at a certain weight near your max, the more they take on IIa characteristics to adapt, thus new IIB fibers need to be recruited and the cycle continues.
> 
> So let's say your max right now is 350lbs in a lift.  As you train, you eventually get 350 a few times.  By that time, those IIB fibers have taken on IIA charactersitics, and you are working on recruiting the next highest threshold IIB fibers to get 365 for a max.



That's a wild possibility.  So, are you suggesting that the most elite athletes have almost no pure IIB fibers, and most of them have been converted to IIA fibers?


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## Dale Mabry (Mar 31, 2006)

CowPimp said:
			
		

> That's a wild possibility.  So, are you suggesting that the most elite athletes have almost no pure IIB fibers, and most of them have been converted to IIA fibers?




See, I don't know about that.  Sandler is a pretty smart guy and is unclear about that in his book.  I don't think anybody knows for sure, but that could be a possibility, or another possibility is that elite athletes are freaks and their IIB just don't convert for some reason.  Or maybe since they start out with a very high concentration, they end up with a higher concentration than most.

Probably be impossible to know since most athletes start training when they are super young and I don't imagine anyone is in a hurry to give a 10yr old a muscle biopsy.


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## BigDyl (Mar 31, 2006)

Dale Mabry said:
			
		

> You contribute so much, I don't know if words could ever express it.




True Story, I've got "something" to contribute right now...


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## CowPimp (Mar 31, 2006)

Dale Mabry said:
			
		

> See, I don't know about that.  Sandler is a pretty smart guy and is unclear about that in his book.  I don't think anybody knows for sure, but that could be a possibility, or another possibility is that elite athletes are freaks and their IIB just don't convert for some reason.  Or maybe since they start out with a very high concentration, they end up with a higher concentration than most.
> 
> Probably be impossible to know since most athletes start training when they are super young and I don't imagine anyone is in a hurry to give a 10yr old a muscle biopsy.



What's the book?


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## Dale Mabry (Mar 31, 2006)

Sport Power, it only has a blurb on it, basically saying they don't know if fiber conversion occurs.  But it is a great book.  And short and to the point.


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## CowPimp (Mar 31, 2006)

Dale Mabry said:
			
		

> Sport Power, it only has a blurb on it, basically saying they don't know if fiber conversion occurs.  But it is a great book.  And short and to the point.



Cool.  I'll add that to the list.  

I need to get through this damned cert exam so I can start reading some other physiology texts.  Not that I haven't learned anything from the textbook, but I think there is a lot more cutting edge information out there that I need to get ahold of.  I just can't pull myself to read two physiology texts at the same time; I like to read from other genres as well, heh.


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## Dale Mabry (Mar 31, 2006)

Which test are you taking, the NSCA-CPT?  I only read the NSCA Essentials book the entire year before taking the test, so many books have differing information.  Needless to say it was boring as hell for that year but it paid off.


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## P-funk (Mar 31, 2006)

Here is Some Stuff from Supertraining by Mel Siff.

I will paraphrase from pages 55-58



> Type IIx (IIB or FTb) fibres are fast contracting, whitish, low myoglobin fibres with a large diameter, high glycolitic capacity, low oxidative capacity and few mitochondria.  They are suited to high power output and are usually recruited only where very rapid or very intense effort is required, as in field athletics and weightlifting, where athletes in these sports exhibit high percentages of these fibres (Abernethy, 1994; Tesch, 1998).  They fatigue rapidy and replenish their energy supplies mainly after exercise has ceased.  Interestingly, some studies reveal that bodybuilders often display a smaller percentage of type IIX/B Myosin Heavy Chain (MHC)  isoforms than untrained controls or even endurance-trained subjects (Jurimae et al, 1997)......
> 
> Fiber types differe considerably between individuals, especially between endurance and strength athletes.  For instance, vastus medialis biopsies reveal that the proportion of FT fibres in field athletes and weightlifters can be over three times (ie over 60% FT fibres) greater then that of marathon runners (aprox. 17% FT fibres) and 50% greater than that of bodybuilders., cyclists and race walkers (all about 40% FT fibres).  The importance of fast fibres in short duration explosive or maximal strength efforts is underscored by the fact that fast type IIx fibres contract 10 times faster than slow type I fibres (Anderson et al, 2000).
> 
> ...



Okay, now that is fine.  Here is the good stuff and why I think you can target your typeIIx (IIB) fibres in training:

from pg. 58; Supertraining



> Although research indicates that fibre distribution is strongly determined by genetic factors, it appears as if these differeneces may also be strongly influenced by the type, intensity and duration of trauining, as well as the pre-training status of the individual.  This becomes particularly evident if the muscle fibre distribution is compared between weightlifters and bodybuilders.  Weightlifters have a considerably higher proportion of FT fibres, a fact which cannot be explained by the contention that specific genetic types excel at specific sports.  Bodybuilders have about 10% fewer FT fibres (or 10% more ST fibres) than untrained subjects, while weightlifters have about 10% more FT fibres.  It is apparent that even the specifi types of strength training may influence the relative proportions of FT and ST fibres and their hybrid sub-types.  The difference between weightlifters and bodybuilders probably lies in the fact that weightlifters usually execute considerably more low repetition, maximal effort, explosive training than bodybuilders, who often use moderate loads slowly to failure.




I think it has to do with the specificity of training.  I mean, even if you look at powerlifters of today.  Even though they train the dynamic effort method, they still do high volumes of assistance work in the repetition method.  While olympic weightlifters don't do any of this (most of the time).  Usually it is fast, explosive movements when performing their competitive lifts (dynamic effort), quick pulls with heavy weight at loads >100% of their maximum efforts in their competitive lifts (maximal effort) and then squats at <3 repetitions (maximal effort).  Rarely do they ever perform the repetitive effort.

What do you guys think?


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## Dale Mabry (Mar 31, 2006)

It can be explained for in genetics.  I mean, the people who excel at weightlifting may just not get any conversion at all.  Could be related to training too, though.  Could also have to do with neuro-factors as well.  

I don't know how he can eliminate the likelihood that people who are built for something are automatically drawn to it.  There is such strong evidence.  If you look in the Strength and conditioning journals, all of the data that is collected is from professionals of whatever sport they are looking at.  I think with sprinters you are pretty much born with olympic speed or not, I don't think you can take a kid and train him if he doesn't have the genetics.  You won't be sprinting olympic speed out of the vagina, but you have a certain distribution of fibers that is optimal.  Now, there are probably people with an optimal percentage of a type of fiber that just choose not to train or compete, and those people will never have data beause how would you know who to test?  I imagine most of the people studied compete, I know I would never compete if I wasn't good at something.  


I am not that informed with powerlifting, but another theory could be that they started in adolescence with powerlifting and it shaped the way they went thru puberty.

I think the main take home message from it all is that nobody really knows anything and no one is really looking into funding this sort of stuff so that won't change anytime soon.

BTW, my stance isn't that you can't hit IIb fibers, it's that the only adaptation that they make will be to convert to IIa fibers.  I think that neurofactors have more to do with it than anything, holding percentage of fibers constant.


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## P-funk (Mar 31, 2006)

Dale Mabry said:
			
		

> I think the main take home message from it all is that nobody really knows anything and no one is really looking into funding this sort of stuff so that won't change anytime soon.




I agree.  i am just throwing it out there.



> BTW, my stance isn't that you can't hit IIb fibers, it's that the only adaptation that they make will be to convert to IIa fibers.  I think that neurofactors have more to do with it than anything, holding percentage of fibers constant.



yea, I agree with this too.  I thought you were saying that you can't target them in training.  yea, their biggest adaptation is going to be conversin to type IIa fibers due to resistance training.


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## Dale Mabry (Mar 31, 2006)

P-funk said:
			
		

> I agree.  i am just throwing it out there.
> 
> 
> 
> yea, I agree with this too.  I thought you were saying that you can't target them in training.  yea, their biggest adaptation is going to be conversin to type IIa fibers due to resistance training.




I think that while it is meant to be a positive adaptation, for those looking for power it is probably not good.  I wonder how it factors into the non-sequential recruitment stuff you posted before (Where high threshold units are recruited before low threshold units in some power athletes).  

I wish there was a budget to do this kind of stuff, it sucks.  I would never want to do it myself, but the info would be valuable.


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## P-funk (Mar 31, 2006)

Dale Mabry said:
			
		

> I think that while it is meant to be a positive adaptation, for those looking for power it is probably not good.  I wonder how it factors into the non-sequential recruitment stuff you posted before (Where high threshold units are recruited before low threshold units in some power athletes).
> 
> I wish there was a budget to do this kind of stuff, it sucks.  I would never want to do it myself, but the info would be valuable.




it is simple really.  we just start stealling money.  we will rob banks from here to AZ.


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## CowPimp (Mar 31, 2006)

Dale Mabry said:
			
		

> Which test are you taking, the NSCA-CPT?  I only read the NSCA Essentials book the entire year before taking the test, so many books have differing information.  Needless to say it was boring as hell for that year but it paid off.



Yeah, the CPT.  I don't have a 4 year degree.  I'm not eligible to take the CSCS, but I will get that at some point too.


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## CowPimp (Mar 31, 2006)

Dale Mabry said:
			
		

> BTW, my stance isn't that you can't hit IIb fibers, it's that the only adaptation that they make will be to convert to IIa fibers.  I think that neurofactors have more to do with it than anything, holding percentage of fibers constant.



If you take your previous statement into account...



> I think the main take home message from it all is that nobody really knows anything and no one is really looking into funding this sort of stuff so that won't change anytime soon.



That's somewhat assumptive.  Of course, you are certainly entitled to make educated guesses about these things.  That's the best we can do right now.  I somehow doubt that the body is incapable of shifting IIA fibers in the direction of IIB fibers.  The human body is too amazing of an adaptive machine for me to totally forgoe that possibility without seeing some more concrete evidence as such.  Or, maybe we have sufficient numbers already, and it is just damned near impossible to tap into the neural pathways necessary to utilize them 100%.  Who knows...


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## Dale Mabry (Mar 31, 2006)

CowPimp said:
			
		

> If you take your previous statement into account...
> 
> 
> 
> That's somewhat assumptive.  Of course, you are certainly entitled to make educated guesses about these things.  That's the best we can do right now.  I somehow doubt that the body is incapable of shifting IIA fibers in the direction of IIB fibers.  The human body is too amazing of an adaptive machine for me to totally forgoe that possibility without seeing some more concrete evidence as such.  Or, maybe we have sufficient numbers already, and it is just damned near impossible to tap into the neural pathways necessary to utilize them 100%.  Who knows...




I am not positive, but I think the way they are innervated prevents that from happening, ie., the threshold of the nerve that fires the IIa fibers is set so there would be no reason to change from IIa to IIb.  But IIb fibers, once they are used to enough, would have a need to convert to IIa fibers for endurance.  Again, I have no idea if that is right, but I think that is how Sandler describes it.


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