# Who knows about fast/slow twich fibers



## HyDr8 (Jun 23, 2003)

Can a person have both? Are certain muscle groups more likely to be slow vs fast? How do you know what you have? How do you train them?

I know, a lot of questions but I have never gotten a grip on this topic.

Thanks


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## Mudge (Jun 23, 2003)

Yes, everyone has a mixture of both. According to what I've read you can even change your percentages through training.

How do you know? I think you'd have to cut open the specific bodypart in question to take a peek. If they have density differences I dont know of it. If it were the case though an XRay might be enough to get a guess.

I dont see that its critical to know though. Either you run fast, or you have lots of endurance, or are somewhere in the middle.

You train them exactly how you want to train them, if you sprint you will favor fast twitch muscle growth - if you run marathons you will favor slow twitch endurance fibers.


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## gr81 (Jun 23, 2003)

fast twitch fibers are recruited with brief, more intense stress put on the muscle (such as sprinting and other types of plyometrics) as where slow twitch fibers are recruited during less intense higher rep sets. It is crucial to know this when training certain bodyparts such as the hamstrings and calves, which are both primarily made up of fast twitch fibers.


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## gopro (Jun 24, 2003)

Here is an article that I wrote for IM some time ago, but it should help you out:



When the average person takes a look at a bodybuilder all he sees is a series of lumps and bumps of varying shapes and sizes. Upon inspection he may find these odd protrusions to be fascinating, cool, or perhaps grotesquemaybe even a little intimidating. But little does he know how complex and intricate all these "lumps" really are!

Let's take a look inside these lumps, see what they are made of and what we can do to make them bigger and stronger. Ok, first let me stop calling them lumps or bumps and refer to them more properly as skeletal muscles, or just muscles for short.

  Muscle is composed of bundles of muscle fibers or myofibers. Each fiber is composed of myofibrils, which, in turn, are composed of myofilaments. The myofilaments are made up of two proteins called myosin and actin. The myosin and actin act within the smallest functional unit of muscle, the sarcomere, to produce a contraction. It is the myosin protein, however, which holds the key to the differences in muscle fiber types. (Complicated lumps these muscles, aren't they!) In general, there are four different fiber types in skeletal muscle. These four include: Type I, also known as slow-twitch or red fibers; Type IIA, IID, and IIB, also known collectively as fast-twitch or white fibers.

  Type I are the slowest, smallest, and have the highest level of endurance of all the fibers. Next come the Type IIA, IID, and finally the Type IIB, which are the fastest, largest, and least endurance oriented in the group.

  As you contract a muscle, you'll recruit those muscle fibers in a specific order. The smallest (lowest threshold) fibers, the Type I, are recruited first. As the speed or force of contraction is increased, you will sequentially recruit the Type IIA, IID, and IIB muscle fibers. However, to recruit the Type IIB fibers it may take over 90% of a maximal contraction!

  All people are born with these muscle fiber types. Most muscles contain almost an even split of slow (Type I) and fast (Type II) fibers. There are a few exceptions, however, as the soleus muscle of the calf is predominantly slow twitch, while the gastrocnemius muscle and the hamstrings are predominantly fast twitch. Also, individuals on opposite ends of the athletic spectrum like sprinters and marathon runners for example, may possess a higher percentage of one fiber type.

  So what does this mean to all of us bodybuilders? Well, in order to obtain maximal muscle size we must regularly train all of our muscle fibers. A combination of bodybuilding (higher and lower rep), powerlifting, and even a little Olympic-style lifting may be best. Bodybuilding seems to stress the Type I and IIA fibers, while the IIB fibers may be best stimulated through powerlifting and Olympic lifting. The IID fibers are perhaps stressed equally by all three forms of training. I believe that the key to long term progress in bodybuilding can be summed up by one important word: VARIATION!

  Doing the same three sets of 8-12 reps over and over will help you to a point. But after that, make a change! By selectively alternating your training volume (total sets/reps), training intensity (weight lifted), training techniques (forced reps, pre-exhaust, supersets, drop sets, etc.), training tempo (rep speed), rest between sets, bodypart arrangement, etc., you're more likely to avoid injuries and overtraining and therefore maximize your gains. As long as the stimulus presented to your muscles is novel and taxing, they will continue to adapt accordingly.

  Just remember that your muscle fibers are not static entities they are dynamic and malleable. Therefore you yourself should not be static-don't do the same thing over and over and expect a different result. Don't get stuck in just one type of training program! Be creative! Be dynamic! Your muscles will reward you with continuous gains in size, strength, and endurance. Now, go get to work on those "lumps!"


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## Robboe (Jun 24, 2003)

Ahh yes, the infamous "type IId" muscle fibre article.

I remember this like it was just yesterday...


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## HyDr8 (Jun 24, 2003)

Thanks for the repiles guys. Gopro, thanks for your post too. That clears up a few things for me.


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## Arnold (Jun 24, 2003)

> _*Originally posted by HyDr8 *_
> Can a person have both? Are certain muscle groups more likely to be slow vs fast? How do you know what you have? How do you train them?
> 
> I know, a lot of questions but I have never gotten a grip on this topic.
> ...



I also wrote an article recently that explains this briefly: 
Training and Hypertrophy - Gain Size!


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## gopro (Jun 24, 2003)

TCD unfortunately is without any muscle fiber and cannot relate to this question at all.


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## gopro (Jun 24, 2003)

> _*Originally posted by HyDr8 *_
> Thanks for the repiles guys. Gopro, thanks for your post too. That clears up a few things for me.



You are welcome.


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## gopro (Jun 24, 2003)

> _*Originally posted by The_Chicken_Daddy *_
> Ahh yes, the infamous "type IId" muscle fibre article.
> 
> I remember this like it was just yesterday...



Dude, please...you don't have the mental capacity to remember as far back as yesterday...


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## FortifiedIron (Jun 25, 2003)

> _*Originally posted by gopro *_
> Here is an article that I wrote for IM some time ago, but it should help you out:
> 
> 
> ...




Much respect for that piece. Except Im not familiar with the term IID fiber. If you could please clear it up.  

Just a tid bit of info, the IIB has been out dated for human's. The FT classification fiber is now the IIX for humans. IIB is only found in mammal life other then us humans. Was a huge study conducted on this information.

I also find it pretty good that you mention the benefits of Olifting and Pling to a bodybuilder. SOmething alot of bbers are overlooking these days.


Kc


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## Robboe (Jun 25, 2003)

Kyle, look up rat muscles. You'll definately find type IId there.


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## gopro (Jun 25, 2003)

> _*Originally posted by The_Chicken_Daddy *_
> Kyle, look up rat muscles. You'll definately find type IId there.



I see that I now stand corrected....TCD does have type II D fibers after all...


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## Robboe (Jun 25, 2003)

Very humerous, Eric.

Still doesn't correct you though.


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## gopro (Jun 25, 2003)

> _*Originally posted by The_Chicken_Daddy *_
> Very humerous, Eric.
> 
> Still doesn't correct you though.



I don't need correction Chicken...when I wrote the article some time ago the research came from Jose Antonio who believed, or believes there are type II D fibers in humans...and also, back then type II B fibers were also desrcibed in humans (to answer Fortified...or your buddy Kyle).

So, go bother him about it, k? I've got more important things to do.


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## Arnold (Jun 25, 2003)

you two should have your insult exchanges via PM's, it only degrades threads.


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## Robboe (Jun 25, 2003)

I fail to see where i have insulted him in this thread.

End of the day, the "science" behind his article, the outcome of which doesn't necessarily equate to the description beforehand, is wrong and now outdated. He's been told last year that it is wrong and yet he still posted it here. He should either re-write the article or not post it at all.

Eric referenced one study relating to the type IId fibre - the abstract of which i found online (and will happily find again if you so desire). The abstract stated that the study was done using rats quite clearly.

Either he bluffed that he'd read the study or needs quite a serious course in comprehending literature.


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## FortifiedIron (Jun 25, 2003)

Here is an abstract from my article:

4.) What is a muscle fiber?

Your body contains thousands and thousands of muscle fibers. Several of these fibers are bundled together to make up a fasciclei (plural, fasciculi) which is encased in a sheath called a perimysium. Many groups of these fasciculi form the whole muscle, which is then enclosed in another sheath called the epimysium (or fascia). Each fiber cell has several thousand rod-like structures known as myofibrils. Myofibrils consist of a chain of basic contractile units known as sacromeres. Sacromeres consist of both myosin and actin filaments. There are also small areas of the myosin filaments that are called cross bridges. These cross bridges are temporary connected to certain parts of the action filaments that form the basic components for a muscular contraction.

Myosin plays a special role in determining the contractility of the muscle. The myosin heavy chain (MHC) appears in three different iso-forms. They are referred to as I, IIa, and IIx forms. They are also located in the muscle fiber that contains them I-I, IIa-IIa, and IIx-IIx. Ia fibers are referred to as slow twitch muscle fibers (ST/Red), whereas IIa and IIx are referred to as fast twitch muscle fibers(FT/White). Type IIx is the fasting contractile muscle fiber. IIx has a contractile velocity 10 times that of a Ia fiber, where IIa lies between them. I, IIa and IIX fibers also have various other forms as well. These fibers are known as hybird fibers. They are scarce in young people but rather common in adults. 

The differences in fiber proportions in the muscles varies dramatically according to the person's genetics and training history. It has been revealed that the elite track athletes and Olympic styles weightlifters (over 60% FT fibers) have three times the fast twitch muscle fibers than that of marathon runners (17% FT) and 50% greater than in bodybuilders (40% FT fibers). Sub-maximal and high explosive weight training also produces greater hypertrophy of FT fibers. The potential for the body to generate high power output in Olympic style weightlifting movements and other forms of speed movements is greatly determined by the proportion of FT fibers. 

In every movement different muscle fiber types are recruited and fired. The velocity, load, and duration of the movement determines which fiber type is most dominantly recruited and fired. The first fiber is the Ia which is resistance to fatigue and lasts a prolonged period of time. The second fiber recruited is the IIa which is a fast twitch fiber which lasts an intermediate amount of time. The last fiber to be recruited is the IIX fiber which also has the strongest contractile output. Olympic lifters have a higher firing rate of FT fibers then ST fibers, whereas bodybuilders have a higher firing rate of ST fibers then FT fibers. The reason for the differences is Olympic lifters train with lower repetition sets, where their resistance is heavier and more explosive then that of a bodybuilder who normally trains with moderately heavy weight slowly to failure. 

(Andersen et al, 2000;Hakkinen, 1985) 
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I personally do not have a clue what IID is, I've spent alot of time studying in this area, its the first i've heard of it. Im not saying either is wrong or write. Its just strickingly odd to me. The only studies I have ever read that had to do with rats/lab animals was when i was studying hyperplasia. Yet I still didnt not find the term IID used. I'll look it up in my books later this afternoon.


Kc


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## FortifiedIron (Jun 25, 2003)

IID has to be a term used for hyperplasia fibers. Its a 100% proven 'theory'

What is hyperplasia?

Very little is known about hyperplasia. Hyperplasia is the splitting of muscle fibers. There has been testing done with animals such as cats (and rats) that have shown muscle fiber splitting. These cats where subjected to heavy resistance training for a prolonged period of time. It has also been noted that many Russian scientists have conclusively come to the finding that muscular mass is not only through hypertrophy of muscle fibers (enlarging) but also as an increase in fiber number by means of splitting into smaller sections. It has also been documented that satellite cells, which can activate new cell formation, have been shown to be associated with muscle hyperplasia, through stretching and dynamic exercises. Many people believe that hyperplasia does exist in humans possibly through heavy intensive training sessions, but lack of human testing cannot conclude this.

(Gudz, 1968,1976;Gonyea, 1980; Hether et al, 1991; Tamaki et al, 1992; *Antonio* & Gonyea, 1994)


other cites to Antonio's study on hyperplasia:

Antonio J & Gonyea W (1993) Skeletal muscles fiber hyperplasia Med SCI Sports Exerc Dec; 25(12): 1333-45

Still digging for more info so plz be patient.


Kc


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## Robboe (Jun 25, 2003)

Here's a link to the study Gopro originally cited as his reference: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1858863&dopt=Abstract


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## gopro (Jun 25, 2003)

I didn't reference any article. I wrote the article from notes that I had gathered from several sources, one of which was an article by Jose Antonio PHD.

Trust me, I do not need a lesson from either TCD of FI on fiber types, hyperplasia, or any other subject relating to this field. I am extremely well schooled in the subject and could write a book on it if I felt like it.

I posted the article just to give the original poster some basic info.


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## Twin Peak (Jun 25, 2003)

GoPro, I don't know shit about fiber types, but if there is no evidence that IId fiber types exist in humans, and indeed there is evidence to the contrary (I am not going to bother to look) than that is shameful.


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## FortifiedIron (Jun 25, 2003)

> _*Originally posted by gopro *_
> I didn't reference any article. I wrote the article from notes that I had gathered from several sources, one of which was an article by Jose Antonio PHD.
> 
> Trust me, I do not need a lesson from either TCD of FI on fiber types, hyperplasia, or any other subject relating to this field. I am extremely well schooled in the subject and could write a book on it if I felt like it.
> ...




Im not here to disprove or prove you wrong. I just have never heard of the IID fiber ever used. Now that I know what it is, I have furthur educated myself on the subject. 

Why you didnt cite the information from the article I have no clue. 

If you can write a book on the subject plz be my guest, id love to read it and give it my review. If you ever feel like you can and do plz contact me. 


Kc


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## Robboe (Jun 25, 2003)

> _*Originally posted by gopro *_
> I didn't reference any article. I wrote the article from notes that I had gathered from several sources, one of which was an article by Jose Antonio PHD.



The link i posted was the title you gave on WBB when you were first queried about your inclusion of type IId fibres in your article.

I will re-state: I think you may need "schooling" on how to comprehend what you read, if in fact you did read it at all.

If you could write a book then i implore you to. Of course i imagine it'll just be a cut & paste job, which the article you posted above very much resembles, save for the last three paragraphs.


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## Snake_Eyes (Jun 25, 2003)

> _*Originally posted by FortifiedIron *_
> Your body contains thousands and thousands of muscle fibers. Several of these fibers are bundled together to make up a fasciclei (plural, fasciculi) which is encased in a sheath called a perimysium. Many groups of these fasciculi form the whole muscle, which is then enclosed in another sheath called the epimysium (or fascia). Each fiber cell has several thousand rod-like structures known as myofibrils. Myofibrils consist of a chain of basic contractile units known as sacromeres. Sacromeres consist of both myosin and actin filaments. There are also small areas of the myosin filaments that are called cross bridges. These cross bridges are temporary connected to certain parts of the action filaments that form the basic components for a muscular contraction.
> 
> Myosin plays a special role in determining the contractility of the muscle. The myosin heavy chain (MHC) appears in three different iso-forms. They are referred to as I, IIa, and IIx forms. They are also located in the muscle fiber that contains them I-I, IIa-IIa, and IIx-IIx. Ia fibers are referred to as slow twitch muscle fibers (ST/Red), whereas IIa and IIx are referred to as fast twitch muscle fibers(FT/White). Type IIx is the fasting contractile muscle fiber. IIx has a contractile velocity 10 times that of a Ia fiber, where IIa lies between them. I, IIa and IIX fibers also have various other forms as well. These fibers are known as hybird fibers. They are scarce in young people but rather common in adults.
> ...



This is pretty much dead-on.

The only thing I have to add is that metabolic character, while related to MHC expression (and thereby shortening velocity, which is a function of the MHC isoform, and MU innervation), is wholly independent of any of the above qualities.

That is, whether a fiber is oxidative, glycolytic, or hybrid is related to the fiber's function, not its capability.

This is why training in regards to muscle fibers is practically useless. One should train either for neural function or metabolic character. Trying to organize training around "targeting" specific fibers is next to useless.

For example, one cannot train the vast majority of ST fibers without extreme endurance exercise, as most of them have fatigue times over several minutes up to several hours. No standard weight training will effect these to any meaningful degree.


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## Robboe (Jun 25, 2003)

Crikey.

I think this is the time where i casually slinker off, cause this is over my head now.


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## FortifiedIron (Jun 25, 2003)

> _*
> For example, one cannot train the vast majority of ST fibers without extreme endurance exercise, as most of them have fatigue times over several minutes up to several hours. No standard weight training will effect these to any meaningful degree. *_


_*


Are you trying to suggest that by slow, controlled movements done to exceed up to 10+ reps will not greatly effect the recruitment and fire of ST fibers?


Kc*_


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## Snake_Eyes (Jun 25, 2003)

Pretty much, yup.

The true oxidative type I fibers have exceedingly high fatigue thresholds.....I can't see a set short of 50-100 reps doing anything for the vast majority of them.


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## gopro (Jun 25, 2003)

> _*Originally posted by The_Chicken_Daddy *_
> The link i posted was the title you gave on WBB when you were first queried about your inclusion of type IId fibres in your article.
> 
> I will re-state: I think you may need "schooling" on how to comprehend what you read, if in fact you did read it at all.
> ...



A. I gave no references with my article...someone else may have found the link

B. I could and eventually will write a book, but it will involve all aspects of fitness/nutrition/drugs/supplements/contest prep/personal training/gym ownership/and more. You can go read the 3 articles that I wrote for MMI to see whether they were cut and paste, or go ask the CEO of VPX why he headhunted me out of thousands upon thousands of people in the industry to head up his websites, write for the magazine, write ad copy, and represent the company at seminars and other functions.

C. I crack up at the thought that "I" need more schooling to learn to comprehend what I read, as I'm sure that I have more knowledge in my small toe than you have in your entire head.

I also find it sooo hilarious that you need to bring "backup" with you everytime you want to get another wasteful point across.

Please Chicken, I IMPLORE YOU...dude, get a life.


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## Robboe (Jun 26, 2003)

> _*Originally posted by gopro *_
> A. I gave no references with my article...someone else may have found the link



Again, your comprehension skills are marvellous. I didn't say you gave a reference with your article. In fact, your article had no references. I said "The link i posted was the title you gave on WBB when you were first queried about your inclusion of type IId fibres in your article." 

In laymans - when you were called out, this is the study you highlighted as your source.



> B. I could and eventually will write a book, but it will involve all aspects of fitness/nutrition/drugs/supplements/contest prep/personal training/gym ownership/and more. You can go read the 3 articles that I wrote for MMI to see whether they were cut and paste, or go ask the CEO of VPX why he headhunted me out of thousands upon thousands of people in the industry to head up his websites, write for the magazine, write ad copy, and represent the company at seminars and other functions.



You mention the magazine and supplement company like i care?

I fail to see your point by illustrating that you write for a magazine i don't like (and know many others who don't) and work for a company i certainly don't care for. In fact, i can think of only two people on all the boards i frequent who actually like VPX - you and BigSwole.



> C. I crack up at the thought that "I" need more schooling to learn to comprehend what I read, as I'm sure that I have more knowledge in my small toe than you have in your entire head.



Well you said it, so it must be true.



> I also find it sooo hilarious that you need to bring "backup" with you everytime you want to get another wasteful point across.



I invited no one over here. I just know Fortified Iron's name and that he runs a message board. He sent me a PM after i posted asking who i am.

However, all this matters little because it doesn't alter the fact that the "science" behind your article is completely flawed and inaccurate.


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## gopro (Jun 26, 2003)

TCD...I am utterly dissapointed with myself that I even bothered to respond to your childish posts. I promised myself I would not waste my valuable time with any of the nonsense you post here at IM, and I broke it! Shame on me. Anyway, I haven't totally figured out what your psychological/emotional problem is, but I don't know that I want to go to such a dark place. 

I will from now on ignore you and everything you say as I would any child with an attitude problem, and I hope that all others will do the same (if they know what is good for them).

Regardless, have a nice life TCD. I hope you eventually grow up, learn respect, and recognize your own insecurities, so that you can be a productive member of society.

(oh, and if you have any respect left and wish to respond to me, do it in a PM so that we no longer destroy this poor guys thread)


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## Robboe (Jun 26, 2003)

Well, you sure told me with that post, Eric.


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## FortifiedIron (Jun 26, 2003)

> _*Originally posted by Snake_Eyes *_
> Pretty much, yup.
> 
> The true oxidative type I fibers have exceedingly high fatigue thresholds.....I can't see a set short of 50-100 reps doing anything for the vast majority of them.



Its the amount of tension placed on the muscle by the load. There is more tension on  muscle with 55% of 1rm then there is on a muscle during hte course of a mile run. More tension, The contraction velocity and strength are much more different meaning with the higher tension the quicker fatigue happens.


Kc


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## Snake_Eyes (Jun 27, 2003)

Those are also different fibers 

As in, they'll all contract. But the fatigue times are so high on most of the type I fibers, if they aren't under tension long enough they don't get fatigued.

Increasing the load doesn't help because those fibers can't generate the force required to lift it. All you're doing is recruiting fibers with a higher recruitment threshold and fatiguing those instead.

Anything short of 3-5 minutes isn't going to significantly affect the vast majority of the true type I oxidative fibers. Weight training and indeed any form of short-term anaerobic work is going to predominantly train the IIa and IIx fibers. In longer bouts of work, some of the type I's with lower fatigue times may be trained, but by and large they aren't.


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## FortifiedIron (Jun 28, 2003)

Ok, I see what your saying now and It makes perfect sense to me now.  Thank you bro, learn something new every day!


Kc


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