Fast Or Slow-Twitch Muscle Fibers

How do you know whether or not you have more fast-twitch or slow-twitch muscle fibers?
Are some people born with more of one or the other? Does how you train decide that?

You could have a sample of your muscle tissue analyzed under a microscope. Otherwise, just determine what kind of training gives you the best results. The more fast-twitch fibers you have, the more you’ll grow on explosive low reps with heavy weight. More slow twitch means you’ll need to work more with moderate weight and the typical 6-12 rep hypertrophy range. Never neglect variety and periodization in your training as a result of your genetics in this regard, though.

Look at Don Alessi’s article about reactive training (either this issue or last, not sure). He recommends using the vertical leap as a test for muscle fiber make-up.

In T-mag 186 there is an article by Don Alessi called Reactive Strength, it discusses using vertical jump as a way of measuring muscle fiber type and a way to test.

With all due respect to Mr. Alessi, how is a vertical jump supposed to tell you your fiber make up in muscles like your delts, pecs, bis, tris? The fact is, that it can’t!! No multi joint movement can tell you your fiber composition…it is plain foolishness. Fiber composition can vary from muscle to muscle, thus single joint movements can give you the best idea (outside a biopsy).

thanks everyone!

Ian king wrote an article on it.
He mentioned many different types of test (although he didnt say how to do them if I recall correctly)Then he said why they were crap said that Vertical leap was a GOOD test gave a very long description as to why (although didnt cover hiters reason as to why not). Then he went on to say that its pretty silly anyway and that everyone should train to become more fast twitch.
Youll need to do a search for the article

There is no conclusive scientific proof that one can change one fiber type to another; the studies tend to show this cannot be done.

no, fiber types may not convert, but they may take on the behavioural characteristics of other types.

So everyone has slow and fast twitch muscle fibers in ALL muscle groups? Assume I train each muscle group 2x per week. What would you think of training the first three days with 4-6 reps (fast-twitch) and the second three days with 8-12 reps (slow-twitch) for 6-8 weeks? Makes sense to me.

As far as fiber type…genetics plays a huge role. However, quite a bit of research has been conducted and some conclusions have been drawn. With resistance training, there is a shift from IIB to IIA and also with extensive endurance training II fibers can be converted to I fibers–although it is likely that the II fibers just take on I characteristics than change. I fibers cannot be converted into II fibers though.

for all intents and purposes Fibers can change types. THere isnt any realy IIB in humans rather IIX (IIB is the kind in animals…). Your training will influence your muscle fiber types.

vj, yes everybody’s got both “types” in every muscle, but in reality muscle fiber occurs on a continuum of differing fiber types, specific to their location and function. There aren’t just 2 or 4 “types,” there are many more. I’ve even read recently of a new fiber “type” that athletic coaches are looking to manipulate through gene therapy called “X Fibers.” These apparently are faster twitch than any other, but are dormant in most people.

There are two ways I know of to assess this. One is a muscle biopsy, which you’d be stupid to perform unless you have a big reason to know. Or you could test yourself. I caution though, that testing using exercises like I’ll describe isn’t all that accurate and is influenced by training history. Take your 1RM of whatever main exercise for whatever muscle group you’re interested in. Then take 80% of that weight, and see how many times you can lift it with the same form. If you’re under 5, the test indicates that you’re predominantly fast twitch. Over 8… slow twitch. In all honesty though, does it really matter? You can already find out which muscle groups tend to be fast twitch, like the short head of the hamstrings, biceps, and gastrocnemius. Particularly slow twitch fibers tend to come in the soleus, long head hamstrings, forearms, and in certain abdominal muscles. Hope this helps.

The reason I asked is because I’m having a hard time building my pecs.

I have a very hard time feeling tension in my pecs when performing incline, decline, flat benches and flies. My chest muscles look like 1/4 inch thick. My ribcage is round instead of flat (my dad has a round ribcage too). Could the roundness of my torso mean I should do different types of exercises to build my chest?

I think i have more fast twitch muscles. When I was in high school, the weight lifting coach told us that if our muscles were short and wide we had fast twitch and if they were long and skinny (width) we had short twitch. (Please set me on the right track).

Thanks for your help in advance

unless i am some sort of enigmic paradox, the vertical jump stands to tell nothing about fiber composition. i run a legitimate 10.9 100m dash, yet my vertical jump is a mere 24.5 inches. since both sprinting speed and jumping ability supposedly gauge fast twitch compositon, what the hell gives here?

DOUG SANTILLO: I think I come in at the under 5 reps catagory (but I will have to test this to be 100% sure). How should I change my training, I usually aim for 8-12 reps to failure, is this appropriate for somebody with my fibre makeup? Also, when I train for strength, I use 5 reps (not to failure). Is this the most optimal rep-range for me to be training in? Thanks for ur time bro…

to Stan: if you really have a good reason to believe you’re fast twitch in a certain muscle group, it should still have only a marginal impact on how you train. Sure you can shift your rep ranges down a bit for any particular workout phase you’re in, and certainly 5 reps under failure is too light a load for a strength phase for anyone. This probably means you’re lifting about your 7RM. An average trainee should generally be using about their 4RM for pure strength training, and a seasoned veteran will get more benefit from going as high as even their 2RM for many, many sets.

To VJ: If you’re having problems with your chest development, their are other issues to consider other than your fiber type. Look first to your exercise form, sequence, priority, and volume before you go after smaller issues like fiber make-up. If you’re really having a problem with chest development (as opposed to simply not liking your genetic structure), start using some pre-fatigue exercises before your compound movements, and for a few weeks, go very slow on the concentrics while concentrating on firing your pecs. In other words, try a 416 tempo on bench presses, and while you’re going up to the count of 6, focus your mind on squeezing your chest together. Once your nervous system learns to recruit your chest in compound movements, you can return to normal speeds and exercise sequence. This should get your chest up to speed…

Most people say that there is no way to change fiber type. This is because that fiber type is a test for the amount of mysoin Atp-ase in the cell this is an enzyme that brakes down atp. but this does not test for other cellular changes such as capillary density, mitochindra density,aerobic enzymes so there are ways to change the body at the cellular level but very little change in myosin atp-ase

Thanks Doug…I’m starting the GVT 2000 program in January. I’ll follow your tempo instead of the 402 tempo suggested in the article.
Thanks again for your time.