conversion of slow twitch to fast twitch (repeat?)

i posted a little profile thing here a couple months ago, but I never had anytime to come back till now (summer). anyways…

well, i didn’t see anything about this in sports sciences so I’ll just ask (if this is somewhere else, could someone kindly give me a link? or a general location…)

is it possible to “convert” slow twitch to fast? or say you were born 50-50 or a little slow twitch dominant. with proper training, could you still become a decent sprinter/jumper? Or is it possible to be a decent, 5:30-ish miler, while a decent sprinter?

just wondering, because I’m still not sure what I am. I’m an incoming sophomore, 15 years old, 5’5, chinese kid who plays soccer. My mile was a 5:45, which isn’t too bad, and my 400 was a 56-57, which isn’t too bad either (though not exactly a sprint). My standing vertical leap is about a 25", and running is a 34" (i’m hoping I can dunk after i hit 5’7-5’8 and put on some muscle).

So basically here’s my situation: my “slow-twitch” times are okay, but my “fast-twitch” numbers aren’t bad either. I know at my level (I haven’t really been able to train/workout for 8 months or so because my knees were giving me all sorts of problems), it’s still hard to tell whether i’ll be an explosive short distance or long distance guy. But do I actually have a choice? Or is my slow-twitch fate sealed?

ill be as honest as i can be by saying to go for the event which gives you most pleasure,have fun with what you decide!

Good advice from x-man. If I had a penny for every athlete who was told that he can’t do this or is too big, too small, too this or too that and then went on to prove them wrong, I’d have a lot of pennys!

Worry about the things you can control (training program, nutrition, skill development, etc) and the rest will fall into place. The only way to find out if you have the genetics to excel at something is to put everything you have into it. If you fail, then at least you have no regrets. It’s about the journey not the destination.

People told me I would never go sub-11 or make it to state and look at me now…ANYTHING can happen, as long as you put your ALL into what you want to do then nothign can stop you.

I have had a similar question and I was wondering if EMS could possibly help in this situation. In CFTS, he says that in young athletes(how young?), EMS trains the transitional muscle fibers to take on the characteristics of fast twitch because EMS preferentially recruits fast twitch muscle fibers first.

So, could using EMS help?

Did anyone notice that the kid didn’t get an answer to his question; re muscle fiber conversion?? Hello? Anyway, I have not studied the subject, but I do recall in DB Hammer’s writings, he mentions a theory of muscle type conversion based upon the theory that the muscle type is “wired” if you will, at the CNS level. In other words (I am sure I am butchering the theory but hope he gets the jist and it will encourage further research), how the CNS is trained dictates the ultimate muscle fiber type. That is the “theory” in a nutshell. I do not know the relative merits, if any, of the science, or lack thereof, behind this theory. However, I think it answers your basic question; yes, there exists at least one theory that I’m aware of, that proposes that fiber type can be “converted”.

The other points by the posters are absolutely valid, albeit not necessarily an answer to the basic question. Do not impose limits upon yourself. I can give you some examples of my own.

I’m 6.1 Caucasion. Growing up, I wanted to play football. Grandfather, mother, etc., all said I was too skinny, that I’d never be a “big” guy, wasn’t built like that, so no future in it. Well, given that I accepted that and eventually fell in love with basketball, the “big” theory was never tested. However, post basketball retirement, I get into powerlifting. I am not 275 w/relatively low BF. So, of course I could have played football.

As a younger basketball player coming up, was drilled into my head that white guys couldn’t jump, bla bla bla. Bottom line? At age 18 or so, I’m 38-40 vertical touching top of square (11 feet). I could go on and on. The point is, these guys are right; do not impose limitations upon yourself. The human will is the most powerful weapon the world. To understand that statement is to begin to rule the world. Harness your will. And pursue the event that makes you happy. Sometimes the biggest determinator in ultimate performance, in my opinion, is the committment of the athlete to the goal. Committment is another word for “will”. But, I believe it was a chinese proverb that said you will not catch any rabbits if you pursue too many. :slight_smile:
Will has no power if it is not focused upon something.

Good luck to you.

read the question again steve and break it down.there are numerous questions being asked in the initial post so please don’t be sarcastic.thanks x-man

Excepting some fairly non-physiological approaches, such as reversing the innervating motor neuron (i.e. taking a type II motor neuron and attaching it toa Type I fiber), it doesn’t look like you can convert a Type I to a Type II fiber or vice versa. So while Hammer is correct in general (neural impulses do appear to ‘set’ the fiber tpe and MHC isoform), conversion from one type to another doesn’t appear to occur under normal training circumstances.


thanks for all the input. I guess you’re right…I’ll never know till I try.

And I was talking to my gym teacher the other day (who has a phd in this stuff), and he was talking about the nerve stuff that you did. He actually told me about this alleged experiment where scientists took mice, cut open their bodies and hooked their muscles to electrical charges and stuff. They “shocked” them (much more complicated and technical than that, of course) and in doing so (correctl) converted all the muscles to fast-twitch properties.

of course, the mice couldn’t do squat after that, but still…

but I guess there’s no normal way through traditional training methods to convert slow to fast?

EMS would help probably by selectively recruiting, and with the correct settings on a quality unit, hypertrophy fast fibres in muscles. You can still run fast with 30% fast fibres if you are able to increase your fast fibre diameter to approximately 2.5X their physiological size. In other words, through purposeful training, you can increase your portion of 30% for example to equate to a man with 70% fast fibres. It is possible. The recent relative success of 400m Polish sprint relay team has been attributed to this phenomenon. They are not blessed with an abundance of fast fibres but they have been successful in increasing the fast fibre cross-section they have, to equate to others who have a larger percentage of fast fibres.

so how do u selectively hypertrophy fast twitch fibres

I’d imagine it would take a long time and you would have to be dedicated to a program geared toward that. What the program would be, I’m not exactly sure.

So you might get that fast twitch hypertrophy over time just by including EMS in your training, as recommended by Charlie(No more than 15 treatments in each phase, with 10x10sec on 50 sec off)?

sorry, but what exactly is EMS? some electrical shock stimulus thing?

oh, and as far as making a 30% fast twitch person becoming, in essence, a 70% fast twitch person…wouldn’t it be quite hard to maintain the proportion of the sizes of fast to slow twitch? And aren’t slow twitch fibers always recruited first? I don’t know all too much about this, so please excuse my ignorance…

And correct me if i’m wrong (i’m probably wrong), but isn’t hypertrophy usually associated with your fast twitch converting to slow twitch? I understand that to some extent, size converts to strength/speed/explosiveness but when do you know you’ve hit the limit (to the point where the size is hindering your explosiveness/killing your fast twitch)?

I believe EMS stands for electro muscle stimulation or something like that. Its basivcally electric shock and there a bunch of different protocols for treatment. Its used to treat injuries, but there is also talk (as you see here) about using it to recruit fast twitch muscle fibers.

As far as hypetrophy, it just refers to a growth in the size of the fiber. Hypertrophy is not limited to any fiber type, and can happen to all types of muscle tissue. The hypertrophy that you might be thinking of that would limit explosiveness and power would be structural hypertrophy as opposed to functional hypertrophy. Functional hypertrophy would be an enlargement of the actual myofibrils in the tissue, whereas structural hypertrophy would be an enlargement of the nonworking parts of the muscle tissue (heres where I get confused with the sarcomere and the z-line and whatnot).

My understanding, yes. You can, the human body is incredible. A man with 30% fast fibres can train and take on a man with 70% fibres if he trains purposefully and with dedication and increases muscle cross section. Correct me if I am wrong about her name. Bonnie Blair the American speed skater only had 20% fast fibres but was olympic champion at a sport that demanded a “higher” percentage of fast fibres. This probably suggests that her fast fibres had compensated by increasing cross-sectional area.

We can all take heart and count on the fact that our bodies will adapt if given the correct stimuli.

Ultimately, a proper sequence of training followed year in year out will take care of selective hypertrophy.

Correct. However, relative to Type II fibers, Type I have a far smaller ability to grow. Hypertophy of Type II fibers is mainly a matter of imposing progressive tension demands (with a damage component on them).

The hypertrophy that you might be thinking of that would limit explosiveness and power would be structural hypertrophy as opposed to functional hypertrophy. Functional hypertrophy would be an enlargement of the actual myofibrils in the tissue, whereas structural hypertrophy would be an enlargement of the nonworking parts of the muscle tissue (heres where I get confused with the sarcomere and the z-line and whatnot).

You’re probably thinking of growth of stuff like the sarcoplasm, glycogen/water stores, etc. Makes you look bigger but doens’t really lead to performance improvements. Keeping the weights in a more intensive zone (80% 1RM or higher) should avoid non-functional hypertrophy for the most part.


The problem in general with discussions about conversion of st to ft fibers (other than to gain a theoretical understanding) is that it is slightly off-focus for an athlete. The goal of an athlete is performance. Yes, as part of achieving greater performance, the ft/st profile of various muscle groups may shift (or it may not) but the goal is not increasing the % of ft. The goal is to improve performance.

I think we are using % of ft as a proxy for performance, but I’m not sure this is well established. Bonnie Blair is a great example. Also, as mentioned above, DB hammer makes the case that the real focus should be on the nervous system since it dictates the characteristics of the muscle fibers. I would prefer to focus on establishing the proper training protocols for performance and let the ft/st % sort themselves out.

but say you have a precious few strands of fast twitch fiber to begin with…if you go about training wrong for a sport that NEEDS explosive movements (basically every ball sport), then you’re in trouble. I wanted to know so I had a better “perspectives” on my chances at excelling alongside my perhaps more genetically gifted teammates…

that tad about bonnie blair is really interesting/encouraging though :stuck_out_tongue: thanks

so i’m going to start training/lifting on wednesday. in order to “selectively” hypertrophy fast twitch fibers, would I still go about with a 3x8 or 4x8 routine to build basic strength/size?

oh, and approximately how long would it take your fast twitch to degenerate into slow twitch fibers…is this a short process or something that takes place over a long time?

Do not worry so much about fast fibre conversions and fibre type at your level too much. Just train smart. Selective hypertrophy will happen over time as you train. Follow the CFTS you can’t go wrong its tried and tested, you won’t have to re-invent the wheel. Follow the sequence and adapt to your needs but keep the general ethos of the plan.