Determining if you're fast twitch?

With skin folds? How valid is this? From latest issue of T-mag.

"Today’s training tip comes from Strength Coach Don Alessi:

You can actually estimate your dominant muscle fiber type by using skin folds. If your suprailliac fold is greater than your abdominal and mid axillary folds, then you’re most likely fast twitch.

If that’s the case, you should focus mostly on low-rep training and avoid meals that contain too many carbs. In other words, the majority of your sets should consist of fewer than 5 or 6 reps and you should make an effort to ditch the potatoes, bread, and sugar cookies whenever possible.

Note: Measure the suprailliac fold by taking a diagonal pinch just above the hipbone at the anterior axillary line, which is an imaginary line down the front of the body where the arm inserts into the torso.

Measure the mid axillary fold by taking a vertical pinch on a vertical line descending directly from the center of the armpit at the level of the xiphoid process, which is the bony nub "

Since the purpose of skin folds is to find out the distribution of fat to determine which range your Body Composition falls in, how does skinfolds determine fibre type?

I would be quite skeptical in his theories, although, like any good coach/scientist, you should never dismiss the fact that it is possible that there is something to what this guy is saying. All I can say is, being in the industry myself, I haven’t heard that before.


sounds like BS to me…

I have put on weight and remained fast twitch and have gotten down to ~5% BF and remained fast twitch. I don’t get it? :slight_smile:

I think it has more to do with where the fat is. I wonder what the reasoning is behind these two spots.

Although not directly related to this discussion, and interesting article on the role of hormones and regional body fat storage can be found here:

I dont think it matters where you do skinfolds, in those two spots or anywhere else for that matter. We are dealing with apples and oranges here, fat is fat and muscle is muscle.

I wouldn’t worry about Fasttwitch%, the CNS is more important IMO

You can be 80% fasttwitch and have a slow CNS, then you’d be a good BB’er but not someone who is explosive or fast :slight_smile:

Fasttwithc or slowtwitch it doesent really mean anything. All contractions are controlled by the CNS so if fast impulse is sent to a slow fiber it will act like a fast one. Either way sprinting is a action that is dependent on reactive elastic components ie. tendons, fascia.

James Colbert, your assertion is not entirely correct. Force production capabilities are relative to fiber diameter. The greater the cross-sectional area the greater potential for force production.

Type II fibers are inherently larger than Type I, thereby, capable of producing higher force output.

Thus, all else being equal (training parameters and so forth), the power development athlete who is type II dominant will always have an advantage over a type I dominant individual.

This fact has been illustrated through muscle biopsies taken from sprinters vs. marathoners which shows that (at the world class level) sprinters posses type II dominance, in contrast to marathoners who possess type I dominance.


I support what you said. I do believe that you should be type II dominant in order to make it to the end. But then I still don’t believe in that genetics can stand in your way. So I wanted to ask whether there was range for conversion. I mean can we ( using specific training ) convert type I fibers to type II fibers and vice versa?? I believe we can.

I want to add that strength training generally causes fast fibres to become slow. Speed/sprint training causes fast fibres and slow fibres to becomes fast oxidative fibres. Genetics determines how many of your fast and slow fibres will be converted to fast oxidative; and what direction of fibre conversion you can achieve. Strength training is essential because of the increase in cross-section of muscle. Goes without saying that sprint training is essential and fundamental.

Check out the thread below:

:eek: I used to believe that strength training convert from slow to fast!!! Come on. Let me ask you another question that might be more important. Why do you always get all kind of answers for a specific question?? For example, if I ask a group of exercise experts what is more important? exercise1, exercise2, exercise3, exercise4 or exercise5. a group will say exercise1 and another would say exercise2 and so on. Even thought they are all experts!!! Doesn’t that happen here as well. When ever you put your hand on something that you could call a fact, it comes out to be that others ( who are very high standard as well ) believe in the complete opposite. Please, please can someone explain. Does that mean that we have a 100 ways to reach the very top. Does this mean that every coach ideas are only specific to a group of people while it would not work on others. I mean that would mean that track and field ( and specially the sprints ) is a very very very complex issue where you would keep studying forever and never get all you want. :confused: :confused: :confused:

I think he means converting IIB to IIA which is slower, but still, you do convert I to II…or at least I think so.

Not so much.

That’s a function of training, IMO, more than it is innate characteristics. Marathoners and sprinters train differently, as should be obvious to everyone. FT units are larger that ST units only if they’re trained.

The literature suggests more and more that muscle fiber typing, in terms of the MHC expression, is very plastic and very adaptive in response to training. The only hardwired variances are in the FT/ST classifications, very general.

The nervous system is going to be the dominant variable as always. I’m not sure where this idea of a “slow” CNS comes from. It either fires or it doesn’t. About the only allowances in that arena are how aroused you are, how efficient you are at recruiting fibers quickly (explosive strength), and technique issues (intermuscular and intramuscular coordination). All of which are trainable or otherwise controllable.

There are genetic factors that can limit someone’s progress, but fiber composition just isn’t one that I’d consider to be valid.

I guess I read something hear written by Charlie that said that warming up elevates your body tempreture. Which in turn reduces the resistance of the neurons. Which makes the puls come faster. Doesn’t that mean that if we increase the cross sectional area of the neuron we reduce the resistance permenantly??? Can we do that?? And if we can, to what extent??

Look for these on Pubmed:

Deschenes MR, Judelson DA, Kraemer WJ, et al. Effects of resistance training on neuromuscular junction morphology. Muscle Nerve. 2000 Oct;23(10):1576-81.

Deschenes MR, Maresh CM, Kraemer WJ, et al. The effects of exercise training of different intensities on neuromuscular junction morphology. J Neurocytol. 1993 Aug;22(8):603-15.

Deschenes MR, Covault J, Kraemer WJ, Maresh CM. The neuromuscular junction. Muscle fibre type differences, plasticity and adaptability to increased and decreased activity. Sports Med. 1994 Jun;17(6):358-72.

Deschenes MR, Will KM, Booth FW, Gordon SE. Unlike myofibers, neuromuscular junctions remain stable during prolonged muscle unloading. J Neurol Sci. 2003 Jun 15;210(1-2):5-10.

PowermanDL, I have read many sources as of late that approximate what you stated in your post.

Noting that the training stimulus yields fiber type conversion. I feel that it must also be noted that although, for instance, a type I fiber may assume the characteristics of a type II fiber (by way of specific training) the type II fibers also respond to the specific training parameters and therefore develop greater force production values than the type I counterparts.

So I hypothesize that if a type I dominant individual and a type II dominant individual, both who are untrained and possess equal biomechanics, tendon insertions, etc., are simultaneously introduced to a short sprint training protocol, the type II dominant individual will continually out perform the type I dominant individual in the short sprints because of a greater response to the training stimulus.

Do you agree?


Thanks powerman. That was really helpful. I’ll get down and start reading now.

When I discovered these truths over five years ago at Loughborough University, United Kingdom. I was dismayed, this did not fit in with what I had been lead to understand and believe, the conlcusions I made wrongly at the time probably hampered my development as an athlete. I now realise that you can use this info to your advantage. With anything in life you have advantages and disadvantages.

The advantages of strength training far out weigh the disadvantage of the fibre conversion to slow twitch isoforms. Increased selective hypertrophy of fast fibres more than slow, muscle synchronisation, increased glycolysis and other energy substrates, to name a few. What you must take on board is the fact that different types of strength training are less fibre converting to slow than others. For example, repetition aka body building training leads to hypertrophy with a large transformation of fast isoforms to slow isoforms
Max strength leads to the some fast to slow isoform expression BUT not as much as body building. Speed-strength training (emphasis on intra rest between repetitions of medium to high loads, includes plyo and body weight excersises) leads to slow to fast conversion, unloading (decrease) in volume of strength training aslo leads to faster fibre expression. What is fascinating is that rest helps the CNS to recover and so leads to fast isoforms being expressed again.

The East Germans knew about this way way back and probably most of the Eastern block. They discovered that to increase max strength by a larger amount, cross-sectional training must precede max strength followed by speed-strength speed or speed endurance. So the fibres would first convert to slow isoforms, then stabilise during the max strength phase, then convert to fast oxidative with conversion from slow and fast glycolytic during speed-strength, speed or speed endurance training respectively. The wrong sequence of training will lead to the wrong adaptations.

If you look at CF’s training, it follows the correct fibre conversion process.
At the beginning you do cross-section training then move onto max strength and when max strength finishes, speed work volume increases with speed endurance whilst strength training loads are maintained or decreased in volume.

What must be understood (along with the undeniable fact that muscles are very plastic), is the direction of muscle conversion and the sequence of training activities. Those who are very talented probably will express a larger amount of muscle mass that expresses fast isoforms EVEN after training regimen that would lead to slow conversion for the not so fortunate. The key is to sequence training properly to achieve the right muscle fibre expressions at the right times. Muscle fibre conversion MUST be understood for max performance. Also very very heavy volumes of training are detrimental to the CNS leading to fast to slow fibre conversion.

In short any exercises that are phasic to ballistic in training with adequate recovery and reasonable volume will help you to express more fast isoforms. Tonic exercises are likely to lead to slow fibre expression.

Do not worry so much about fast fibre percentages, because you may not express the elite sprinters’ fibre profile at this moment in time, but your body may be very trainable and plastic, leading to some slow fibres expressing fast isoforms after the correct sequence of training and fast fibres remaining fast but developing more endurance.

This seems very complex but the key is the correct training done in the correct sequences.

Those who are very talented probably will express a larger amount of muscle mass that expresses fast isoforms EVEN after training regimen that would lead to slow conversion for the not so fortunate.

Yep - See this in football all the time. Survival of the fittest.