Oct 23

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Muscle Fiber Types And Bodybuilding/Determining Your Dominant Fiber Type!

Our muscles are made up of 3 different types of muscle fiber.  The slow twitching muscle fibers, the Type 2A fast twitching muscle fibers and finally the Type 2b fast twitching muscle fibers.  Each one of these muscle fibers have their own unique characteristics and help us with different types of activities.

Type 1 Slow Twitching muscle fibers are used in most of our daily activities as well as sporting events such as long distant running , for example 5 K, 10 K etc…  This type of muscle fiber is capable of using oxygen in a nice steady pace and are fatigue resistant even though they have a very minimum force output.

Type 2 A (Fast Twitching muscle fibers) have a much higher force output, however these fibers have a much less oxidative metabolism capability which means that they are not nearly as resistant to fatigue.  A good example would be the 400 meter run, which takes about 43-45 seconds at the Olympic level.  This could be comparable to the DTP training method (Drastic Transformation Principle)  created by Kris Gethin.  This method is performing an exercise 50 reps  rest- 40 reps -30 reps -20 reps and 10 reps ……  During the 50, 40, 30, even 20 rep range we are mostly using the 2A muscle fibers which also has a huge role in building dense muscle tissue.

Finally, the Type 2 B (Fast Twitching muscle fibers) have the highest force output and also the most susceptible to fatigue.  A great example would be the 100 meter run, which is 9-10 seconds at the Olympic level, 50 yards swimming and 1-8 rep range of heavy weight lifting.  This type of muscle fiber is the best for strength and power so as bodybuilders its is crucial to use this type of fiber for hypertrophy by training heavy with low reps!


There is actually only one accurate way of finding out the dominant muscle fiber type of an athlete.  (It requires a muscle biopsy where a needle is stuck into the muscle and a few fibers are plucked out to be examined under a microscope.)
The second and less invasive method is using a compound exercise such as the Bench Press.  This is probably the choice most of our readers are interested in…

STEP 1:  Figure out your 1RMs, one repetition max on the given lift.
STEP 2: Calculate the 80% of your 1RM.
STEP 3: If you can do fewer than 7 repetitions, then you have more than 50% fast twitching muscle fibers. If you can perform 12 or more reps, then your muscles are composed of  more than 50% slow twitching fibers. And finally if you can perform between 7-12  then you have a pretty equal rate of muscle fiber types.

To make the above statement clear, if you are able to do your 80 max more than 12 reps this means that your 1 rep max is probably not much, due to the lack of high force output fibers which is the TYPE 2 Fast twitching fibers and in most cases you probably would have a less bulky and more of a smaller and leaner look such as a marathon runner!  JUST REMEMBER WE WOULD NOT EXPECT AN ELITE MARATHON RUNNER TO BENCH PRESS 500 LBS because of the way he/she looks and because of the simple fact that he/she is lacking the power/strength muscle fibers.

Because lifting weights requires the use of many muscles at once, this method will not work for individual muscles, but only those muscle groups. In order to determine the fiber-type composition of an individual muscle, a needle biopsy of the muscle of interest must be performed.


Unless you are striving to be an endurance athlete, training the TYPE 2A and The TYPE 2B muscle fibers should be your priority in order to achieve muscle gains.  And it is highly recommended to keep tricking the muscles into new growth by using plateau breaking techniques such as negatives, drop sets, super slow reps as well as heavy straight sets in order to assure that you are recruiting both the A and B side of the Fast twitching muscle fiber types.

Melih F. Cologlu  ACPT
Unleashed The Beasts Editor In Chief
Team Grenade Athlete

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