Increase Muscle Growth with Specific Muscle Fiber Training

Muscles are made of 2 different types of fibers and by knowing your personal muscle fiber composition you can design a workout specifically customized for each muscle. But how do you know what muscle fibers a particular muscle has? Working your muscles the wrong way will result in decreased muscle growth because not enough muscle fibers are activated.

Each muscle consists of 3 types of fibers: slow twitch (type 1) and fast twitch (type 2A and type 2B). The amount of different fiber types in each muscle can help you determine how to train each muscle group in a decent way.

Different Muscle Types

Based on functional and structural characteristics the muscle tissue of our body is divided into skeletal muscle tissue, cardiac muscle tissue and smooth muscle tissue. I won’t go very deep into cardiac and smooth muscles because these are not the type of muscles we want to focus on. Our main concern is the skeletal muscle tissue.

Skeletal Muscle

Skeletal muscle tissue is striated and can be contracted or relaxed by conscious control. It’s bound to our bones and it’s also the muscle type we’re after to increase in size as well as in strength. Skeletal muscle fibers vary in color depending on myoglobin contained in the muscle. Myoglobin binds oxygen inside muscle tissue helping to supply more oxygen to release energy needed for muscular contractions. Muscle fibers also contract with different speed which means fast twitch fibers fatigue faster than slow twitch fibers. This depends on their ability to split Adenosine Triphosphate (ATP). Faster fibers have better ability to split ATP as well as greater potential to grow in size and strength.

On this basis skeletal muscle fibers are classified into 3 types: type 1 fibers, type 2A fibers and type 2B fibers.

Type 1 Fibers

These fibers are slow twitch and contain plenty of myoglobin and lots of mitochondria and blood capillaries. Type 1 fibers are red and responsible for long duration, low intensity work like walking, cycling or any other aerobic activity. This fiber type splits ATP at a slow rate, is very resistant to tiredness, contracts with slow velocity and generates ATP by oxidative metabolic processes.

Type 2 A Fibers

Type 2 A fibers are fast twitch and contain very large amounts of myoglobin, more mitochondria and blood capillaries than type 1 fibers. Type 2 fibers have a fast contraction velocity, split ATP very quick, are resistant to fatigue and generate ATP by oxidative metabolic processes at very high capacity.

Type 2 B Fibers

Also known as fast twitch fibers these fibers contain little amount of myoglobin, few mitochondria and few blood capillaries. Type 2 fibers are white and fitted to generate ATP by anaerobic metabolic processes, contract at fast velocity, split ATP fast and fatigue easily.

Smooth Muscle

Smooth muscle tissue is found in lots of places like the tunica media layer of large and small arteries, stomach, intestines, bladder and some other places. Smooth muscle fibers aren’t striated like skeletal or cardiac muscle fibers and can’t be contracted by conscious control which means they are involuntary muscle fibers. Like skeletal and cardiac muscle, smooth muscle can experience hypertrophy (growth).

Cardiac Muscle

The majority of the heart wall is formed by cardiac muscle which are striated alike skeletal muscle fibers. But like smooth muscle, cardiac muscles also are classed as involuntary muscle so they can’t be contracted by conscious.

How to Determine Muscle Fiber Composition for a Certain Muscle

In order to determine the predominant muscle fiber type in a certain muscle we have to know the repetition limits of a muscle compared to its maximum strength. First you have to find out your 1RM (maximum weight you can lift only once) for an isolation exercise like dumbbell side laterals, barbell curls etc. You better stick to isolation exercises because compound movements involve several muscle groups which will distort results.

If you don’t know your 1RM you can use a 1 rep max calculator.

After figuring out your 1RM take 80% of this weight (multiply your 1RM with 0.8) and do as many repetitions as possible.

If you can do between 4–7 reps with 80% of your 1RM then you have mostly fast twitch muscle fibers in that muscle. The reason for this is that fast twitch fibers develop lots of strength but have poor endurance. You can lift more weight but you can’t get many reps out of it.

If you can do between 12–15 reps with 80% of your 1RM then your muscle fibers are mostly slow twitch which means they have great endurance but you can’t lift quite as much although you can a lot more reps with it.

A rep range between 7–12 reps indicates that muscle probably has an equal amount of fast twitch and slow twitch fibers.

By repeating this method for each muscle group you can customize your workout in order to develop your muscles to their maximum potential.

Well, as you know there are differences between individuals but there are also some resemblances in muscle fiber types in specific muscles. For example the legs, these mostly consist of slow twitch fibers as we walk every day on them so you’d be better if you train your legs with high reps (10 and more) but I recommend doing some heavy weight low rep squats to build overall strength.

Training Your Muscle Fiber Type

Working as many muscle fibers as possible is your goal when training with weights because the more muscle fibers are activated the greater are gains in muscle mass and strength.

If a certain muscle is mostly made of slow twitch fibers then you’ll have to train that muscle with high reps, short rest periods and high volume in order to get the most out of it. Slow twitch fibers recover fast, fatigue slow and need more work for maximum growth.

Quite disappointing could be the fact that slow twitch fibers have a very limited potential to grow so you make sure you also do some low rep training to work the fast twitch fibers in that muscle.

Maybe you have a lagging muscle which just won’t grow the way you want, the reason for that could be that the lagging muscle is mostly made of slow twitch fibers. More sets, higher reps (12-15, sometimes 12–20) and 30–60 seconds rest periods can speed up development of that muscle.

Don’t get the wrong idea with high reps because your weights should still be heavy so you reach muscle failure within those high rep ranges. Light weights won’t give a muscle a reason to grow properly.

You can consider yourself lucky if a muscle in your body consists of fast twitch fibers because they have a much greater potential to grow in size and strength while getting them to grow isn’t as difficult as it is with slow twitch fibers. The more fast twitch muscle fibers a muscle has the more it is likely to grow which means more muscle mass. Muscles of this type are the easiest to grow in size and strength.

Maximizing your fast twitch fibers in a particular muscle is done by using heavy weights, low reps (4–8) and resting for 90 – 120 seconds. Training volume (sets) should be moderate as too much volume will affect recovery.

For best overall development of a muscle group you should train both, your fast twitch fibers and your slow twitch fibers but focus on the type of fibers that makes up the majority. Working out this way will help you developing every muscle fiber type to its maximum.


Determining your muscle fiber composition can be helpful and makes sense although this method gives just a rough estimate. It allows you to work each muscle in a specific way required by the muscle so you’ll get better results from your training.

4 Responses to Increase Muscle Growth with Specific Muscle Fiber Training

  • medical assistant says:

    Great information! I’ve been looking for something like this for a while now. Thanks!

  • RedMango says:

    Very nice post!

  • Johnie says:

    Why do I bother calling up peolpe when I can just read this!

  • zoop williams says:

    I like the article, however you may want to try one small variation, when going heavy (2to3) rep sets try giving yourself 4 or 5 minutes between sets especially on large muscle groups. I am predominately a fast twitch guy (thank God) and have found that giving those muscles enough time for my ATP levels to build back up will allow them to continually push a maximum amount of weight over 3 to 4 heavy working sets and therefore achieve the greatest amount of hypertrophy, leading to the greatest amount of over-compensation.

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