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Types of Muscle Fibres: Fast-Twitch vs Slow-Twitch (Explained)

Updated: Aug 16, 2023

There are three major types of muscle and three muscle fibre types in the skeletal muscle system, each fibre type has specific usages and functions.


Some people have naturally higher ratios of specific fibre types, making them naturally better at one type of sport.


In this article, I'll explain the different types of skeletal muscle fibres and their functions and usages, and how some people may be naturally stronger, bigger, or have a higher endurance.


Table of Contents:



Types of Muscle

In your body, you have three different types of muscle tissue, as listed below.



Muscle fibres can be found in all of these types of muscle tissue. Below I'll go into more detail about each type of muscle.


illustration of muscle types

Skeletal Muscle

Hundreds to thousands of muscle fibres are firmly bound together by connective tissue in each of your skeletal muscles.


Smaller units made up of repeated thick and thin filaments make up each muscle fibre. The muscle tissue becomes striated, or striped, as a result of this.


There are two kinds of skeletal muscle fibres; type 1 and type 2. Type 2 is further subdivided into subgroups; 2a and 2b. I'll go into detail about these types of fibres further down.


Function

Tendons connect these muscles to your bones, and they regulate your body's voluntary motions and control posture. Standing, walking, leaning over, and picking up an item are all examples.



Smooth Muscle

Smooth muscles are not striated like skeletal muscles. Their name comes from their more uniform and smooth look.


These muscle fibres take on an oblong shape. They're also a millionth of the length of skeletal muscle fibres.


Function

Smooth muscles are involuntary, which means they are not under your conscious control. They are present in your internal organs as well as your eyes.


Moving food through your digestive system and altering the size of your pupil are two examples of their activities.


Cardiac Muscle

Cardiac muscles are striated in the same way as skeletal muscles are. They can only be found in the human heart and they have several distinct characteristics.


One difference of the cardiac muscle is that they have their own beat. Pacemaker cells are a special type of cell that produce the impulses that cause heart muscle to contract.


This is usually done at a steady tempo, but it may also be sped up or slowed down as needed.


Another difference is the fibres of heart muscle branch out. When the pacemaker cells produce an impulse, it spreads out in a wavelike manner, making it easier for your heart to beat.


Function

Cardiac muscle is a kind of muscle found in the heart. It's involuntary, just like smooth muscle. To enable your heart to beat, cardiac muscle contracts in a coordinated manner.



Types of Skeletal Muscle Fibre Types

Skeletal muscle is made up of three major types of muscle fibre, as listed below.


  • Type 1

  • Type 2a

  • Type 2b


Other subtypes, variations, and hybrid fibre types may also exist. (1)


You may be familiar with the terms fast-twitch (FT) and slow-twitch (ST) muscle. Types 2a and 2b are classified as fast-twitch, while type 1 fibres are classified as slow-twitch.


The terms FT and ST relate to the rate at which muscles contract. How fast a muscle acts on ATP determines the pace at which it contracts.


When the molecule ATP is broken down, it releases energy. FT fibres degrade ATP around twice as quickly as ST fibres do.


Furthermore, fibres that utilise oxygen to generate energy (ATP) tire more slowly than those that do not.


In terms of endurance, the following fibre types are ranked from best to worst: type 1, type 2a, then type 2b.


Slow-twitch muscle fibres are ideal for activities that last for a long time. Holding a posture and muscles that stabilise bones and joints are examples of this.


They're also utilised in endurance sports like marathons, cycling, and swimming.


Shorter, more intense bursts of energy are produced by fast-twitch fibres. As a result, they're great for tasks that need bursts of energy or power. Sprinting, boxing, and weightlifting are examples.


The features and characteristics of type 1, type 2a, and type 2b are compared in the table below.


Type 1

Type 2a

Type 2b

Contraction Time

Slow

Fairly Fast

Very Fast

Size of Motor Neuron

Small

Medium

Very Large

Resistance to Fatigue

High

Fairly High

Low

Activity Used For

Aerobic

Long-Term Anaerobic

Short-Term Anaerobic

Max. Duration of Use

Hours

<30 Minutes

<1 Minute

​Power Produced

Low

Medium

Very High

Mitochondrial Density

High

High

Low

Capillary Density

High

Medium

Low

Oxidative Capacity

High

High

Low

Glycolytic Capacity

Low

High

High

Major Storage Fuel

Triglycerides

Creatine Phosphate, Glycogen

Creatine Phosphate, Glycogen

As mentioned earlier, there may also be hybrid types of muscle fibres, such as a hybrid between type 2a and type 2b, sometimes referred to as type 2x muscle fibres.


However, there isn't a whole lot of research into how this occurs and why.



How Does This Affect People

Everyone's body is made up of both fast-twitch and slow-twitch muscles. Individually, however, the total quantity of each fibre type varies considerably.


Athletic performance may also be influenced by fast-twitch vs slow-twitch composition. In general, endurance athletes tend to have more ST fibres, while sprinters and powerlifters tend to have more FT fibres.


Some people may have a naturally higher composition of type 2b muscle fibres, making them stronger than other people.


Whereas other people may have a naturally higher composition of type 1 muscle fibres, making them better at endurance sports like swimming, cycling, and running.


How to Train Specific Muscle Fibre Types

Because these different muscle fibres have distinct characteristics, you can vary your workouts and training style, targeting specific muscle fibre types.


Once a certain training style is adopted your body and muscles will begin to adapt and slowly get better at specific workouts and sports.


For example, if you train for higher reps and cardio-based exercises, your body will recruit more type 1 and type 2a muscles


Some people combine different types of training, such as hypertrophy-strength hybrid training.


Hypertrophy Training (Type 2a Fibres)

Hypertrophy specific training is a training approach that is specifically designed to produce as much muscular hypertrophy as possible.


Although significant gains in strength are frequently observed when using this training method, it is not solely intended for strength gains.


The following are typical hypertrophy training guidelines:

  • 8-12 reps per set

  • 10 to 18 sets per workout

  • Eccentric based reps

  • Mostly single-joint, isolation exercises



Strength Training (Type 2b Fibres)

Strength specific training is a training method that aims to increase physical strength as much as possible.


Although significant increases in muscle growth are frequently observed when using this training method, it is not designed specifically for muscle size gains.


Strength training guidelines are typically as follows:

  • 2 to 8 reps per set

  • 15-30 sets per workout

  • Concentric/power based reps

  • Mostly compound/multi-joint exercises


Endurance Training (Type 1 Fibres)

Endurance specific training is a type of training that is specifically designed to improve muscular endurance.


Although some gains in strength or size may be obtained when using this training method, they are not intended for this purpose.


The following are typical endurance training guidelines:

  • 12-30 reps per set

  • 12-18 sets per workout

  • A medium-slow pace tempo

  • Mostly compound, multi-joint, and cardio based exercises


Further Reading



References

This section contains links to research, studies, and sources of information for this article, as well as authors, contributors, etc. All sources, along with the article and facts, are subjected to a series of quality, reliability, and relevance checks.

Real Muscle primarily uses high-quality sources, such as peer-reviewed publications, to back up the information in our articles. To understand more about how we fact-check and keep our information accurate, dependable, and trustworthy, read more about us.

This evidence-based analysis of muscle fibre types features 1 references, listed below.

1. Wayne Scott, Jennifer Stevens, Stuart A Binder–Macleod. Human Skeletal Muscle Fiber Type Classifications. Physical Therapy. (2001, Nov) ✔

Citations with a tick indicate the information is from a trusted source.

 

The information provided in this article is not intended to replace professional medical advice, diagnosis, or treatment. Always seek the guidance of a physician or other competent professional before following advice or taking any supplement. See our terms and conditions.



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