Muscle Fiber Types

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Muscle Fiber Types

Muscles. Did you know that we have more than six hundred of them in our bodies? Yes, most sources (both online and in books) say that there are over six hundred fifty known muscles in our bodies. Although some study states that they can go up to as many as eight hundred plus. It’s pretty cool, right? But, that’s not the only fact that makes our muscles amazing. Why? Because these muscles even have their own group so that they can work in an organized manner. Here, we will discuss the different muscle fiber types and how they function.

What are Muscle Fibers?

Muscle fibers are the cells that make up the muscles in our bodies, which facilitate body motion. They enable us to walk, move, and live. Our nervous system controls them, and they are the most distinctive characteristics that make us human.

What are the Major Types of Muscle Fibers?

There are three general muscle fiber types, and they are as follows:

1. Skeletal muscle fibers

These are the long muscle fibers that are voluntarily commanded, which means that we are able to consciously ‘command’ or control them. They are attached to our bones. Examples include our triceps and biceps.

2. Cardiac muscle fibers 

The autonomic nervous system regulates this type of muscle fiber -- the cardiac muscle fibers. If you haven’t heard about the autonomic nervous system, just think about your nervous system responsible for controlling involuntary movement. Examples of cardiac muscle fibers include the walls of the heart, hence the term ‘cardiac.’

3. Smooth muscle fibers

Smooth muscle cells make up the walls of our intestines, blood vessels, uterus (women), and the internal muscles of our eyes. Like cardiac muscle fibers, they are regulated by the autonomic nervous system.

What are the Subcategories of Muscle Fibers?

Our muscles are not just divided into cardiac, skeletal, and smooth muscle fibers. They are further distinguished into two categories: slow and fast-twitch fibers. Here’s a description of what they are and what they do:

1. Slow-twitch muscle fibers

marathon slow twitch muscle fiber types

Slow-twitch muscle fibers are also called type I muscle fibers. They use oxygen to function and provides continuous energy for muscle contraction. Even though these types of muscle fibers fire slowly, they have higher endurance.

2. Fast-muscle fibers

marathon fast twitch muscle fiber types

Fast-twitch muscle fibers, also known as type II muscle fibers, use anaerobic metabolism to function. Okay, so we used the word anaerobic here, and don’t panic. Anaerobic just means without air or oxygen. (Coined from the Greek words an- (no or without), aer (air), and bios (life).

Why Bother to Differentiate the Types of Muscle Fibers?

Now that you know the major categories and subcategories of muscle fiber types, you might ask, why is it important to know this stuff?

Well, here’s the reason why. By knowing these muscle fiber types and understanding how they differ, you’ll be able to know which muscles are used for your aerobic and anaerobic activities. Simply put, you will be able to configure and plan your training sessions or workouts according to your goals. For instance, if you are a marathoner, you can do exercises that focus on your slow-twitch muscle fibers. They have high endurance, and they provide continuous energy to the muscles. On the other hand, if you are doing sprints or activities that require short bursts of speed, you can focus on your fast-twitch muscle fibers.

To target a specific type of muscles, here’s the exercise for you:

Slow-twitch muscle fibers

For individuals who do marathons and aim to increase the endurance of their muscles, your training should include high volume, high frequency, and low-intensity repetition sessions.

Fast-twitch muscle fibers

If you are involved in anaerobic activities like sprints, you should configure your workouts session towards fast-twitch muscle fiber development. It requires a low volume, low frequency, and high-intensity repetition schemes.

muscle fiber types slow twitch fast twitch

By understanding these concepts, training sessions can be altered to increase the optimal efficacy of your training goals.


About the Authors:

Mike Zhang

Mike Zhang is the founder of the MZF Group. He graduated from the University of Toronto on the dean's list with a Masters Degree in science.  Mike was a two time National Muay Thai Champion, and a strength and conditioning coach to several learned athletes. He has over 14 years of experience as a Muay Thai Coach.

Marijune Tiamzon, RN, MHPNP

With nearly 5 years of experience in the medical field, Marijune holds a registered nurse license and a certificate as a mental health nurse practitioner. She is an adventurous young professional, and her hobbies include diving, windsurfing, and saber fencing.

As an avid writer, she is most passionate about sharing acquired knowledge in the medical field and how to apply it to improve the quality of life of our readers.