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Everything You Need to Know About Muscle Fibres

Our muscular system is a complex and intricate network of carefully woven fibres that come together to move our organs involuntarily and to move our limbs on a whim.

Shirtless man with towel over head and toned stomachEach muscle is made up of cells known as muscle fibres. Clumps of muscle fibres form the organs in our bodies and the masses under our skin that many people take an interest in strengthening and bulking.

Strength training is the best way to increase the volume of individual muscle fibres to create the bulky, toned physique that many people desire.

To better understand how to work and build our muscles, it can help to understand muscle fibres and the different types in our bodies.

Five Things to Know When it Comes to Muscle Fibres:

  1. Types of Muscle Fibres
  2. Types of Skeletal Muscle Fibres
  3. Common Issues with Fibres and Prevention
  4. How to Increase Muscle Mass
  5. Which Muscle Supplements can Help

Types of Muscle Fibres

Within the body, there are three kinds of muscles and, therefore, three types of fibres:

  • cardiac muscle
  • smooth muscle
  • skeletal muscle

Each type of fibre serves a role depending on the location in the body.

Cardiac Muscle Fibres

Realistic detailed drawing of heart

As the name would suggest, cardiac muscles are found only in the heart. They are striated, meaning striped in appearance. This striping is due to the thick and thin filaments that create the shape of each muscle fibre.  

Cardiac muscle fibres are unlike any other muscle in the body because they have pacemaker cells that control the heart’s contraction.

In addition, the cardiac muscle fibres are interconnected and branched, so when the pacemaker cells cause the heart to contract, the impulse spreads in a wave-like pattern.

These features work together to facilitate the constant and regular beating of the heart. As you could probably guess, these muscles function involuntarily, without you thinking about them.

Smooth Muscle Fibres

Smooth muscles are named for their smooth, uniform appearance. They are not striated, and they are found in the internal organs and eyes.

The fibres are much shorter than striated muscle fibres and are oblong. Like cardiac muscles, smooth muscles function involuntarily and carry out functions like changing the size of your pupil depending on lighting and moving food down your throat and through the digestive tract.


Running skeleton figure in front of pink background

Skeletal muscle fibres are the ones we’re typically thinking about and exercising with strength training. They are connected to the skeletal system and control our conscious movements.

Each skeletal muscle comprises hundreds or thousands of long, thin muscle fibres. Hundreds of thousands of myofibrils comprise each muscle fibre, which are all tightly joined together by connective tissue. This creates the striated appearance like the ones in cardiac muscles.

Skeletal muscle fibres are classified in different ways based on the way they generate energy.

Types of Skeletal Muscles

Type 1

These fibres are darker in color due to a higher number of mitochondria—the energy generating part of a cell. Type 1 fibres use oxygen to generate the energy it takes to move.

Type 2A

These fibres are lighter in color due to fewer mitochondria. Type 2 fibres also use oxygen for energy.

Type 2B

These fibres do not use oxygen for energy and instead store energy for short, quick bursts of movement. In addition, these fibres have fewer mitochondria than type 2A fibres, making them appear white.

Fast-Twitch and Slow-Twitch Muscle Fibres

You might hear different types of muscle fibres referred to as fast or slow-twitch muscles, especially when talking about exercise. Type 1 are slow-twitch fibres, and types 2A and 2B are fast-twitch.

Woman smiling while doing cobra position on yoga mat

These names refer to how quickly a muscle contracts, which depends on how quickly the fibre can act on adenosine triphosphate (ATP).

Fast-twitch fibres act on ATP up to two times as fast as slow-twitch fibres. Each fibre serve its own purpose. Fast-twitch fibres are used for short, explosive movements like in sprinting or strength training. Slow-twitched are utilized for sustained activities, from holding posture to endurance training like distance running.

While everyone’s bodies contain cardiac, smooth, and skeletal muscles, the amount of slow-twitch and fast-twitch muscles varies greatly from person to person.

In general, your typical activities influence the amount of fast or slow-twitch fibres. Lots of endurance training leads to more slow-twitch fibres while lots of strength training leads to more fast-twitch.

Muscle Fibre Issues Relating to Exercise

Now that we understand the muscle fibres we’re discussing when we talk about exercising, let’s talk about common muscle fibre issues and injuries resulting from exercise.


Muscle cramps happen when a muscle contracts involuntarily. They can occur in a single skeletal muscle fibre, or a whole group of fibres

Woman holding cramping foot on yoga mat next to tennis ball and towel

Common causes include:

  • overuse
  • dehydration
  • strain
  • holding one posture too long

While cramps can be rather painful, they generally resolve themselves within minutes.

Sprains, Strains, and Pulls

Muscle strains, also known as pulls, happen when damage occurs to the muscle or the band of tissue that attaches the muscle to the bone. Sprain injuries refer to damage to the bands of tissue that connect two bones together.

Strains occur when the muscle is stretched too far, usually as a result of:

Wrapped hurt foot walking on dirt
  • overuse
  • improper form

These kinds of injuries can be painful and cause lingering pain for a long time. Mild strains tend to resolve themselves within six weeks, while severe strains can take several months.


If a muscle is severely overstretched, it can tear. Tears can happen slowly over time because of overuse, or they can happen suddenly. The same things that cause strains can cause tears.

Tears are typically very painful, take months to heal, and, in severe cases, may require surgery.

How to Prevent Muscle Fibre Issues

Obviously, it’s ideal to avoid any and all muscle fibre issues while you’re training. Whether you enjoy endurance training, strength training, or a combination, these problems will slow down your intended progress.

You can do several things to prevent injuring your muscles:

  1. Stay hydrated and drink water throughout your workouts.
  2. Warm-up your muscles before you begin a workout.
  3. Always prioritize form, whether you’re strength training or endurance training.
  4. Cool-down your muscles at the end of your workout.
Two men drinking cold plastic bottles of water on summer day

In addition, contrary to popular belief, stretching before or after your workout does not reduce your risk of injury. However, you should still make stretching a part of your exercise routine, as stretching does improve and maintain flexibility, which is important especially as we age.

How to Build Muscle Fibres

Many people that strength train do so to increase their muscle mass. By strength training, you’re actually increasing the filaments that make up each muscle fibre. This increases overall muscle mass.

There are three parts to increasing your muscle mass, and all are of equal importance:

  1. Strength training
  2. Nutrition
  3. Recovery
Woman flipping tractor tire on track

You need nutrients from your diet to sustain your body through your strength training (carbs) and then repair your damaged muscle fibres while you heal (proteins). Your body also needs all the micronutrients from your diet to carry out these processes.

Strength training is the stimulus that signals your body to produce more muscle fibres. The type of fibres the body synthesizes is dependent upon the exercises you do.

Recovery is essential because it takes time for your body to heal the damaged fibres and create new ones. The body cannot complete this process if you never take a rest day.

To understand how these processes occur, let’s further discuss what happens to the muscle fibres while you are strength training and endurance training.

What Happens to Muscle Fibres when Strength Training?

During strength training, each time you lift a weight, the muscle contracts. The heavy stimulus causes microscopic damage known as microtears to the myofibrils that make up the muscle fibres. This happens mainly in the fast-twitch muscle fibres.

The tears stimulate the body’s repair response, which brings the necessary nutrients to the fibres via the bloodstream. The repair process heals the damaged fibres and synthesizes the growth of more myofibrils.

Strength training causes an increase in the myofibrils within the fibres, not more fibres themselves. The increase in myofibrils increases the fibres volume, leading to the plump look you’re going for. 

What Happens to Muscle Fibres when Endurance Training?

Man running with resistance parachute on beach

During endurance training, like distance running, the slow-twitch fibres are used instead of fast-twitch. Endurance training modifies the fibres used and helps them become more efficient.

Endurance training typically increases the number of mitochondria and myoglobin. Both features help to increase the storage of oxygen and ATP production.

As you can see, all muscle fibres are necessary. However, if you want to tone or build muscle, strength training is more promising than endurance training alone. Now let’s talk about the nutrition piece of the puzzle.

Muscle Supplements that Help Build Muscle

We mentioned that the damage caused to the fibres during strength training triggers the body to send nutrients to the cells and begin repairing and synthesizing more myofibrils. Without the necessary nutrients, the repair process cannot be carried out successfully.

The most critical piece of nutrition for building muscle is protein. Athletic, active people require 1.2-2.0 grams of protein per kilogram of body weight. Protein goals can be reached with a combination of whole foods and muscle supplements.

These are the most effective muscle supplements to support the growth and repair of muscle fibres:

  1. Protein Supplements
  2. Amino Acid Supplements
  3. Creatine
  4. Mass Gainers

Protein Supplements Help Meet Protein Goals

Beyond Isolate Whey Protein Supplement Superstore

Protein supplements are by far the most popular muscle supplement. With anywhere from 10-30 grams of protein per serving, protein supplements make it easy to consume the necessary protein to meet your nutritional goals and ensure your muscles can synthesize new fibres.

Protein supplements also make it easy to consume protein immediately following a workout, which can help switch the body out of the damaging catabolic phase and into the building synthesis phase.

Amino Acid Supplements Offer Nutritional Insurance

Ans Quench BCAA Supplement Superstore

Once we consume proteins, our bodies break them down into amino acids. There are nine amino acids, known as the essential amino acids (EAAs). They are named such because we must consume them in our diet; our bodies cannot create them the way it can produce nonessential amino acids.

All nine essential amino acids are required for something to be considered a complete protein. Without these, the body cannot carry out all the necessary functions required.

Amino acid supplements are growing in popularity in the muscle supplement category. They’re a great way to ensure you’re getting all the EAAs so that your body can efficiently synthesize new myofibrils and heal the damaged ones.

Creatine Helps You Work Harder

Allmax C:VOL creatine Recovery Supplement Superstore

Creatine is a well-researched muscle supplement, but it’s not nearly as popular as it should be. This is one of the rare supplements that can benefit people whether they work out or not, and it has numerous health and fitness benefits ranging from increase strength and endurance to more muscle mass to better brain health.

Creatine is a relatively easy supplement, too, as there are no time requirements on when to take it, just take it daily.

Mass Gainers Provide Excess Calories and Carbohydrates

Hulk HD Protein Weight Gainer Supplement Superstore

Mass gainers are an alternative to protein supplements—they’re essential beefed-up protein supplements. These muscle supplements offer the necessary carbohydrates and calories to boost you to a calorie surplus if you’re looking to pack on the most muscle.

Building new muscle does require excess calories. While you can still tone your muscles without increasing your calories, you can achieve results much easier if you modestly increase calories and protein together.

Mass gainers can offer between 250 and 1000 calories per serving and often contain anywhere from 30-60 grams of protein. Therefore, it’s a good idea to look at the nutrition label when selecting a mass gainer and chose one that best fits your macro needs.

Growing your muscles can be an intimidating goal but learning about muscle fibres can give you better insight into why strength training and nutrition matter. With a little hard work, lots of rest and recovery, and a closer look at your muscle supplements, you’ll be well on your way to achieving your goals.

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