Difference Between Fast and Slow Twitch Muscle Fibers

If you are a fan of sports or fitness, you have probably heard of people having different types of muscle fiber. Some even say that athletes that have slow or fast muscle fibers may have an advantage in some sport due to the specific type of muscle fiber.

This advantage comes from the different response to training techniques. If they are properly targeted, these fibers can make your muscles extremely efficient and powerful.

This article goes over the difference between fast and slow twitch muscle fibers, describing their specific types and the techniques for training all of these types.

How Do Muscles Work

Muscles have many great functions. They allow internal organs to operate and they allow the movement of all body parts. Muscles make up almost 40% of your total mass. You have more than 600 muscles in your body, which are all built from a sort of elastic tissue.

Muscles are fueled by food, or adenosine triphosphate (ATP) to be precise. The metabolic process produces ATP which is further transformed into mechanical energy by muscle cells.

Every muscle is made up of thousands and thousands of tiny muscle fibers. These muscle fibers are made of small strands of fibrils. If you are wondering about their size, muscle fibers are only 40mm long.

Muscle Types

Muscles are divided into cardiac muscles, smooth muscles and skeletal muscles:

Cardiac Muscles

This type of muscles is only found in the heart and their function is heartbeat regulation. They work non-stop, and they do it automatically. Cardiac muscles cause the heart to fill up with blood by relaxing and they make it squeeze out blood by contracting.

Smooth Muscles

Smooth muscles are in charge of bowel movement, these are named visceral muscles. They also regulate the movements of the arteries, hollow organs, heart and stomach. You can also find these muscles in the bronchi, bladder walls, and skin. Like cardiac muscles, they work automatically, without our knowledge or control.

Skeletal Muscles

Humans use skeletal muscles to control the limbs and external body parts. They shape the body while covering the skeleton. Each skeletal muscle in the body has a twin muscle on the opposite side.

Your body has around 320 bilateral muscle pairs. Movement is carried out by contraction of one muscle and expansion of its par. Muscles are connected or attached to the bones via tendons. Our joints are stable because the tendons extend over them.

You move skeletal muscles consciously, unlike the previous muscle types which move automatically. You can also see most of these movements. The motion is made by skeletal muscle contractions, and it can be movement of the fingers, arms, head, eyes, mouth (as in talking) and legs (as in running and walking).

Skeletal muscles are in charge of keeping a good posture. Also, they prevent joints from dislocating, and they even control our facial expressions. Finally, skeletal muscles are involved in maintaining body temperature by releasing heat after their contractions and relaxations.

Types of Muscle Fiber

Skeletal muscles contain lots of muscle fiber called myocytes, made up of many myofibrils. Myofibrils are protein strands (myosin and actin) which are responsible for muscle contractions. Muscles get shorter when they contract, which is a result of myofibrils grabbing and pulling each other.

Muscle fibers can be divided into two basic types, slow twitch muscle fibers (also known as type 1) and (type 2) fast twitch muscle fibers. Muscle fibers type 2 can be divided even further into types 2a and 2b.

The difference between fast and slow twitch muscle fibers is in their ability to impact the muscle response to various types of physical activity. Every type of muscle fibers contracts in its own manner, which is what makes it special. The ratio of slow and fast muscle fibers is determined by genetics, but usually, they are 50-50 even.

Slow Twitch Muscle Fibers

Slow twitch muscle fibers are great for prolonged muscle contractions because they are better at generating ATP fuel with oxygen use. This means that they can maintain the force for a longer period of time, but the amount of force is not that great.

These slow twitch fibers are activated first during muscle contraction because their point of activation is very low. Fast twitch fibers are only activated if the type 1 cannot generate enough force necessary for some activity.

If you do regular endurance training, you can improve the density of mitochondria, the organelles that are responsible for making ATP in an oxidative reaction. In turn, you will generate more adenosine triphosphate.

You can find a lot of slow twitch fibers in the tonic muscles which are in charge of posture maintenance.

Fast Twitch Muscle Fibers

Fast twitch muscle fibers are more suited for producing shorter bursts of speed or strength because they get fuel from anaerobic metabolism. The amount of force they produce is greater than slow fibers, but fast muscle fibers also fatigue faster.

Type 2a fibers are also called intermediate fast twitch muscle fibers because they depend on both energy sources and anaerobic and aerobic metabolisms.

Type 2b fibers are the standard fast twitch muscle fibers as previously mentioned.

Fast twitch fibers have a high density in the phasic muscles that are used to generate movement. These fibers can affect muscle size and definition. It is no coincidence that power and strength exercises increase their density.

Final Advice for Training both Fast and Slow Twitch Fibers

Fast twitch fibers are better for sports that require explosive and strong movements. A good way to engage them is resistance training with lots of weight. Perform the exercises with fewer repetitions but higher weights. Rest for around 90 seconds between reps.

Slow twitch fibers are better for sports which require endurance. Use lighter weights for resistance training but at higher repetitions. You can also practice circuit training with minimal rest to engage these fibers. Your body weight is enough for this type of exercise if you do many reps.

 

References:

https://www.acefitness.org/education-and-resources/professional/expert-articles/5714/slow-twitch-vs-fast-twitch-muscle-fibers
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4039363/

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