What is The Difference Between Slow Twitch and Fast Twitch Muscle Fibres?

Personal/Fitness Training Blog

Why is it that some people are best at running marathons or cycling for hours but can hardly perform a box jump? Ever wondered why others can jump very far or high, or sprint exceptionally fast, but cannot run very far? Well, the difference lies in the make-up of their skeletal muscle, specifically their muscle fibres.

A Muscle is Made Up of Various Muscle Fibres

In turn these are made up of many fibrils. Skeletal muscle fibres are identified as:

  • Slow-twitch muscle fibres (type 1)  which allows us to run marathons and cycle far – any endurance type of exercise, and
  • Fast-twitch muscle fibres (type 2), which allow us to exude a lot of power in a short amount of time  but fatigue very quickly and are activated in exercises like plyometric jumps and sprinting.

All muscles contain both slow- and fast-twitch fibres. The determining factor is how much of them are present in the muscle itself. For example, more slow twitch fibres mean a person will perform better in endurance-type exercises and activities. Fast-twitch fibres mean a person will be better at explosive, short bouts of exercise like sprinting and jumping.

How Do Muscle Fibres Work?

During aerobic exercise, slow-twitch muscle fibres are the first to be contracted and engaged. Generally, because slow-twitch fibres can provide their own source of energy, the endurance of slow twitch-fibres is high so we are able to perform exercise at a steady state for some time.

However, slow-twitch muscle fibres cannot generate large amounts of force. Once these become fatigued and the force becomes too much for them to handle, fast-twitch fibres are recruited and engaged. These then take over. Aerobic exercise increases our level of fitness, stamina and the muscle’s oxygen capacity. This allows the body to burn energy for longer periods of time.

Fast-twitch fibres are broken down into two categories

  • Moderate fas-twitch fibres are thick, quicker to contract but wear out more rapidly than slow-twitch fibres.
  • Fast-twitch muscle fibres are low in endurance but can generate a lot of force in a short amount of time. These fibres have a high threshold and will take over from slow twitch fibres when the force required is too much for slow-twitch fibres to handle. Although fast-twitch fibres generate more force, they fatigue sooner than slow-twitch fibres and are also responsible for the size and definition of a muscle.

What Type of Workout Engagages Which Type of Muscle Fibres?

Aerobic exercises, bodyweight exercises with high repetitions and resistance training with lighter weights may all engage the slow-twitch fibres in the muscle, allowing you to increase your fitness and endurance.

Fast-twitch fibres are engaged with strength and explosive power-type workouts. Weight training with heavy weights engages the fast-twitch muscle fibres. As the weight increases, more fast-twitch fibres fibres are recruited and engaged. Explosive, power-based workouts will recruit greater levels of fast-twitch fibres . However because fast twitch depletes energy levels so quickly, they also require longer periods of rest.

Determining the amount of slow and fast twitch fibres that your muscles are made up of will assist you in understanding the type of training you need to do to reach your goals. A simple fitness test should give you an indication of the makeup of your muscle fibres after which you will be able to implement a suitable training regime. Want to know more about how to develop a training regime? Trifocus Fitness Academy’s Personal Training Certification will help you get there! Click here for more information.