The Different Types of Horse Muscle Fibres and Why They Count

When we look at a horse, and see the muscles rippling, we are often led to think of what the horse represents to humanity. Many associate horses with speed, grace, strength, and wisdom, but how many of us have taken the time to look at what makes the horse able to maintain these symbolic ties to our culture?

What does the horse look like beneath its skin? How are its muscles grouped, and what makes them able to combine strength with speed, making one of the most loved and useful animals in our culture, across the board?

Under the Skin


Although it might be expected that the muscular system of the horse would be very complex, in all reality, the muscles of the horse’s body are built of only two main types of muscle fibres. With the mixture of these two main types of muscle fibres, the horse manages to exude extreme speed, and strength, which are very important in our relationship with them, on an inter-species level.

To make them even more useful, horses are known for their quick minds, and high intelligence, so we find in horses, a strong, fast, and intelligent companion, unlike any other species.

Type I

So what is the first type of muscle fibre that is involved in the muscular make up of the horse? The first type of muscle fibre is known as Slow Twitch fibres. These are also widely known as Type I fibres.

The Slow Twitch fibre is responsible for giving a horse its endurance. These types of fibres are like small power plants, providing the horse with energy that will enable it to run long distances without tiring. The American Quarter Horse is known for having a high number of Type I fibres.

Type II

The Second type of muscular fibre is a fast twitch fibre. This fibre is also known as type II. This fibre type is known for giving the horse bursts of speed. This fibre type is subdivided, into two distinct sub types. Type IIA and Type IIB.

The first is able to create energy to be utilized during times that require endurance, but is also required for the horse to maintain high speeds, and/or repeated jumps. Type IIB is mainly for those times when a strong burst of speed is required to help the horse maintain high speeds, at different times throughout a race or jumping situation.

The Irrelevant Breed Debate

As you can see, the horse is a built intricately, and is perfectly suited to its uses by humans. The Type I muscle fibres enable the horse to run long distances without feeling fatigue, they even go so far as producing more energy to be used by the horse, while it is running. The Type II fibres, although able to produce smaller amounts of energy, truly excel at letting the horse reach and maintain maximum speeds.


These two types of muscular fibres in horses work together to make the animal the best it can possibly be. There is a definite difference in the dispersal of these muscular fibres amongst the various horse breeds. The Quarter Horse, known for its awesome ability to herd cattle over impossibly long distances, is known to have more Type I fibres, leading to its excellence at endurance, whereas the Arabian horse is known to have fewer Type I fibres, and more Type II fibres, leading to its ability to maintain extreme speeds for long periods of time.

The Andalusian is another breed noted for its high endurance, and ability to keep a mind bending pace on the track. As you can see, the debate of which breed is better than the other is truly irrelevant, as the breeds of horses each have their own skill set, at which they excel.