Types of muscle fibers - red and white fiber differences

Types of muscle fibers - red and white fiber differences

Types of muscle fibers - red and white fiber differences
Types of muscle fibers - red and white fiber differences

Science recognizes two types of muscle fibers: red (slow) and white (fast). The ratio of muscle fiber types is one of the parameters that distinguishes a top sprint athlete from a marathoner.

Knowing what types of muscle fibers work with exercises is useful not only for improving performance, but also for the capacity of the athlete. Thus, it is useful for choosing  methods  of muscle recovery .

Ignorance of the physiology and  muscular genetics  of the body makes a person choose the wrong training strategy. To gain lean muscle mass and sculpt an athletic body; It is necessary to understand how the muscular system works and what types of muscle fibers predominate.

Differences between red and white muscle fibers

Human muscle consists of connective tissue, capillaries, sarcoplasm and both types of muscle fibers. The latter, in turn, are divided into white (fast) and red (slow) fibers. The contraction rate at which they work is the main difference. The color differs due to the source from which they absorb energy.

Slow muscle fibers (red) are responsible for maintaining homogeneous, static and lasting loads; this type uses fat as the main source of energy. Fast muscle fibers (white) have the function of making short but high-intensity movements; They use  muscle glycogen  and  creatine  for energy.

How do you know if a muscle fiber is slow or fast?

An example of how to distinguish between the two types of muscle fibers is to make an analogy with birds. For example, chicken breasts and wings; They are characterized by their white color and minimal presence of fat. The thighs and legs have a characteristic darker color of red muscle fibers.

Most of the time the birds are on the ground, where the muscles of their legs withstand constant static load. This load is absorbed mainly by slow muscle fibers. (1)  On the other hand, the muscles of the wings are used for short and intense movements. This type of movement is made by fast fibers.

There is a greater presence of slow muscle fibers in the stabilizing muscles of the torso, spine, internal abdominal muscles and leg muscles. In the other areas, fast muscle fibers predominate  (3)  .

Slow / red fibers

Slow muscle fibers are thin and weak. They can withstand loads for long periods of time. Its reddish color is due to the presence of oxygen molecules. Oxygen is essential for fat oxidation. Proper transport in the body requires iron.

On  aerobic exercises  such as running or walking, as slow muscle fibers. One of the main things when performing this type of exercise is to keep the heart rate in the fat burning area (60-70% FCM). In this way, oxygen is delivered to all muscle tissues.

The best exercises for targeting red muscle fibers are  static exercises  . Abdominal boards and fixed squats are the most classic exercises.

Fast fiber / white

In order for fast fibers to work, high-intensity movements are required. To move, muscles need quick access to some source of  glucose  . Fats are useless for the work of this type of muscle fibers. It takes at least a few hours to transport and oxidize. Ideally, the energy should come from a place that is accessible and very close to the muscles:  muscle glycogen stores  .

White muscle fibers are used to perform explosive movements, they work on the basis of glycogen and phosphocreatine adenosine triphosphate (creatine phosphate or PCr)  (2)  . The increase in muscle volume is mainly due to the growth of these types of muscle fibers.

The proportion of muscle fibers depends on the somatotype of the body

The human musculature consists of a network of different types of muscle fibers and this depends on the  somatotype  of the body.

The good news is that the body is able to adapt to regular exercise and slightly modify the ratio. Of course, this depends on the sport that is practiced. In the case of a marathoner, the percentage of slow muscle fibers can reach 80% of the total. On the contrary, fast fibers predominate in high-intensity athletes.

How to exercise fast fiber?

Strength training is best for exercising fast muscle fibers. The greater the weight to lift and the smaller the number of repetitions, the better the fast muscle fibers will be processed.

The main energy source for this type of muscle fiber is glycogen. That is why it is important to consume a sufficient amount of carbohydrates. Especially before and after a routine workout. This is the reason why there are often athletes who charge energy with fruit  after a workout  . It is not only protein that is important in sports nutrition. Oatmeal with fruit is an example of an ideal pre-workout breakfast.


  • There are two types of muscle fibers: white (fast) and red (slow) muscle fibers.
  • Each type of fiber uses different energy sources to generate muscle movement.
  • The ratio of muscle fiber types can be changed with exercise.
  • Strength training acts on white fiber, before doing this type of exercise it is recommended to consume the appropriate dose of  carbohydrate foods  .
  • Slow muscle fibers are activated by performing long-term, low-intensity aerobic exercise.
  • The  ratio of carbohydrates, proteins and fats  should be based to provide energy for both types of muscle fibers.


  1. Muscles - Fast and slow twitch,  source
  2. Skeletal muscle,  source
  3. Speed ​​and power training,  source
  4. Fast Twitch, Slow Twitch…. Who exactly are you? source
  5. Classifications of human skeletal muscle fibers. source