Fast and slow shrinking fibers

It has happened to all of us that in a sports discipline, no matter how much we train, we may find someone who with less effort surpasses us in certain actions, such as distance running, speed … without finding an apparent reason. Relax, this has a scientific explanation and it happens because of our physical constitution. We all have biological characteristics that predispose us genetically to have more or less performance in what activities according to these are more focused on resistance or immediate work of strength and power.

In order to determine that in which activity there will be greater possibilities of becoming a great talent, we must study the differences between the different types of muscle fibers. There are two types of fibers:


• Slow shrinkage fibers, red or oxidative: these fibers are long and pale, this color is due to the slow shrinking fibers have a high content of myoglobin (hemoglobin), these fibers tend to be more abundant in the muscles responsible of activities of low tension but great continuity (background), in contrast we have.

• Fibers of fast contraction, white or glycolytic: they predominate in the muscle used when it is necessary to develop great forces, they are fibers as the name indicates of fast contractions, powerful and of fast fatigue, predominate in the athletes that compete in activities of force speed and short duration.

While it is true that both fibers are used in all sports disciplines, a bottom athlete can reach a percentage of slow contraction fibers of up to 82% compared to 70% of white fibers that sprinters can count on.

According to research studies we conclude that fast-twitch fibers experience greater fatigue than slow-twitch fibers.
Here is a clear summary of the differences between the two fibers:

Rapid Shrinkage:

• A low aerobic capacity
• A high glycolytic capacity (lactic acid)
• Low capillary density
• A large force of contraction
• High fatigability
• A large distribution in athletes who do not engage in endurance tests
Slow shrinkage:
• A high aerobic capacity
• Low glycolytic capacity (lactic acid)
• A high capillary density
• A small force of contraction
• Low fatigability
• A large distribution in athletes engaged in endurance activities
In future articles I will indicate what kind of exercises we should perform according to the fibers we want to stimulate.

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