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White muscle fibers

1. Fast muscle fibers

Skeletal muscle consists of two types of myocytes:

  • first type consists of slow-twitch muscle fibers (also red ones);
  • the second type is fast muscle fibers (also white ones), which, in turn, are divided into two subtypes (IIa and IIb). The second type of cells is the most important in bodybuilding, and we will talk about it in this article.

The ratio of skeletal muscle cells is mainly determined by genetics, and athletic potential of each person is largely depends on it.

Each muscle cell consists of many myofibrils - thin filaments of protein (actin and myosin) that can make contractions. Due to massive contraction of myofibrils the contraction of whole muscle is performed.

Type of fibers Speed of contraction Capacity for growth (hypertrophy) Speed of fatigue Used for Strenth Number of mytochondria Blood supply Oxydative capacity Glycolytic capacity Source of energy
Type I (slow) Slow Low Low aerobic activity (running, cycling) Low Many Abundant High Low Fats
Type IIа (transitional) Fast Low Moderate Prolonged anaerobic load High Many Moderate High High Creatine phosphate, glycogen
Type IIb (fast) Very fast High High Short anaerobic (strength training) Very high Few Poor Low High Creatine phosphate, glycogen

2. White muscle fibers

Quick muscle fibers (aka white) use anaerobic (oxygen-free) metabolism in the production of energy for contraction. They perform high-speed movements, which are characterized by large explosive power, but they get tired much earlier than slow ones. Both cell types produce roughly the same amount of work in a single movement, but white cells do that much faster.

There are two types of white muscle fibers: IIa and IIb.

Subtype IIa

Cells of IIa subtype are also known as intermediate or transitional. They can use both aerobic (accompanied by oxygen consumption) and anaerobic (anoxic) metabolism for energy production equally. These fibers are in the middle between fast and slow ones.

Subtype IIb

They are true fast muscle fibers, which can use only anaerobic metabolism, having maximum of strength and speed of contraction. These cells play major role in gaining mass in bodybuilding, so almost all the training programs are designed for development of this type of fibers.

White IIb fibers can get hypertrophic to a greater extent than slow ones.

2.1 What kind of sports fast fibers are important for?

It is this type of cells which makes a major contribution to achievement in those sports that require explosive power:

  • Weightlifting
  • Bodybuilding
  • Powerlifting
  • Martial arts
  • Sprint

2.2 How to train fast-twitch muscle fibers

  • Training program for beginners
  • Training programs for professionals
  • Also, do not forget about sports nutrition and diet for bulking up.

2.3 Genetics and Bodybuilding

Scientists have found that the ratio of fast and slow muscle fibers is genetically determined. The average person has almost equal ratio. The best results in bodybuilding are achieved by those athletes whose muscles contain more white fibers.

White muscle fibers are also important for sprinters, as fast muscle fibers always prevail in outstanding sprinters (about 80%).

There is evidence that featured workouts can affect this ratio. Strength training in bodybuilding can increase the number of cell of IIa & IIb types, while aerobic exercises increase the content of slow twitch cells (type I). However, these changes are quite limited. In studies it was discovered that transition from one type to another usually does not exceed 10%. For this reason, some people gain muscle mass with great difficulty, while others, on the contrary, very quickly.

2.4 How to determine the ratio of white fibers?

  • First of all, your progress in bodybuilding, powerlifting and other strength sports may indicate it. If all your efforts are in vain, then one can assume that slow fibers dominate in you.
  • Pass the test in the ratio of slow and fast fibers.
  • The maximum accuracy can be achieved by electromyography, which determines the exact ratio of cells in your muscles.

2.5 What to do if there are few white muscle cells?

If you want to get a fine figure and look attractive, this can be achieved even with white fibers in minority. Unfortunately, your achievements in professional sports will be small.

3. See also

  • Slow muscle fibers
  • Neuromuscular transmission
  • Propulsion unit of a muscle
  • Muscle cell
  • Contraction of skeletal muscle