There are three types of muscle fibers in the body of any person – slow red fibers and fast white fibers (they, in turn, are divided into two types). A key characteristic of each is the type of load supported – and the preferred power source.
Red muscle fibers (using triglycerides as energy) are predominantly found in the muscles of the trunk, and white ones (working on glycogen) are found in the muscles of the limbs. What is the difference between these types of muscle fibers and how to determine your type?
Types of muscle fibers
Muscle fibers are a unique type of physiological structure that has both strength and elasticity. They are divided into two types – fast and slow. Despite the fact that the fibers are usually intertwined, in professional athletes one of the types dominates.
For example, marathon runners and swimmers have a predominantly slow type of muscle fibers that works on free fatty acids – while sprinters and weightlifters have a predominantly fast type that requires glycogen.
In fact, the ratio of fiber types affects whether the body will easily withstand certain types of loads – both explosive power and monotonous anaerobic. Moreover, as a result of many years of performing certain exercises, the structure of the fibers can change.
Genetics and body types
Ultimately, the ratio of types of muscle fibers in a particular person is determined by both his physique and regularly practiced physical activity. Runners have well-developed red muscle fibers, while jumpers and sprinters have white ones.
Ectomorphs, naturally thin, usually do not have problems with being overweight – but they find it difficult to gain muscle. Endomorphs and mesomorphs are distinguished by good strength indicators, however, endomorphs are prone to gaining excess weight. In addition, different types of muscle fibers utilize lactic acid differently.
Fast and slow muscle fibers
The simplest example of a difference in muscle fiber types is chicken or other poultry. The breasts and wings are white and have a minimal amount of fat, while the legs and thighs are dark red in color and higher in fat.
Since the chicken is most often standing, the muscles of its legs are under constant static load – the main work is performed by slow muscle fibers. In contrast, the wing muscles are used exclusively for short but energetic strokes – the load is directed to the fast fiber type.
Slow (red) fibers
Although slow fibers are thin and weak by themselves, they can support physical activity for a long time. Their red color is due to the presence of oxygen molecules necessary for the oxidation of fats (triglycerides), which are the main source of energy for slow fibers.
That is why aerobic training and extended cardio are ideal for weight loss – in fact, such loads involve slow muscle fibers in the work and force the body to burn fat stores. However, the main role is played by the total duration of the load.
Fast (white) fibers
For high-intensity explosive loads, muscles require readily available energy. Fat is not suitable for these purposes, since its transportation and oxidation takes at least a few minutes. Energy should be in an easily accessible form as close as possible to the muscle fibers themselves.
For explosive efforts, the body uses fast muscle fibers that work mainly on glycogen (that is, on the stores of carbohydrates in the muscles), ATP and creatine phosphate ² . At the same time, we recall that muscle growth and muscle gain as a result of strength training is largely due to an increase in energy reserves.
How can you tell which fiber you have more?
In reality, a person’s musculature always consists of a plexus of muscle fibers of various types. The stabilizing muscles of the trunk and spine, the internal muscles of the abdomen and the muscles of the legs are usually dominated by fibers of the slow type, while in other skeletal muscles – fibers of the fast type ³ .
However, under the influence of regular physical training, the body of the athlete is able to adapt. Research suggests that in marathon runners, more than 80% of all muscle fibers are slow – in contrast to sprinters, who are dominated by fast fibers, accounting for about 65-70%.