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). The 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 musculature of the body, and white (working on glycogen) – in the musculature of the limbs. How do these types of muscle fibers differ 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 at the same time. 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 work on free fatty acids – while sprinters and weightlifters have a predominantly fast type that requires glycogen.
In fact, the ratio of fiber types affects how easily the body will 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 muscle fiber types in a particular person is determined both by his physique and regularly practiced physical activity. Runners have well-developed red muscle fibers, while jumpers and sprinters have white ones.
Ectomorphs, who are naturally thin, usually have no problems with being overweight – but it is difficult for them to gain muscle. Endomorphs and mesomorphs are distinguished by good strength indicators, however, the endomorph is 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 the difference in muscle fiber types is the meat of chicken or other poultry. The breast and wings are white and have minimal fat, while the legs and thighs are dark red in meat and have a higher fat content.
Since the chicken most often stands, the muscles of its legs experience a constant static load – the main work is performed by slow muscle fibers. In contrast, the muscles of the wings are used exclusively for short, but vigorous flapping – the load goes to the fast type of fibers.
Slow (red) fibers
Although the slow fibers themselves are quite thin and weak, 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 serve as the main source of energy for slow fibers.
That is why aerobic training and long-term cardio are ideal for losing weight – in fact, such loads involve slow muscle fibers and force the body to burn fat reserves. However, the main role is played by the total duration of the load.
Fast (white) fibers
For high-intensity explosive loads, muscles require rapidly 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 primarily on glycogen (that is, muscle carbohydrate stores), ATP and creatine. At the same time, we recall that muscle growth and an increase in musculature as a result of strength training are largely due to an increase in energy reserves.
How to determine which fibers you have more?
In reality, the human musculature always consists of a plexus of muscle fibers of various types. In the stabilizing muscles of the trunk and spine, the internal muscles of the abdomen and in the muscles of the legs, slow-type fibers usually predominate, while in other skeletal muscles, fast-type fibers.
However, under the influence of regular physical training, the athlete’s body is able to adapt. Studies show that marathon runners have more than 80% of all muscle fibers are slow – in contrast to sprinters, in which fast fibers predominate, amounting to about 65-70%.
Workouts for muscle growth and weight loss
For training fast muscle fibers, hypertrophy training is best – strength exercises performed in the range of 6-12 repetitions. The higher the working weight and the lower the number of repetitions (and the less time under load), the more actively fast muscle fibers are involved in the work.
In contrast, to burn fat and engage slow muscle fibers, both static loads and monotonous cardio performed for at least 30-45 minutes are needed. Plus, such workouts are especially effective when blood glucose levels are low – this will force the body to focus on fat reserves.
Muscle fibers are divided into fast and slow. Strength training recruits fast (white) fibers, requiring carbohydrates and glycogen, while recruiting slow (red) fibers and burning fat requires prolonged low-intensity aerobic exercise performed for at least 30-45 minutes.