Types of muscle fibers and the best exercises to train them

Approximately 40% of the mass of the human body is muscle. Each of the more than 600 muscles is necessary for us to perform vital functions: eating, breathing, walking, etc. In order for the muscles to be strong, they need to be trained. And to determine the correct type of training, you need to know that all the muscles of our body consist of two main types of muscle fibers, the features of which estet-portal.com will tell you about in this article.

Different muscle fibers – miscellaneous functions

Skeletal muscles are composed of two main types of fibers:

Type I fibers are responsible for endurance, type II fibers (fast, glycolytic, white) – for strength and speed.
Type II fibers begin to work when physical activity requires more than 25% of maximum force.

In most people, the ratio of muscle fiber types is approximately the same, and it is determined genetically. However, fast fibers are larger than slow fibers and have greater growth potential.

Genes determine three important factors in relation to muscle:

Maximum number of fibers.
Ratio of muscle fiber types.
Shape of fully engaged muscles.

The ratio of muscle fiber types is determined genetically, and the dominant type can only be identified through invasive muscle biopsy.

Next, estet-portal.com will take a closer look at:

features and exercises for training type I fibers;
features and exercises for type II training.

Muscle fibers of the slow (I) type: features of the structure and work

What you need to know about type I (slow) muscle fibers:

they contain mitochondria that use oxygen to produce the ATP needed for muscle contraction;
they are called red muscle fibers because they contain more myoglobin (oxygen-binding protein), which makes them darker;
because slow muscle fibers can provide their own energy, they can withstand small force loads for a long time, but are not able to provide significant force;
for this type of muscle fibers, a low activation threshold is characteristic, i.e. they are the first to be activated during muscle contraction; if they are unable to generate enough force to perform a certain action, fast muscle fibers are activated;
tonic muscles responsible for posture have a higher density of red fibers;
Static endurance exercise can increase mitochondrial density, which improves the efficiency of using oxygen to produce ATP.

Мышечные волокна медленного (I) типа

Which exercises are suitable for training slow type muscle fibers

The characteristics of slow muscle fibers and the features of their functioning allow us to determine the types of exercises that increase their aerobic activity. These exercises are:

isometric exercises (example: plank) that keep slow type muscle fibers in a contracted state over a long period of time – this increases the ability of these fibers to use oxygen to generate energy;
slow strength exercises with light weight but more than 15 repetitions in which aerobic metabolism is activated;
Circuit workouts in which one exercise replaces another almost without interruption;
body-weight exercises with high reps also increase the efficiency of the slow fibers;
when performing bodyweight or light weight exercises to train slow muscle fibers, it is best to reduce the interval between sets to about 30 seconds.

Slower exercises, multiple repetitions and light loads are suitable for slow muscle fibers.

Muscle fibers of the fast (II) type: features of the structure and functioning

Type II muscle fibers (white) are divided into type IIa and IIb fast fibers:

muscle fibers IIa (fast oxidative-glycolytic) use oxygen to convert glycogen to ATP;
IIb (glycolytic) muscle fibers use ATP from muscle cells to generate energy;
Fast muscle fibers are characterized by a high activation threshold, i.e. they are only activated when the slow fibers are unable to provide the required amount of force;
Type II fibers reach peak strength faster and can develop significantly more force than Type I fibers;
fast fibers are called white because they contain few capillaries;
white fibers get tired faster;
the phasic muscles responsible for movement are characterized by a high density of fast fibers;
fast fibers are responsible for the size and definition of certain muscles.

Which exercises are suitable for training fast-type muscle fibers

Based on the characteristics of fast muscle fibers, it can be concluded that explosive strength exercises and strength training are suitable for training them, namely:

heavy weight training stimulates motor units and activates more muscle fibers; the greater the weight, the more fast fibers are used to lift it;
explosive movements with weights or using own body weight – great way to train white muscle fibers;
Fast muscle fibers tire quickly, so to achieve maximum efficiency during the exercise, it is recommended to limit the number of repetitions to 2–6;
because this type of muscle fiber uses energy quickly, it requires a longer rest period (minimum 60-90 seconds between exercises) to recover.