There are several types of muscle fibers. Type I, or slow-twitch muscle fibers, which have a relatively slow rate of contraction. They use predominantly aerobic metabolic pathways and contain many mitochondria with a high level of enzymes required for aerobic energy production (ie, enzymes required in the Krebs cycle and the electron transport chain), they have a higher capillary density to supply them with oxygen and energy substrates, as well as for the removal of by-products, for example lactic acid.
Athletes with a large number of Type I muscle fibers have a higher lactate blood threshold, because they can more quickly give pyruvate to the Krebs cycle and less pyruvate is converted to lactic acid, so they provide a sustained exercise and prolong the period of time before fatigue.
Type II muscle fibers, or rapidly shrinking, have a relatively fast rate of contraction and the ability to rapidly generate anaerobic energy. They are divided into categories, two of which are well defined. Type II muscle fibers have a high reduction rate and a fairly well developed aerobic and anaerobic energy production system. Type II muscle fibers are the fastest and most glycolytic. Most of the loads require a combination of fast and slow-contracting muscle fibers that can withstand relatively slow muscle contractions with occasional short jerks with rapid muscle contraction.
Loads that require the involvement of a larger number of type II fibers, such as sprinting, intensive walking, depend heavily on the accumulated carbohydrate stores. These loads are associated with a faster depletion of glycogen stores. The ratio of slow and fast-shrinking muscle fibers depends mainly on the genetic predisposition. In humans, an average of 45-55% of muscle fibers are slow-shrinking. However, training sessions can influence the distribution of types of muscle fibers. Athletes engaged in sports that require mainly aerobic energy (long distance running), slow-twitch fibers make up 90-95% of the working muscles.
Energy of chemical bonds of food accumulates in the form of fats and carbohydrates and to a lesser extent - in the form of proteins. This energy is transferred to ATP, which transfers it directly to the needy cell structure or compound.
Three different systems can be used in the transmission of energy ATP: pho-phagene, anaerobic-glycolytic and aerobic. Phosphagenic system transfers energy more quickly, but its ability is very limited. The anaerobic-glycolytic system can also transmit energy relatively quickly, but the products of this pathway reduce the pH of the cell and limit its growth. The aerobic system transfers energy more slowly, but has the greatest productivity, because carbohydrates or fats can be used as substrates for energy. All these systems can be used simultaneously in different cells of the body, and the cellular environment and energy requirements determine the preferred energy transfer system.
- The presence of oxygen and energy substrates
- two important factors of the cellular environment.
The type of muscle fibers and inherent characteristics are key factors in determining the energy transfer system for muscle cells. Dietary manipulation and training sessions can change the cellular environment and have a strong impact on the performance of the energy transmission system, as well as on energy substrates.