Endurance sports demand high aerobic capacity and fatigue resistance, while throws, jumps, and other activities of high intensity and short duration require maximum power regardless of fatigue. The composition of muscle fibers varies greatly among athletes of different specialities. This interaction justifies the myotypological changes associated with training, but perhaps it can also help explain the muscle deterioration associated with the ageing process.
#MUSCLE FIBER DESITY VS SKELETON ARMOR FREE#
Today the mechanisms of interaction between genetic programming and certain environmentally based factors, such as tissue hypoxia and oxidative stress (production of oxygen free radicals) are beginning to be known. It has been shown that the phenotypic expression of slow or fast fiber depends on several independent signalling pathways. That determines their physical capacity and fitness for different sports specialities. The genetic factors and the level of training cause wide individual variations in the fibrillar composition, even in the same muscles between different subjects. This is also reflected in a high heterogeneity in the topological distribution of the fibers in each muscle or muscle fascicle. Muscles vary their fibrillar composition to meet the functional demands from their role in movements or in maintaining the posture. 3 - Factors that affect heterogeneity in fibrillar composition Experimental demonstration in a mamifer muscle sectionįigure 4. This is confusing, since in humans it has been referred to as type IIb fibers that coincide in their characteristics with the IIc fibers of other mammals (see illustrations). Recent studies have shown that in humans only subtypes IIa and IIc exist. Mammalian rapid fibers have three main subtypes: IIa, IIb and IIc. They are present in the muscles involved in fast movements. They consume ATP at high speed through anaerobic mechanisms. Also sometimes referred to as 'white fibers', since they practically lack myoglobin and have low adjacent capillarization. Participate mostly in muscles of postural character. Participate in slow and reduced movements, generating little force. They practically do not tire or do it so slowly because they consume ATP at low speed. They are very resistant fibers to fatigue. Sometimes referred as 'red fibers', as they contain a large amount of myoglobin and have high capillary density in their contour. The classical nomenclature meets its histochemical qualities, which are associated with its protein composition and metabolic characteristics.īasically, two types of fibers are distinguished: Slow fibers or type I (slow-twitch): Depending on their speed of contraction, their resistance to fatigue and their metabolism, skeletal fibers are classified into different types. Not all the fibers that make up a particular muscle have the same mechanical and metabolic characteristics. 1 - Heterogeneity in the composition of muscle fibers