For a better understanding of the clinical biochemistry of exercise, it is worth remembering that muscle fibers are not all the same but are divided into three types:

• Slow fibers (type I; also known as “slow-twitch fibers”) are red, thin, resistant, and highly vascularized with pre dominantly aerobic metabolism.

• Fast fibers type A (type IIa; also known as “fast-twitch fibers – A”) are white, coarse, and characterized by rapid/ resistant contractions and glycolytic oxidative metabolism.

• Fast fibers type B (type IIb; also known as “fast-twitch fibers – B”) are white, large, and characterized by explosive contractions and anaerobic metabolism.

The speed of contractions of the different types of fibers is different. Given a maximum value of 100%, the speed of white fibers of type IIB is just 100%, decreasing to ~50% for white fibers of type IIA and down to ~10% for red fibers of type I. The different fiber composition is partly defined by genetic inheritance and partly modifiable by exercise. It is therefore evident that marathon runners, road cyclists, and cross-country skiers are generally characterized by a high percentage of slow fibers (between 60% and 80%), whereas this percentage decreases substantially in sprinters (e.g., 100 meters) to 30–40%. Without entering into dangerous ethical considerations, the genetic and/or biochemical analysis of muscle fibers would (at least theoretically) allow us to predict the most appropriate sport for each subject. Nevertheless, as is well-known, the ability to excel in a sport is not only defined by the physical constitution of the athlete but also mainly depends on training, technique, and psychology (e.g., the ability to resist fatigue, the “will to win”).

Regardless of muscle tissue composition, muscular work has a number of essential characteristics that explain how it works. They can be summarized as follows:

• Muscle strength, which represents the ability to develop tension and overcome an external resistance or oppose it. It is substantially dependent on mass, fiber composition, and speed of contraction.

• Muscle speed, which indicates the ability to contract in the shortest possible time. It is substantially dependent on fiber composition, enzymatic equipment, tension, and motor activation pattern.

• Muscular endurance, which indicates the ability to maintain a certain tension over time. It is substantially dependent on fiber composition, enzymatic equipment, and muscular circulation.

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مواضيع ذات صلة

Iron is Strictly Conserved

Haptoglobin Protects the Kidneys

The Levels of Certain Plasma Proteins Increase During Inflammation or Following Tissue Damage

Albumin is the Most Abundant Protein in Human Plasma

Biochemical Parameters for Assessing Athletic Performance

Clinical Biochemistry of Metabolic Substrates

Plasma Contains A Complex Mixture of Proteins

Intermediate Filaments Differ From Microfilaments & Microtubules

Microtubules Contain α- & β-Tubulins

Muscle Tissue are The Target of Several Genetic Disorders

Skeletal Muscle Contains Slow (Red) & Fast (White) Twitch Fibers

Muscle Contraction Requires Large Quantities of ATP