In general terms, the biochemical parameters of exercise can be summarized in a discrete number of definitions, as follows:

• Maximum oxygen consumption (VO2max): This defines the maximum sustainable exercise intensity by aerobic mechanisms of energy production, i.e., the maximum amount of oxygen usable in a unit of time per body weight (ml/kg/min). Used as a synonym for maximum aerobic power, it substantially depends on the availability of oxy gen guaranteed by the integration of respiratory function (respiratory volume, lung ventilation, gas diffusion rate), cardiovascular function (heart rate, systolic volume, blood flow velocity), and blood transport capacity (amount of hemoglobin and hemoglobin saturation). The value of VO2max can be plastically modified by training, usually increased up to 25%, but tends to physiologically decrease gradually with increasing age.

 • Anaerobic threshold: This defines the maximum intensity of a physical exercise at which the ratio between generation and elimination of lactic acid in the blood remains constant (i.e., lactacidemia). It also expresses the intensity of work at which a blood concentration of lactic acid equal to 2–4 mmol/L is reached (i.e., in sedentary subjects or devoted to modest physical activity). It is therefore identified by the intensity of physical effort beyond which the metabolism remains aerobic in prevalence. Beyond this threshold, lactic acid begins to accumulate, and it is associated with fatigue and muscle pain. The volume of oxygen needed to bring the muscular system into aerobic conditions is therefore defined as an “oxygen debt.”

• Aerobic capacity: Although there is no agreed-upon definition, as with anaerobic capacity, this term generally refers to the maximum amount of oxygen per minute required to perform muscular work. It depends on respiratory, cardiovascular, and blood functions as well as on the ability of the tissues to use oxygen.

• Anaerobic capacity: This essentially expresses the oppo site of the previous definition and, therefore, the ability to perform muscular work under conditions of oxygen absence. It, therefore, depends to a large extent on the availability of the substrates of alactacidic and lactacidic anaerobic metabolism. In practice, it is defined as the ability to continue performing muscular work by simultaneously accumulating lactic acid. Some authors identify anaerobic capacity with the lactate concentration measured after a maximal middle-distance run (usually 800 m, with an average lactic acid concentration of 12.5 mmol/L).

The thresholds that distinguish the different areas can vary widely in the population, both as a result of genetic characteristics and following adaptations induced by training. For example, it is evident that a subject with a “congenital” high pulmonary capacity (e.g., >6 liters), a “naturally” low resting heart rate (e.g., 40 beats per minute), and “physiologically” high values of hemoglobin (e.g., >170 g/L) will have an extremely high VO2max (e.g., >90 mL/min/kg), will be able to express a higher anaerobic threshold, and will have greater aerobic power. This will almost certainly translate into an increased ability to excel, especially in endurance sports. It is also not difficult to understand how all the parameters that express athletic capacity differ substantially between a hypothetical sedentary subject and a “champion” of endurance sports (resting heart rate: 60–80 vs. 35–55 beats per minute; threshold frequency: 150–170 vs. 170–190 beats per minute; lung capacity: 3–4 vs. 6–7 liters; VO2max: 30–50 vs. 90–100 mL/min/kg; maximum aerobic power: 2–4 vs. 5–8 mL/min).

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مواضيع ذات صلة

Clinical Biochemistry of Metabolic Substrates

Generalities on the Structure and Biochemistry of the Skeletal Muscle

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

Cardiac Muscle Resembles Skeletal Muscle in Many Respects

Contraction is Orchestrated by the Second Messenger Ca2+

Muscle Converts Chemical Energy to Mechanical Energy

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