Biochemical Foundations of Human Vital Activity - Volkov N.I., Nesen E.N. 2000

Biochemistry of Sports
Biochemical Control in Sports
Biochemical Control of the Development of the Body's Energy Supply Systems During Muscular Activity

Athletic performance is, to a certain extent, limited by the development level of the body's energy supply mechanisms. Therefore, sports practice involves monitoring the power, capacity, and efficiency of anaerobic and aerobic energy production mechanisms during training, which can also be assessed through biochemical indicators.

To evaluate the power and capacity of the phosphocreatine energy production mechanism, researchers use indicators such as total alactic oxygen debt, creatine phosphate levels, and Muscle creatine kinase activity. These indicators are significantly higher in trained individuals, pointing to an enhanced capacity of the phosphocreatine (alactic) energy pathway (Table 52).

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Fig. 218. Increase in Blood inorganic phosphate in low-skilled (1) and highly skilled (2) rowers following anaerobic physical exertion

The degree to which the phosphocreatine mechanism is engaged during physical exertion can also be estimated by the elevated blood concentrations of PCr metabolic breakdown products (such as creatine, creatinine, and inorganic phosphate) or changes in their urinary excretion.

To characterize the glycolytic energy production mechanism, experts frequently measure the peak accumulation of lactate in arterial blood during maximal physical exertion, as well as total and lactate oxygen debt, blood pH, acid-base balance (ABB) parameters, blood glucose and muscle Glycogen levels, and The activity of Enzymes such as Lactate dehydrogenase and phosphorylase.

An improvement in athletes' glycolytic (lactic) energy capabilities is indicated by a delayed time to peak blood lactate during maximal exertion, alongside higher overall lactate levels (see Table 52). In elite speed-event athletes, blood lactate during intense exercise can rise to 26 mmol ⋅ л^-1 or more, whereas in untrained individuals, the maximum tolerable blood lactate is 5—6 mmol л^-1, with 10 mmol ⋅ л^-1 potentially being fatal against a normal resting range of 1—1,5 mmol л^-1. This expansion of glycolytic capacity is accompanied by increased glycogen stores in skeletal Muscles—particularly in fast-twitch fibers—and elevated glycolytic enzyme activity.

To assess the power of the aerobic energy mechanism, the most common metrics include maximal oxygen uptake (VO_2mах), the onset of blood lactate accumulation (OBLA / AT), and the concentration of blood Hemoglobin as an indicator of the Oxygen transport system. An increased VO_2mах reflects higher aerobic energy output. In untrained adults, absolute VO_2max typically averages 3.5 L ⋅ min^-1 for men and 2.0 L ⋅ min^-1 for women, depending on body mass. In elite endurance athletes, absolute VO_2max values can reach 6—7 L ⋅ min^-1 in men and 4—5 L ⋅ min^-1 in women.

TABLE 52. Changes in indicators of anaerobic energy production mechanisms during training

The duration of work performed at the AT (anaerobic threshold) level serves as an indicator of enhanced energy capacity. Untrained individuals cannot sustain physical work at the AT level for longer than 5—6 minutes, whereas endurance-trained athletes can maintain it for 1—2 hours.

The efficiency of the aerobic energy mechanism depends on The rate of mitochondrial oxygen utilization, which is primarily determined by the activity and quantity of Oxidative Phosphorylation enzymes, mitochondrial density, and the proportion of fats utilized for energy production. Intensive endurance-oriented training enhances aerobic efficiency by increasing the rate of fat oxidation and elevating their contribution to the energy supply during exercise (Fig. 219).