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

Biochemistry of Sports
Biochemical Factors of Fatigue
Biochemical factors of fatigue during short-term exercises of maximal and submaximal power

It has been established that the shorter the duration of an exercise and the higher its intensity, the greater the role played in The Development of fatigue by factors associated with the specific Nature of the muscular work performed. During short-term exercises of maximal and submaximal power, the initial signs of fatigue are primarily linked to the bioenergetic processes in working Muscles aimed at maintaining a high rate of ATP resynthesis. Changes in mechanical performance indicators during these types of exercise typically appear when the PCr reserves in the working muscles are depleted by more than half of their initial values, and intracellular pH drops significantly due to a sharply accelerated Glycolysis. Fig. 148 illustrates the moment when, as the PCr concentration falls below this critical threshold, There is a sharp increase in The rate of ADP formation and H⁺ accumulation. The concentrations of key metabolites reflecting changes in anaerobic METABOLISM/26.html">Energy Metabolism in the fatigued state are presented in Table 30.

The data show that changes in ATP concentration during fatigue development in short-term high-intensity exercise are relatively small. The greatest changes and the strongest correlation with fatigue-induced shifts in force and power indicators are exhibited by the concentrations of ADP, H⁺, and lactate. As is known, Changes in the concentrations of the aforementioned metabolites exert a pronounced inhibitory effect on Myosin ATPase—the key enzyme responsible for the efficient Conversion of the energy of ATP high-energy phosphate bonds into mechanical Muscle work. From this perspective, The formation of ADP and the accumulation of H⁺ during muscular contractile activity should be regarded as the primary factors responsible for the onset of fatigue during short-term high-intensity exercise.

Class="center">TABLE 30 Concentration of Major Energy Metabolism Metabolites in Working Muscles

Note. The given concentration values refer to molecules located in the cytosolic solution. Since the Water concentration in the Cytosol is approximately 78% of the wet muscle mass, the actual concentration values should be multiplied by 1.3 of the ATP phosphate bonds into mechanical muscle work. From this perspective, the formation of ADP and the accumulation of H⁺ during muscular contractile activity should be regarded as the primary factors responsible for the onset of fatigue during short-term high-intensity exercise.

Fig. 148 Changes in the concentration of ATP, ADP, PCr, and hydrogen ions in working muscles during short-term high-intensity exercise

Fig. 149 Glycogen concentration in muscle fibers during short-term high-intensity (a) and prolonged moderate (b) exercise

In addition to the factors mentioned above, fatigue development during short-term maximal and submaximal power exercises is significantly influenced by the depletion of intramuscular glycogen reserves (Fig. 149, a). In the fatigued state following short-term high-intensity exercise, a marked decrease in glycogen reserves is observed in fast-twitch fibers, whereas following prolonged moderate work, the greatest shifts in glycogen content occur in slow-twitch fibers (Fig. 149, b). Furthermore, The production of lactic acid via glycolytic glycogen breakdown during short-term high-intensity exercise correlates with the fatigue-induced decline in work output (Fig. 150).

At a high frequency of muscle stimulation during short-term high-intensity exercise, a noticeable contribution to fatigue development is made by impairments in excitation-contraction coupling during neuromuscular transmission, changes in CNS activity due to protective inhibition, disruptions in neural trophic support and cerebral Blood flow, changes in inorganic phosphate and inosine monophosphate concentrations, and the accumulation of ammonia in Tissues. Fig. 151 schematically illustrates the complex, multifactorial nature of fatigue developing during maximal and submaximal power exercises.

Fig. 150 Relationship between lactate accumulation in working muscles and the decrease in exercise intensity due to fatigue

Fig. 151 Contribution of various factors to the development of fatigue during short-term high-intensity exercise