Adaptation in Sports Training

Atko Viru

• Publisher: Routledge
• Year: 2017
• ISBN:
  9781351469005
• Edition: 1
• Topic: Medicine
• Subtopic: Sports Medicine

Founded on an analysis of scientific literature and backed by an abundance of references, this timely new book examines problems related to sports training, as well as the concept that training-induced changes are founded on adaptive protein synthesis. Discussions include:

• Alterations in the organism's adaptivity during exercise training
  
• Intracellular control of protein synthesis points on molecular mechanisms in exercise training
  
• Endocrine mechanisms with regard to acute adaptation during exercise, as well as amplification and post-translation control of the adaptive protein synthesis
  
• Practical benefits of the adaptation process in training

Chapter 1

GENERAL OUTLINES OF ADAPTATION PROCESSES AND THE BIOLOGICAL NATURE OF EXERCISE TRAINING

ADAPTATION AND TRAINING

Muscular activity belongs to the group of factors closely related to adaptation processes in the organism. Every exercise triggers acute adaptation processes necessary to adjust body functions to the corresponding level of elevated energy metabolism. Adjustments are also necessary to avoid harmful alterations in the internal milieu of the organism. In turn, all these adjustments enable exercise performance and to a great extent determine the performance level. Systematic repetitions of exercises induce long-term stable adaptation that is founded on structural and metabolic changes, making possible increased functional capacities.

HOMEOSTATIC REGULATION

Since the publications of C. Bernard¹ and W.B. Cannon,^2,3 it is well recognized that adaptation to life conditions and to any kind of bodily activity is always directed towards maintaining or restoring the constancy of the body’s internal milieu. For this purpose certain specific reactions are introduced. The integrated sum of these reactions was defined by W.B. Cannon^2,3 as homeostatic regulation. However, only some of the parameters of the body’s internal milieu are kept at a constant level, while others vary to a great extent. Accordingly, the rigid and plastic constants of the internal environment were discriminated.⁴ The rigid constants have a very narrow range of fluctations between the resting and activity levels, deviations from which cannot be associated with maintenance of life. The plastic constants can change to a great extent. Often their changes are necessary to compensate for the influences on the rigid constants or to restore their activity (Figure 1-1). The changes of plastic constants may also reflect the mobilization of bodily resources for certain activities. However, there are also special mechanisms responsible for the limitation of alterations of plastic constants and for restoration of the resting levels.

The main rigid constants are temperature, pH, osmotic pressure, and contents of ions, water, and pO₂. It is simple to notice that there are conditions which determine the optimal activity of enzymes. This enables us to understand the importance of the constancy of rigid constants. Without the necessary conditions which ensure the optimal activity of enzymes, metabolic processes will be disturbed and possibilities of maintaining life will be reduced.

Homeostatic regulation is affected through controlling factors at the level of cellular autonomic, hormonal, and neural regulation. According to contemporary knowledge, the homeostatic function may be extended to many hormones and other bioactive substances in cooperation with processes triggered by direct nervous influences. In various cases, behavioral responses are included into homeostatic regulation as well.

FIGURE 1-1. Homeostatic regulation

MECHANISM OF GENERAL ADAPTATION

Adaptive processes cannot be limited by specific homeostatic reactions. In many cases nonspecific alterations, independent of the specific nature of the activity, are observable. The nonspecific character of adaptation is expressed by the theory of W.B. Cannon⁵ about the emergency function of the sympatho-adrenal system. L.A. Orbeli⁶ discussed the adaptive-trophic function of sympathic innervation. Originally, nonspecific adaptation processes were conceptualized by H. Selye.⁷ An extensive study of nonspecific adaptation responses enabled him to establish the stress reaction as a sum of nonspecific responses of the body to any strong demands made upon it.

The nonspecific adaptation responses constitute the mechanism of general adaptation^8,9 (Figure 1-2). The major components of the mechanism of general adpatation are: (1) mobilization of the body’s energy reserve, (2) mobilization of the protein resources, and (3) activation of the body’s defense faculties (immunoactivities etc.). As a result, increased possibilities will be provided on the one hand, for homeostatic regulation, and on the other hand, for actualization of any necessary bodily activities, including muscular exercises.

MOBILIZATION OF METABOLIC RESOURCES

The main principle of metabolic control is that the substrate/product ratio determines the activity of enzymes catalyzing respectively the conversing of a substrate (S) into a certain product (P) and the reaction in the opposite direction:

$\text{S}\frac{{\text{e}}_1\to }{\leftarrow {\text{e}}_2}\text{P}$

The increase of the substrate as well as the decrease of the product stimulate enzyme e₁ activity (catalyzes the conversion of the substrate S into the product P) and inhibit enzyme e₂ (catalyzes the opposite process) activity. The substrate can be converted into the product if the activity of enzyme e₁ surpasses the activity of enzyme e₂. The opposite situation will emerge in the decrease of the substrate and the increase of the product. Then an inhibition of enzyme e₁ and a stimulation of enzyme e₂ occurs. Due to that the reaction stops and is replaced by the opposite reaction.

FIGURE 1-2. A scheme of adaptation to stressor. In response to stressor both specific homeostatic mechanisms and the mechanism of general adaptation are activated. The latter consists in mobilization of energy reserve, protein resources, and defense faculties. The mobilization of the body’s energy reserve increases the possibilities for energy attaining of homeostatic responses. The mobilization of protein resources enables us to use an additional energy reserve as well as to induce rapid synthesis of enzyme proteins, which are necessary for actualizing the specific homeostatic mechanism, mobilization of energy reserve, and activation of immunologic responses and other defense faculties. Increased functional activity for actualizing the specific homeostatic reactions creates a specific induction of protein synthesis. After acute action of stressors it is expressed in adaptive synthesis of structure and enzyme proteins in conjunction with increased protein turnover. As a result the possibilities for concrete homeostatic response improve. This means the transition from short-term rapid adaptation to a stable continuous adaptation that is mainly pronounced in cases of repeated action of stressors.

Actually cellular autoregulation is more complicated. In most cases the regulation is actualized in the course of the whole metabolic pathway or metabolic cycle. In a number of cases the reaction is inhibited not by the immediate product, but by the product of some subsequent reactions. Moreover, besides the accumulation of the products, the inhibitory role also belongs to some other results of reactions (changes of intracellular pH, ionic composition, availability of coenzymes, etc.).

The onset of the intensification of glycogen degradation is determined by the activity of glycogen phosphorylase. The opposite process depends on the activity of glycogen synthase. Both enzymes exist in active and inactive forms. The actual enzyme activity depends on the ratio between active and inactive forms. The stimulation of enzyme activity consists of converting inactive forms into active ones. The inhibition is actualized by the conversion of active forms into inactive enzymes. As the main aim of glycogenolysis is the energy supply of ATP resynthesis, it is natural that the main stimulators of glycogen phosphorylase activity are the low level of ATP and high levels of ADP and AMP. Calcium and sodium ions as well as acetylcholine also increase the activity of glycogen phosphorylase. The liberation of acethylcholine and the increased levels of cytoplasmic calcium and sodium ions are the initial events of excitement of the cell, including excitement of the muscular cell that initiates the concentration. Hence, cellular activity itself rapidly adjusts energy production to meet the increasing needs. Nevertheless, the role of the substrate/product ratio is obvious: the intensity of the reaction catalyzed by glycogen phosphorylase decreases with the reduction of the intracellular glycogen store (substrate) and with the accumulation of glucose-6-phosphate (product of the next reaction). At the same time glucose-6-phosphate activates glycogen synthesis.

In further glycogenolysis an important stage is the conversion of fructose-6-phosphate into fructose-1,6-diphosphate. The reaction is catalyzed by phosphocfructokinase (PFK). Its activity is stimulated by the high level of fructose-6-phosphate (substrate), ADP and AMP, as well as by the low level of fructose-1,6-diphosphate (product). The reaction is inhibited by an increase in the ATP content.

If the intensity of glycogenolysis surpasses the intensity of oxidation processes, a part of pyruvate is converted into lactate. The latter inhibits a number of enzymes of gluconeogenesis (PFK etc.) as a product of th...