HUMAN BIOCHEMISTRY - L. V. Kapilevich - 2016

PART 1. SPORTS BIOCHEMISTRY

MOLECULAR MECHANISMS OF FATIGUE, RECOVERY, AND ADAPTATION TO PHYSICAL EXERTION

In physiology, it is customary to distinguish between The concepts of physical fatigue (exercise-induced fatigue) and subjective tiredness. Fatigue is a state of the Organism resulting from work and objectively characterized by a decline in performance capacity; tiredness is the subjective aspect of fatigue, the mental experience associated with it, and the feeling of weariness.

Development of Protective (Transmarginal) Inhibition

Organismal fatigue during muscular work is primarily associated with the exhaustion of the Central Nervous system, since intense muscular activity is simultaneously an intense activity of the nerve centers. The latter becomes impaired As a result of prolonged, strenuous work. The expression of this impairment is an alteration in the normal balance between Excitation and Inhibition processes, with the inhibitory process beginning to prevail. As a result, the normal course of reflex processes is disrupted, The regulation of autonomic Functions and coordination of movements are impaired, and the motor apparatus gradually enters an inactive state.

The Nervous System is the most sensitive to Changes in the internal environment. Such fatigue factors as the accumulation of Metabolic waste products in the Blood, a decrease in blood sugar levels, and, under certain conditions, oxygen deficiency in the blood, lower the organism's performance capacity not directly, but mainly indirectly—through the central nervous system.

Work associated with overcoming ultra-long distances in various sports is performed over an extended period, during which the nerve centers gradually fatigue. The intensive activity of the cardiovascular and respiratory systems over a long term leads to a decline in the Functional Properties of their neural regulatory apparatuses. Thus, the decrease in performance capacity during prolonged exertion, caused by the functional disruption of corresponding nerve centers, is also linked to the gradual alteration of circulatory and Respiration functions.

An important factor of fatigue during strenuous work of moderate power (such as ultra-long-distance running and swimming, cross-country skiing, etc.) should be considered the decrease in blood sugar concentration—hypoglycemia. A reduction in blood sugar levels serves as a signal of an impending substantial change in the organism's internal environment and, at the same time, as a trigger for compensatory reactions aimed at mobilizing CARBOHYDRATES from storage depots and converting fats and Proteins into carbohydrates, and subsequently, as a cause of such changes in central nervous system activity that may lead to the complete cessation of work. The intake of carbohydrates (50–100 g of sugar) during prolonged work has a positive effect on the functional state of the central nervous system, thereby enhancing the organism's performance capacity, reducing fatigue, or delaying its acute onset.

In addition to lowered blood sugar concentration, impaired thermoregulation may play a role in The Development of fatigue during prolonged strenuous work. Sweating, if it is not accompanied by the evaporation of sweat from The surface of the body or clothing, does not lead to an increase in heat dissipation. When heat dissipation lags behind the level of heat production during muscular work, it results in an elevated body Temperature, which can negatively affect performance capacity (if the temperature rise is significant). This is particularly likely to occur in environments with high humidity and low clothing permeability.

Strenuous activity of the nerve centers during high-power muscular work leads to their depletion faster than during moderate-power work. Furthermore, the performance capacity of the respiratory and circulatory Organs declines more rapidly than in moderate-power work.

High-power work is performed under conditions of a false steady state. Oxygen consumption reaches its maximum capacity (up to 4.5–5 liters in well-trained individuals), while simultaneously lagging significantly behind the oxygen demand. Consequently, the work is performed under conditions of oxygen deficiency, and the oxygen debt steadily increases during the exercise. The consequence of this is the accumulation of under-oxidized metabolic products in the organism. Thus, significant factors of fatigue during high-power work are the growing Oxygen debt and the associated accumulation of under-oxidized products, which leads to the suppression of nerve center activity.

Fatigue during maximal and submaximal power work is primarily associated with changes in the functional state of the central nervous system. High-frequency and high-force Muscle contractions are triggered by the intensive activity of nerve centers. At the same time, the central nervous system is subjected to a powerful influx of centripetal proprioceptive impulses originating from the periphery of the motor apparatus. As a result, a state of parabioitic inhibition develops within the nerve centers, and their functional mobility decreases, which precludes the generation of centrifugal impulses at the initial rhythm; consequently, the Movements of the runner, swimmer, etc., slow down and become constrained.

Mechanisms of Recovery After Muscular Work

As early as I. P. Pavlov, A number of regular patterns governing recovery processes were discovered, which have not lost their significance today.

1. In a working organ, alongside processes of degradation and depletion, a recovery process takes place; it is observed not only after the completion of work, but already during the activity itself.

2. The relationship between depletion and recovery is determined by the intensity of the work; during intense work, the recovery process is unable to fully compensate for the expenditure, and therefore full restitution of losses occurs later, during rest.

3. The restoration of expended resources does not stop at the baseline level, but proceeds with a certain overshooting (The phenomenon of supercompensation).

I. P. Pavlov’s views were further developed by his student Yu. V. Folbort (1951), who concluded that repeated physical exertion can lead to two opposite states: if each subsequent bout of exertion falls within the recovery phase in which the organism has reached its baseline state, a state of training is developed and the functional capabilities of the organism increase; however, if performance capacity has not yet returned to baseline, a new bout of exertion triggers the opposite process—chronic exhaustion. The gradual disappearance of fatigue symptoms, the return of the organism's functional status and performance capacity to pre-work levels, or exceeding the latter, corresponds to the recovery period. The duration of this period depends on The Nature and degree of fatigue, the state of the organism, the characteristics of its nervous system, and environmental conditions. Depending on the combination of these factors, recovery takes varying amounts of time: from minutes to several hours or even days in cases of the most strenuous and prolonged work.

Depending on the general direction of BIOCHEMICAL SHIFTS IN the organism and the time required for them to return to normal, Two Types of recovery processes are distinguished: urgent and delayed. Urgent recovery covers the first 0.5–1.5 hours of rest following work; it boils down to eliminating anaerobic breakdown products accumulated during exercise and replenishing the incurred oxygen debt. Delayed recovery spans many hours of rest after work. It consists of enhanced plastic METABOLISM processes and the restoration of ionic and endocrine balance disrupted during exercise. During the delayed recovery period, the return of the organism's energy reserves to normal is completed, and the synthesis of structural and enzymatic proteins broken down during work is intensified. To ensure the rational alternation of loads, it is necessary to account for the rate at which recovery processes proceed in athletes' bodies following individual exercises, exercise complexes, training sessions, and microcycles.

A distinguishing feature of recovery processes following training and competitive loads is the non-simultaneous (heterochronic) return of various indicators to their baseline levels after the completed training load.

Glycogen synthesis occurs in the Muscles and Liver from glucose supplied to the organism via food. The maximum time required for the restoration of glycogen reserves in the organism is 24–36 hours.

Fat synthesis takes place in adipose tissue from dietary fats. Replenishing fat reserves takes no more than 36–48 hours.

Protein Synthesis occurs mainly in Muscle tissue. A portion of Amino Acids (Essential Amino Acids) must necessarily be supplied with food. The maximum time for Protein synthesis is 48–72 hours.

Delayed recovery also includes the restoration (repair) of damaged intracellular structures. This applies to myofibrils, Cell/35.html">Mitochondria, and various cell membranes. In terms of time, this is the longest process, requiring up to 72–96 hours.

Methods for Accelerating Recovery

In Structure/182.html">Practical Application, recovery means are most commonly divided into three main groups, the integrated use of which constitutes the recovery system: pedagogical, biomedical, and psychological.

Pedagogical means can be considered the most effective because, regardless of how potent the biomedical and psychological interventions might be, they can only be viewed as auxiliary. They facilitate accelerated recovery and enhanced athletic performance only when training is rationally structured. To achieve a training effect commensurate with the body's physiological capabilities, it is necessary to ensure:

✵ rational training planning, i.e., matching workloads to the functional capacities of the body;

✵ a rational combination of General and Specific means;

✵ optimal Structuring of training and competitive micro-, macro-, and mesocycles;

✵ extensive use of activity switching for the athlete;

✵ the Introduction of recovery microcycles;

✵ The Use of training in mid-altitude and high-altitude conditions;

✵ a rational general lifestyle schedule;

✵ proper structuring of individual training sessions, creating a positive emotional tone for training;

✵ individually tailored warm-ups and cool-downs;

✵ the use of active rest and relaxation.

In sports training, alongside pedagogical methods, biomedical recovery means are widely employed. These include: balanced Nutrition, physical and hydrotherapy Procedures; various types of massage; intake of protein supplements and sports drinks; balneotherapy, local negative pressure (LNP, barotherapy), saunas, Oxygen therapy, oxygen cocktails, adaptogens, and agents affecting Energy Metabolism, as well as electrical stimulation and air ionization, among others. The action of these means is aimed at replenishing the energy and plastic resources expended during exercise, restoring vitamin balance, micronutrients, thermoregulation, and blood supply, and enhancing enzymatic and immune activity. Consequently, this not only facilitates the natural course of recovery processes but also boosts the body's defense mechanisms and its resistance to various adverse and stress factors. In addition to all the above, specialists classify balanced nutrition, pharmacological agents (excluding banned substances), and Vitamins as biomedical recovery means. Adhering to a hygienic daily routine and the consistent alternation of its components (Sleep, nutrition, work, and athletic activities) is of great importance.

To manage mental state and alleviate the neuro-emotional stress of athletes, specialists recommend the following techniques: suggestion, sleep-rest, autogenic training, psychoregulatory training, activating therapy, muscle relaxation techniques, specialized breathing exercises, comfortable living conditions with distractive factors and the exclusion of negative emotions, as well as diverse leisure activities tailored to the athlete's individual inclinations, particularly when forming teams during the pre-competition period.

Biochemical Patterns of Adaptation to Muscular Work

Adaptation of the body to constantly changing environmental conditions (external and internal) is a continuous process of adjustment aimed at maintaining homeostatic balance. This section examines the adaptation of an athlete's body to muscular work, as biochemical mechanisms make a significant contribution to its manifestation.

The generally accepted definition of such adaptation is as follows. Adaptation to muscular work is the Structural and functional restructuring of the body that enables an athlete to perform physical loads of greater power and duration, and to develop higher muscular forces compared to an untrained individual.

Urgent (Acute) Adaptation

Urgent adaptation is the body's response to a single bout of training load, manifested as an "emergency" adjustment to the altered state of the internal environment. This response primarily reduces to changes in energy metabolism and the activation of higher neural centers responsible for the REGULATION OF ENERGY metabolism.

The main alterations in catabolic processes that lead to enhanced energy supply for physical exertion include the following:

✵ acceleration of liver glycogen breakdown with The formation of free glucose (stimulated by adrenaline);

✵ enhancement of aerobic and anaerobic oxidation of muscle glycogen, ensuring The production of large amounts of ATP under The Influence of adrenaline;

✵ an increase in The rate of tissue respiration in mitochondria. This occurs for two reasons: first, the supply of oxygen to the mitochondria increases; second, The activity of tissue respiration Enzymes rises;

✵ increased mobilization of fat from adipose depots under the Influence of the sympathetic nervous system and adrenaline;

✵ increased rate of Fatty acid oxidation and ketone body formation;

✵ suppression of anabolic processes, primarily affecting PROTEIN SYNTHESIS AND triggered by glucocorticoids.

Long-term (chronic) adaptation

As for long-term adaptation, it develops gradually through the repeated Implementation of acute adaptation via the summation of the aftereffects of recurring loads.

The Morphology/3.html">MAIN DIRECTIONS OF long-term adaptation can be outlined as follows:

✵ enhanced rate of recovery processes, particularly accelerated synthesis of proteins and Nucleic Acids;

✵ increased content of intracellular Organelles—myofibrils, mitochondria, and the sarcoplasmic reticulum; ultimately, these changes lead to muscle hypertrophy;

✵ improved mechanisms of neurohormonal regulation, accompanied by an increased synthetic capacity of Endocrine glands, which allows for maintaining high blood levels of Hormones essential for muscular activity over longer periods during exercise;

✵ development of resistance to biochemical shifts. This includes the body's tolerance to increased acidity caused by lactate accumulation. It is hypothesized that the desensitization to rising acidity in adapted athletes is due to the formation of molecular forms of proteins that retain their biological functions at lower pH levels.

Acute and long-term adaptation exert a mutual influence on each other. Acute adaptation triggers profound biochemical and functional shifts in the body, which in turn activate the mechanisms of long-term adaptation. Conversely, long-term adaptation expands the capacity for acute adaptation. This interplay between acute and long-term adaptation progressively leads to an increase in an athlete's physical performance.

Training effect

In sports practice, Three types of training effects are used to assess The impact of the training process on the formation of adaptation to muscular work: acute, delayed, and cumulative.

The acute training effect characterizes acute adaptation. Essentially, the acute training effect represents the biochemical shifts in the athlete's body caused by the processes that constitute acute adaptation. These shifts are recorded during Physical Exercise and throughout the acute recovery phase.

The delayed training effect refers to the biochemical changes that occur in the athlete's body in the days following a workout, i.e., during the period of delayed recovery. The primary manifestation of the delayed training effect is the supercompensation of substrates utilized during physical work. These primarily include Muscle Proteins, creatine phosphate, as well as muscle and liver glycogen.

The cumulative training effect reflects the biochemical shifts that gradually accumulate in the athlete's body during prolonged training. In particular, the increase in the indicators of acute and delayed effects over the course of extended training can be attributed to the cumulative effect.

The cumulative effect is specific in nature, and its manifestation largely depends on the character of the training loads.

Self-Assessment Questions

1. From a biological perspective, what causes fatigue?

2. What are the consequences of protective inhibition developing in the Brain?

3. What is the difference between local and general fatigue?

4. Through what mechanisms can fatigue be reduced?

5. Name the causes responsible for the onset of protective inhibition.

6. What processes take place in the body during the acute recovery period?

7. What biochemical processes play a major role during delayed recovery?

8. Over what timeframe are protein reserves replenished in the body?

9. What is The Essence of the supercompensation phenomenon?

10. What factors determine the magnitude of supercompensation?

11. What biomedical methods are used to accelerate recovery processes?

12. What psychological methods are used to accelerate recovery processes?

13. Are there any permitted pharmacological agents that accelerate body recovery?

14. How are energy resources maintained in The Human Body during prolonged physical exertion?

15. What are the two types of adaptation distinguished in science?

16. When do immediate adaptation processes take place?

17. How is the adaptation process regulated?

18. What processes occur during the stage of immediate adaptation?

19. What processes occur during the stage of long-term adaptation?

20. What is The ultimate outcome of chronic adaptation?

21. What types of training effects are distinguished?