Dr.Biol., Professor Y.A. Bukov¹
PhD, Associate Professor L.M. Bukova¹
PhD, Associate Professor V.I. Malygina¹
V.M. Khodorchenko¹
P.S. Safronova^1
1V.I. Vernadsky Crimean Federal University, Simferopol

Keywords: gas mixtures, acute fatigue, rehabilitation, cyclists. 

Introduction. The major problem of the modern elite sport training is the use of various extra-training means contributing to the improvement of the athletes’ physical working capacity and competitive performance. Among the ways to complete these tasks should be the use of changed gas environment. Artificial gas mixtures of varying composition are applied in sports activities in three directions: as a method of diagnostics of the body's functional state, as an additional training tool, and as a rehabilitation tool. As of today, hypoxic training is the most reasonable and methodologically grounded training method, which is successfully used in various sports [2, 4]. There is also some evidence that short-term inhalations of hypercapnic gas mixtures are of diagnostic value [1]. In order to optimize the training process, it is suggested to use gas mixtures containing inert gases as a rehabilitation means [5-7]. In view of particular importance of the rehabilitation measures being carried out to intensify the training and competitive processes, it is extremely important to find the most effective means of rehabilitation, including using various gas mixtures which components can have a targeted effect on various mechanisms underlying the rehabilitation processes.

Objective of the study was to rate benefits of different gas mixtures applied for urgent rehabilitation in elite cycling sport after acute muscular fatigue.

Methods and structure of the study. 14 elite cyclists were sampled for the study. The state of acute fatigue was modeled by means of a step incremental cycle ergometer test. The initial load equaled 50W. The power was increased by 50W every 3 minutes of work until the onset of excessive fatigue. The cadence at each test stage was 60 rpm. The load power threshold was limited to 350W. The acid-base balance (ABB) was measured by means of equilibration using the OR-210/3 microanalyzer of the capillary blood. The following ABB parameters were registered: actual pH of the blood, excess non-volatile organic acids (BE), amount of buffer bases (BB), actual (AB) and standard (SB) bicarbonate concentration, partial pressure of CO₂ in the blood (PaCO₂), and total amount of dissolved and chemically bonded carbon dioxide (tCO₂). The respiratory functions were tested using the pneumotachometric and gasometric methods. The rehabilitation process efficiency was determined based on the ventilatory equivalent for oxygen (VEO₂) and respiratory coefficient (R). Artificial gas mixtures of varying composition were used as the rehabilitation means: 1.0%СО₂+35%О₂%; 35.5% О₂%;  20.2%О₂+Не (heliox). The exposure time shortly after the loading test equaled 10 minutes for each mixture. The tests were performed once a week, with one mixture being used in one test.

Results and discussion. Hyperventilation accompanied by the active release of carbonic acid is among the most important factors leading to the development of fatigue after intense muscular activity. The process of elimination of metabolic CO₂ is regulated by the intensity of hyperchloremic acidosis, which this process is in direct relationship to. Therefore, the main objectives at the urgent stage of rehabilitation are as follows: restoration of the acid-base balance, liquidation of the oxygen debt, development of the normocapnic state. This circumstance is of practical importance in those sports, where the specific character of sports activity is determined by the need to re-perform motor actions after a short break. This problem can be resolved through short-term inhalations of gas mixtures: hyperoxic, hypercapnic, and inert gases. The total amount of the work performed until the onset of acute fatigue averaged 19,600 kgm. At the same time, we detected some fundamental functional shifts, which were characterized by a decrease of the blood pH to 7.090±0.001, accumulation of a large amount of non-volatile organic acids, a decrease in the level of pCO₂ in the capillary blood to 32.2±0.69 mmHg. Due to the loss of a large amount of metabolic CO₂, there developed tissue hypocapnia that disturbed the alveolar gas exchange function. CO₂ retention and accumulation would, obviously, be the main mechanisms for increasing the oxygen utilization rate, accelerating the dissolution of non-volatile acids, and restoring the ABB parameters.

At the first stage, we used a hypercapnic-hyperoxic gas mixture containing 1.0%СО₂+35%О₂. Short-term breathing was accompanied by increased oxygen consumption, which values significantly exceeded the baseline ​​throughout the entire period of inhalation. Moreover, the respiratory coefficient decreased to 0.445±0.001, which indicated metabolic CO₂ retention. Small concentrations of CO₂ contributed to an increase in the degree of oxyhemoglobin in the blood and enhancement of the gas exchange function. Reduced CO₂ elimination contributed to the fastest restoration of ABB. The pCO₂ index reached the isocapnic level. At the same time, a lack of buffer bases was observed, which testified to the incomplete compensation for the metabolic shifts.

At the second stage, we applied a normobaric hyperoxic gas mixture containing 35.5%O₂. Inhalations of the hyperoxic gas mixture while increasing the alveolar-arterial pO₂ gradient made it possible to enhance oxygen diffusion through the aero-hematic barrier of pulmonary capillaries into the blood, which was reflected in the increased oxygen utilization rate. With the beginning of inhalations of O₂, its consumption increased significantly. There was registered a CO₂ buildup in the body, which was caused by a decrease in the pulmonary ventilation rate due to the elimination of the hypoxic factor during the chemoreceptor respiratory stimulation. However, we still observed some residual signs of metabolic acidosis after inhalations associated with under-recovery of the alkali reserve.

At the third stage, we analyzed the efficiency of using the oxygen-helium mixture (heliox) in the rehabilitation processes. Inclusion into the mixture composition of the lighter inert gas - helium instead of nitrogen contributed to the enhancement of the efficiency of the body’s energy-saving systems by minimizing the breathing resistance. The effects of heliox were accompanied by some kind of pulmonary ventilation reaction aimed at maintaining the optimal level of alveolar ventilation. Decreased reactivity of the respiratory center, depression of electrical activity of the respiratory muscles led to the restructuring of the dynamics of the respiratory system to a more favorable energy level. However, there was an increase in the relative oxygen utilization rate by more than 20.0%. The special physical properties of helium provided the necessary conditions for increasing the oxygen diffusion rate through the aero-hematic cell barrier. Obviously, the increased oxygen supply contributed to the manifestation of its various influences on the oxidation processes in tissues, which was reflected in the changed cellular metabolism [3]. In addition, the transition of respiration to a new functional level was accompanied by a rapid accumulation of metabolic carbon dioxide in the body. The respiratory coefficient at the end of the exposure reached its baseline values. Increased activity of the rehabilitation processes in the oxygen-helium environment contributed to a more rapid compensation for the metabolic acidosis. There was an increase in the buffer capacity of the blood relative its background values.

Therefore, in the state of acute muscle fatigue, breathing with the proposed gas mixtures contributed to the intensification of the processes of compensation for the metabolic shifts.

Conclusion. In the state of acute muscle fatigue, as opposed to usual atmospheric conditions, breathing with gas mixtures of varying composition was accompanied by the development of special states activating the processes of homeostatic regulation of the functional system that provides the body’s oxygen mode. The efficiency of the regulation was determined by the composition of the gas mixture, which must be taken into account when planning and conducting rehabilitation measures.

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Corresponding author: bukovya@rambler.ru

Abstract

In view of particular importance of rehabilitation measures being carried out in conditions of intensification of training and competitive processes, it is extremely important to find the most effective means of rehabilitation, including using various gas mixtures which components can have a targeted effect on various mechanisms underlying the rehabilitation processes.

Objective of the study was to estimate benefits of different gas mixtures applied for rehabilitation in elite cycling sport after acute physical fatigue. 14 elite cyclists sampled for the study were tested once a week by a new gas mixture each time. The study data were processed by the variation statistic tools using the Student t-criterion. A special priority in the study was given to the physical working capacity building mechanisms. Breathing with gas mixtures was found to facilitate the homeostatic control of the oxygen consumption regimen, with the control process varying with variations in the gas mixture. Findings of the study are recommended for application in rehabilitation system design.