Dr.Hab., Professor Yu.S. Vanyushin
Ph.D., Associate Professor R.R. Khayrullin
Kazan State Agrarian University, Kazan

Keywords: cardiorespiratory system, chronotropic and inotropic types of adaptation, athletes, step exercise.

Introduction. Modern information technologies make it possible to conduct a comprehensive analysis of the functional state of the body, i.e. there is a possibility of a multiparameter analysis of the studied function at the system level. This idea is at the basis of the theory of functional systems [1, 4]. In biology and medicine a system approach has been used starting with the works of Ludwig von Bertalanffy (1973), a Canadian biologist. The approach is based on the definition of a system as a unity of the multitude of its constituent elements. Therefore, studying an organism as a whole should be approached comprehensively, which implies an instantaneous comparison of many functional parameters [5]. In connection with this expediency of simultaneous registration of components of a functional system is obvious for drawing up models of vegetative support of muscular activity [6].

Cardiorespiratory system is one of the most important functional systems. Oxygen supply to the body as well as sports performance and health of athletes largely depend on their activity. Functional state of the body of an athlete can be assessed by its performance as it serves as an indicator of functional and reserve capacities. It is especially important for those involved in endurance sports [2, 3].

The purpose of the research was to determine the functional state of athletes from different sports and age groups based on a range of inter-related physiological responses of the cardiorespiratory system under step load.

Materials and methods. In biomedical research physical loads that have a high diagnostic value and can be used as means of simulating various human activities became widespread. Cycle ergometry is considered to be a generally accepted and preferred one, thus making it easier to obtain physiological data during motor activity and the possibility of precise physical load dosage both in terms of the power and in terms of the duration of the work performed [2-6]. Step load on a cycle ergometer from 50 to 200 watts without rest was applied in the study. Each level of load lasted 4 min. The following parameters of the cardiorespiratory system were recorded: HR (heart rate), SV (stroke volume), CO (cardiac output) that were determined by the method of W.G. Kubicek et al. (1966), RMV (respiratory minute volume) determined using a pneumotachograph, SVI (stroke volume index), CI (cardiac index) and OUC (oxygen utilization coefficient) that were calculated. The coefficient of comprehensive assessment of the cardiorespiratory system [2, 3] was used to estimate compensatory and adaptive reactions of athletes. 73 males aged 17 to 35 years were involved in the studies. They were divided into groups based on age periodization and specific sports. The first group (22 persons) consisted of young men (17-21 years old) engaged in cyclic sports, the second group (17 persons) – young men (17-21 years old) engaged in acyclic sports, the third group (20 persons) – adult athletes (22-35 years old) engaged in cyclic sports, and the fourth group (14 persons) – adult athletes (22-35 years old) engaged in acyclic sports.

Results and discussion. Heart performance parameters in the groups of athletes increase along with the increase of the load (Table 1).

Table 1. Heart performance parameters (HR, SV, CO) of athletes from different sports and age groups under step load

Note: * - statistical significance of differences between the groups of adult athletes engaged in cyclic and acyclic sports;

+ - statistical significance of differences between the groups of young and adult athletes engaged in cyclic sports.

However, at the same time some characteristics are noted associated with both the age of the athletes and the sport. Groups of athletes of different age involved in different kinds of sports respond to physical load differently and have different ranges of adaptive capability of physiological functions. For example, in the groups of athletes engaged in acyclic sports age did not influence the heart performance parameters (HR, SV and CO) under step load. As the load increased, all these parameters changed unidirectionally and without significant differences between the groups of young and adult athletes. This can be explained by the fact that athletes in these groups were practicing the same sport and mechanisms of urgent adaptation under load apparently do not depend on age characteristics of the test subjects.

In the groups of athletes engaged in cyclic sports age had an impact on the heart performance parameters. Starting with the load of 150 watts HR was higher in the groups of young athletes, and SV was higher in the groups of adult athletes. It is probable that in the groups of athletes engaged in cyclic sports age affects the dominant mechanism (chronotropic or inotropic) involved in maintaining cardiac output.

Some authors [2, 3] called the phenomenon when SV stops growing a threshold of adequate hemodynamic response. As follows from the results of our research, the threshold of adequate hemodynamic response is affected by the type of sports activity. The increase of cardiac output during motor activity took place due to the growth of the heart rate or the SV value, and in some cases due to the growth of both heart performance parameters. However, their contribution into the growth of CO is not equal. For example, stroke volume can increase by not more than 2 times with regards to the baseline values, whereas HR can increase 3 times and more under maximum load. At the same time the lower HR at rest, the higher the chronotropic characteristics of the heart. It is believed that maximum values of the chronotropic heart response are biologically determined by the functional features of the sinoatrial node. Therefore an increase of SV, the value of which depends on the basal blood reserve volume, is the main factor of CO optimization in athletes, particularly in endurance sports. However, in undertrained people SV increase takes place due to the chronotropic response of the heart. We observed it in the groups of young and adult athletes involved in acyclic sports. In this case, the threshold of adequate hemodynamic response was 50 watts.

The threshold was set at the load of 100 watts in the groups of young and adult athletes involved in cyclic sports. The mechanism of considerable SV increase under step load in these groups can probably be explained by the fact that their left ventricular diastolic and systolic volumes are larger than those of athletes from the other groups [2, 3]. It is probable that during physical exercise these volumes reduce more, thus determining a significant increase of SV.

The load of 150 and 200 watts on the cycle ergometer led to a further increase of heart rate in all the groups. CO increase was mainly due to the chronotropic effect when it is the quickening of the heart that indicates the tolerance of the applied load.

The most complete understanding of the adaptation of the body to the load can be obtained by a simultaneous comparison of many functional parameters of the cardiorespiratory system [2-6]. CO is one of the most important indicators as oxygen supply to the body during muscle activity largely depends on it. However, the results we have obtained (Table 2) show a decrease in CO increase during the transition from one load to another. We can therefore assume that there exist other mechanisms aimed at meeting the oxygen demand of the body during the muscle activity. One of them is external respiration that, according to some researchers [2, 3], can be considered a factor limiting the possibility of achieving top performance in sport.

Table 2. Cardiorespiratory system parameters of athletes from different sports and age groups under step load

Note: * - statistical significance of differences between the groups of adult athletes engaged in cyclic and acyclic sports;

- - statistical significance of differences between the groups of young and adult athletes engaged in cyclic sports;

+ - statistical significance of differences between the groups of young athletes engaged in cyclic and acyclic sports.

The highest values of pulmonary ventilation (RMV) were recorded in the groups of athletes involved in acyclic sports, regardless of age, under the load of 200 watts (Table 2). In this case external respiration in the groups of athletes involved in acyclic sports can be considered as one of the compensatory mechanisms aimed at meeting the oxygen demand of the athletes while increasing the cycloergometric load with relatively lower values of cardiac output. It should be noted that the result of pulmonary ventilation obtained is not a criterion of a considerably high level of fitness as it increases the oxygen and energy cost of breathing. Under these conditions the adaptation to muscular activity is best accomplished by activating and enhancing the efficiency of the oxygen transport system. This is evidenced by the significantly higher values of the stroke volume index and cardiac index in the group of young athletes aged 17-21 engaged in cyclic sports.

In the course of adaptation of the body to muscular activity complex relationships even within one and the same functional system occur. This can be seen through the example of the interaction of the cardiovascular and respiratory systems that provide athletes with oxygen when under step load. To assess the compensatory and adaptive responses of the bodies of athletes from different sports and age groups while under step load we used the coefficient of the comprehensive assessment of the cardiorespiratory system [3], which showed the presence of high functional capacities in the groups of athletes involved in cyclic sports at the age of 17-21 and 22-35 years under the load of 150 watts, as well as the replacement of functions in the bodies of athletes involved in acyclic sports. A significant decrease in the coefficient of the comprehensive assessment of oxygen supply to the body in the groups of athletes involved in acyclic sports under the load of 150-200 watts reflects a high “physiological cost” ensuring the delivery of oxygen to the working skeletal muscles.

Conclusion. Athletes involved in cyclic sports showed the dominant mechanism of adaptation (chronotropic or inotropic) starting with load power of 150 watts, depending on the age of the athletes. As for athletes involved in acyclic sports at step load power, age did not affect their heart performance. The threshold of adequate hemodynamic response of athletes under load was influenced by sport, rather than age. The application of the coefficient of comprehensive assessment of the cardiorespiratory system indicated the presence of large functional capacities of athletes engaged in cyclic sports.

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Corresponding author: kaf.fv.kgau@mail.ru