M.S. Golovin, postgraduate student
R.I. Aizman, professor, Dr.Biol., Honored Worker of Science
Novosibirsk State Pedagogical University, Novosibirsk

Keywords: audio-visual stimulation, heart rate variability, cyclic athletes

Introduction. Development of methods of restoration and correction of functional states during sports activity is one of the principal goals of sports science. It helps train athletes for the upcoming sports events and in their effective recovery after competitions. Currently there are many methods of stimulation of the body of athletes intended to increase stress resistance and improve functional state. The effect on the body of athletes of various factors was investigated [6,12]. The instrumental methods of stimulation of the human functional state, technologies based on biofeedback [8,13,14] etc. are being actively developed. However, the method of audio-visual stimulation (AVS), widely spread in the West, has been successfully established in Russia primarily in the area of comprehensive rehabilitation [9,10] and correction of psychogenic disorders [1], addiction treatment and prevention of disorders in persons with professions related with danger and hard work [4]. However, studies of the effect of audio-visual stimulation in sports activities, characterized by excessive physical and mental loads, are almost lacking.

When carrying out rapid assessment and dynamic control of adaptive and reserve capabilities of athletes the analysis of heart rate variability at rest and during functional tests can be considered the most objective, informative and sensitive method for studying functional state and physical fitness [7]. The method is a modern and universally recognized indicator of assessment of the mechanisms of regulation of the cardiovascular system. Thus, the goal of our research was to study the impact of the audio-visual stimulation training course on the state of autonomic regulation and heart rate variability of athletes.

Materials and methods. Using the audio-visual stimulation method, operating by means of emission of binaural sound and flarelights, it is possible to change the bioelectrical frequency in the cerebral cortex within the functional state of a healthy body without side effects [1]. The investigation, consisting of 3 stages, involved 56 track and field male athletes aged 17-23 years, at the training stage, who specialized in middle distance race, first- and second-class athletes and those having a title of candidate master of sport. Sports training sessions were conducted 6 times a week. Running volume in different intensity zones amounted to 185-225 km/mos.

At the 1^st stage, we studied and analyzed heart rate variability with due regard to the methodological recommendations elaborated by the group of Russian experts [5]. The ECG-signal was registered using the hardware-software complex VNS-Micro (Neurosoft, Ivanovo, Russia) in the prone position (5 min) and right after standing up (6 min) in the II standard lead. Since the cardio-vascular system response to the orthostatic effects depends on the prevalent base type of autonomic regulation - sympathicotonic, normotonic and vagotonic [15, 16], the tension index of 30-90 c.u. was taken as a major criterion for express-estimation of the prevalent type of autonomic regulation [2]. For the purpose of investigation we selected athletes with the normotonic prevalent type of autonomic regulation only: control group (n=20) and experimental group (n=15). The athletes of the sympathicotonic and vagotonic types were excluded from the analysis. The membership of the examined groups was equal as for the percentage of athletes of different skill levels.

2^nd stage. The audio-visual stimulation (AVS) training course consisted of 20-22 sessions conducted every other day using the portable audio-visual stimulator "NOVO PRO" (USA). 2 programs were used: 1 - "keeping top competition shape", with prevalent stimulation frequency of 7-20 Hz and 30-min duration, which, according to the device certificate, activated the excitatory processes; 2 - "deep relaxation" with the prevalent stimulation frequency of 4-12 Hz and 25-min duration, resulting in predominance of inhibitory processes. For the athletes, who took the AVS course in the morning before training loads, the training course was delivered according to the first program, and after training loads - according to the second one.

3^rd stage. Upon completion of the AVS course, we studied the qualitative and quantitative changes in the heart rate variability indices in both groups at rest and during the orthostatic test.

All the obtained values ​​were processed by the common methods of mathematical statistics using the criterion of Wilcoxon-Mann-Whitney nonparametric test for independent samples and were considered reliable at p≤0.05.

The experiment was carried out in January-March, 2014, at the premises of the REC "Physiology of ontogenesis" of the Department of Anatomy, Physiology and Life Safety of Novosibirsk State Pedagogical University. All the surveyed gave a written consent to take part in the training courses, that were delivered in compliance with the Declaration of Helsinki (1964).

Results and discussion. Upon competition of the AVS courses, a tendency to the increase of the standard deviation (SDNN) with the normal values in the daytime ranging between 40-80 msec was observed in the athletes from the experimental group. There was a significant increment in the activity of the parasympathetic regulation (RMSSD), which normally ranged between 20-50 msec. The number of RR intervals over 50 msec (pNN50%) grew statistically significantly. In the control group the SDNN, RMSSD and pNN50% indices decreased considerably. At the same time, no significant changes were observed in heart rate and coefficient of variation (HR and CV; Table 1). Consequently, based on the findings of the temporary analysis, it can be concluded that after the AVS training, the effect of the sympathetic regulation in the body of athletes reduced, and so did the influence of the high level heart rate control. The contribution of the parasympathetic effects to the regulatory processes increased, and the autonomic regulation circuit was intensified. In the control group, for the same period of time, the contribution of the parasympathetic effects to the heart rate formation decreased, and the central regulation circuit was intensified.

The spectral analysis of heart rate in the athletes taking the AVS course has revealed a considerable improvement of the spectrum total power (TP), which may testify to the increase in the total activity of the neurohumoral effects towards heart rate. However, it was important to determine which frequency range contributed to these changes. As seen from Table 1, the power of very low-frequency (VLF) waves, characterizing the activity of the sympathetic nervous system and suprasegmental level of regulation, did not change significantly from January through March, while the values of low-frequency (LF - vasomotor) and high-frequency (HF) waves increased significantly. There was a decrease in the vagosympathetic balance (LF/HF) indices, as well as in the index of centralization (IC) of heart rate control, that characterize the reducing contribution of central mechanisms to heart rate regulation (Table 1). Therefore, it can be concluded that the AVS course promoted an increased effect of respiratory undulation on heart rate and its more efficient performance.

In the control group a significant decrease was marked in the total activity of the neurohumoral effects (TP) and in the contribution of respiratory undulation to variability formation, which can be explained by depletion of the parasympathetic regulation reserves during sports training. At the same time, the vagosympathetic balance indices and the index of centralization increased, indicating the intensification of tension of regulatory systems.

Variational pulsometry showed a reduction of activity of the sympathetic regulation unit (AMo) and tension index (TI) in the AVS group characterizing the degree of tension of the mechanisms of regulation. This influenced the autonomic balance index (ABI) value describing the relationship between the activity of the sympathetic and parasympathetic divisions of the autonomic nervous system (ANS), also we observed a decrease in the index of adequacy of regulatory processes (IARP). Extension of variation range (VR) in the AVS group testifies to the vagal regulation of heart rate. Thus, the tension of the regulatory systems and activity of the sympathetic division of ANS reduced upon completion of the AVS course. In the control group the changes were opposite: AMo, ABI, IARP and TI increased, while VR decreased. This indicates the heart rate stabilization and intensification of the sympathetic regulation.

Therefore, the variational pulsometry results complemented the values obtained during the temporal and spectral analyses, testifying to the positive effect of AVS on the intensification of the parasympathetic effects and an increment in the activity of the autonomic regulation circuit over the central mechanisms under rest conditions.

Table 1. Heart rate variability of track and field athletes (control and experimental groups)

Note. Significance of the intra-group differences in time history: * р<0,05; between the groups in January: #  р<0,05.

To determine the functional reserves of the mechanisms of regulation of ANS it is important to estimate heart rate variability (HRV) using functional tests. The orthostatic test is a significant method of determination of hidden changes on the part of the cardiovascular system, particularly, on the part of the mechanisms of autonomic regulation [3], and is used by many researchers to estimate the state of regulatory systems.

During the orthostatic test, the parameters characterizing the cardiovascular system functioning had the same differences in both groups as at rest. After the AVS course the indices of SDNN, RMSSD, pNN50% increased, while in the control group these parameters decreased considerably. This fact substantiates the earlier data on the intensification of the neurohumoral effects on the structure of heart rate after the AVS trainings.

The orthostatic test results obtained in the experimental group revealed an increase of TP and VLF, while in the control group these parameters decreased. This may testify to the exhaustion of the sympathetic regulation and occurrence of states of power deficiency when performing loads, while in the AVS group an increment in the total activity of the neurohumoral effects was marked. At the same time, we did not observe any changes in the parameters of LF, HF, LF/HF, which may indicate the influence of orthostasis on both of the divisions of ANS, but to different extent. However, a background study is needed to describe the detected changes more accurately.

The AVS course caused a decrease in the centralization of heart rate regulation and a reduction of tension of the mechanisms of regulation during the orthostatic test, which was testified by the increase of VR and the decrease of AMo, ABI, IARP and TI. In the control group the changes were opposite characterizing the tension of the mechanisms of regulation and the increase in the "value of the cardiovascular system adaptation to the orthostatic load.

Conclusion. Based on the research findings we can conclude that:

1) The ABS course contributed to an increase of the activity of the parasympathetic nervous system, an intensification of the effect of the autonomic regulation circuit, an intensification of the effect of the respiratory undulation on heart rate and more efficient performance at rest and during the orthostatic test.

2) In the athletes from the control group the tension of the mechanisms of regulation we observed, accompanied by an increment in the activity of the sympathetic nervous system, signs of exhaustion of the neurohumoral effects on heart rate and states of power deficiency, both at rest and during the orthostatic test.

3) The AVS training sessions can be recommended during sports activities to keep fit, recover faster and improve the functional state of the regulation mechanisms.

Therefore, one of the most relevant tasks is to develop and introduce into practice special methods and tools, which would help stimulate and correct the body systems. Herewith, they should be physiologically substantiated, easy-to-use and have no side effects [11]. By controlling the functional state, it will be possible to significantly improve the efficiency of professional activity. 

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Corresponding author: golovin593@mail.ru