Physical activity as a health factor modifying heart rate variability (HRV)

Annotation: Purpose: The aim of the research was the evaluation of the selected HRV factors of the training volleyball players in two training periods and non-training people. Materials and methods: The study involved 8 leading volleyball players aged 20-23 and 13 non-training persons aged 19-26. The study of the training players was conducted twice: in the pre-competition and in the competition period. The study for the non-training persons was conducted once. The selected factors of the spectral analysis have been evaluated: TP [ms2], share of LF and HF power [n.u], LF/HF indicator and time analysis factors: RR [ms], HR [1/min], RMSSD [ms]. Results: Statistically significant differences appeared only in the selected time analysis factors (RR, HR), between the group of the training and nontraining persons. Other differences in the evaluated parameters were not statistically significant. Conclusions: Physical activity influences on the HRV growth. HRV measurement may serve for the control of the changes taking place in the AUN under the influence of the physical activity. Новосельска-Свадьба Данута, Зволинска Данута, Ендрисек Марек, Подставки Роберт. Физическая активность как фактор модификатора здоровья вариабельности сердечного ритма (ВСР). Цель: оценка отдельных показателей ВСР в течение двух периодов обучения тренирующихся волейболистов и неподготовленной молодежи. Материал и методы: В исследовании приняли участие 8 ведущих волейболистов в возрасте 20-23 года и 13 необученных лиц в возрасте 19-26 лет. Обследование тренирующихся спортсменов проводилось дважды в начале эксперимента и в конце. С неподготовленной молодежью испытание проводилось один раз. Оценены избранные показатели спектрального анализа: TP [ms2], доля мощности LF и HF [n.u], показатель LF/HF и временные показатели анализа: RR [ms], HR [1/ min], RMSSD [ms]. Результаты: статистически значимые различия наблюдались только в выбранных показателях временного анализа (RR, HR), между группой игроков и нетренирующейся молодежи. Другие различия в исследуемых параметрах не были статистически значимыми. Выводы: Физическая активность влияет на рост ВСР. Измерение ВСР может быть использовано для контроля изменений в вегетативной нервной системе под влиянием физической активности. Новосельска-Свадьба Данута, Зволинска Данута, Ендрисек Марек, Подставки Роберт Фізична активність як фактор модифікатора здоров’я варіабельності серцевого ритму (ВСР). Мета: оцінка окремих показників ВСР протягом двох періодів навчання волейболістів, що тренуються і непідготовленої молоді. Матеріал і методи: У дослідженні взяли участь 8 провідних волейболістів віком 20-23 роки та 13 ненавчених осіб віком 19-26 років. Обстеження спортсменів, що тренуються проводилося двічі на початку експерименту і в кінці. З непідготовленою молоддю випробування проводилося один раз. Оцінено обрані показники спектрального аналізу: TP [ms2], частка потужності LF і HF [nu], показник LF / HF і тимчасові показники аналізу: RR [ms], HR [1 / min], RMSSD [ms]. Результати: статистично значущі відмінності спостерігалися тільки в обраних показниках часового аналізу (RR, HR), між групою гравців і нетренованої молоді. Інші відмінності в досліджуваних параметрах були статистично значущими. Висновки: Фізична активність впливає на зростання ВСР. Вимірювання ВСР може бути використано для контролю змін в вегетативноій нервовій системі під впливом фізичної активності.

O'Sullivan S.E. and Bell C. [21] state that duration of the exercise, and/or training type affects significantly the value of the HRV factors.

Ethics
The study was conducted in accordance with the Helsinki Charter of Human Rights and it was approved by Ethics Committee of State Higher Vocational School in Raciborz. Each participant was willing to participate in the study voluntarily and confirmed that with a written agreement.
The study was conducted in the group of 8 contestants training volleyball. The study was carried out in two training periods: pre-competition and competition . The control group consisted of 13 physically inactive people.
The measurement of the tested persons was conducted with the use of Sport-Tester type Polar S 810i in the morning hours (7:00 -10:00). The subjects were instructed to avoid physical activity, maintain a current food intake, with the exception of the consumption of alcohol and caffeine for 48 hours before testing. On a test day, the athletes were on empty stomach and the HRV measurement were made in the lying down position. The record of the systoles frequency lasted 15 minutes. Standard test conditions were kept for all of the contestants (temperature 20-22 o Cthermo-neutral conditions) with keeping basic procedures compulsory in the sports metrology.
The record of the systoles frequency was transmitted to the computer memory and was processed in the statistics field with the use of the Polar Precision Performance 3 computer program, which is compatible with the HRV Analysis Software program (developed by The department of Applied Physics University of Kuopio in Finland). The methods of the spectral and time analysis were used for the development of the results. In the HRV Analysis program, the given incidence ranges were calculated: total power (TPthe range of the total power which is the sum of the ranges: ULF, VLF, LF, HF. The range between 0,01-0,5 Hz can be described as the sum of the ANS activity [22]), very Low Frequency (VLFa band ranging within 0,0033 Hz -0,05 Hz), LF (Low Frequencya band ranging within 0,05 Hz -0,15 Hz), HF (High Frequencya band ranging within 0,15 Hz -0.4 Hz) were calculated [23,24].
From all the registered parameters, for further analysis the following indicators were chosen: TP [ms 2 ], VLF [ms 2 , %], LF, HF [ms 2 , %, nu, the value LF/HF. In the time analysis were calculated: HR average [HR/min] systoles intensity. RR [ms]the average time RR intervals between sinus stimulations, RMSSD [ms]square root from the average sum of squares of differences between the next RR intervals [7,25].
According to many authors, the component HF reflects mainly the influence of the parasympathetic system (vagal influence) [26]. They prove in many studies that LF factor shows the influences of both autonomic system branches i.e. sympathetic and parasympathetic parts [11]. The values of LF and HF can be given in the normalized units (nu). According to Malliani [27], the power of the LF and HF spectrum, especially when expressed in normalized units, reflects the balance between sympathetic and parasympathetic control. Moreover, sympathetic-parasympathetic balance is evaluated by the LF/HF indicator [28]. Hynen E. [29] states that the interpretation of the LF/HF indicator is doubtful, but it is applied as an indicator of the voltage state of an autonomic nervous system. The average RR interval time is a derivative of the systole HR incidence. The RMSSD indicator reflects the tension of the parasympathetic system. The factors of the spectral analysis: HF and time analysis: RMSSD, pNN50% correlate with each other, depend directly proportionally on the vagus nerve tension [2].
The results of the HRV analysis were juxtaposed in tables making standard statistical calculations according to the descriptive statistics module. Arithmetic mean, standard deviation and the significance of the differences between particular groups were calculated. In view of the small group size (8 and 13 people) and in case of some parameters in which the distribution was strongly agonic, to calculate statistically essential differences between the groups the nonparametric U Mann-Whitney test was used to compare two independent groups. For the level of significance, the value of p˂0,05 has been accepted. The calculations were made in the Statistica Pl v. 10 program [30].   The evaluation by HRV of the changes taking place in AUN, affected by a long-term physical training volleyball players in the pre-competition and competition period and the control group showed that there were statistically significant changes in the field of the time analysis factors RR [ms] and HR [1/min]. In the physically inactive persons group there has been insignificant domination of the sympathetic part, in comparison to the physically active persons (LF n.u, LF/HF). In the volleyball players group, in the tested training periods, an insignificant growth in total power has been observed in comparison to the control group.

Discussion
Genetic and environmental factors affect a man's health [5]. Andrew M.E. et al. [31] state that physical activity and a proper diet can prevent diabetes, atherosclerosis, osteoporosis, circulatory insufficiency and other diseases. It must be emphasized that too intensive physical activity may trigger negative changes in the heart [32]. Numerous studies prove that a long-term endurance (oxygen) training cause changes in the sympathetic-parasympathetic balance in the sinus node and may cause a resting bradycardia observed with endurance athletes [33]. Stein R.M.C. et al. [34] state, in turn, that changes in the internal mechanisms of the sinus node, and not AUN, are responsible for a resting bradycardia. In our own research, there has been a decrease in heart rate with the volleyball players group, as a result of a long-term training. Both in the pre-competition and competition period, in comparison to the non-training group, decrease in heart rate (HR) and RR intervals showed a statistically significant difference. Baggish A.L. and Wood M.J. [35] state that heart rhythm disorders and changes in conduction, in trained athletes' heart are well known. According to the cited authors, sinus bradycardia of the contestants is asymptomatic. It is caused by an increased activity of the parasympathetic system, and especially an increased activity of the vagus nerve. However, some data suggest that systematic, hard, but not extreme physical training can lead to internal chronotropic changes of the sinus node. Some of the changes may be treated as lesions [36,37]. We cannot clearly determine where the heart's adaptive changes finish in response to a long-term, regular physical effort. It may be assumed that cardiac changes with the people practicing sports professionally, do not need to be adaptive changes [38]. In our own researches, decreased heart rate in the group of people with an increased physical activity, has not been proved by the spectral analysis factors. In the obtain tests results, both in the contestants' and control group, a sympathetic domination has been observed. However, in the contestants' group, in the tested training periods, an insignificantly lower tension of the sympathetic part has been observed in comparison to the control group. In the competition period, a period of a high physical activity, in the volleyball players' group, growth trends of the sympathetic part tension appeared in comparison to the pre-competition period. According to Iellamo F. et al. [20] growth of the sympathetic component, as a result of an intensified physical activity confirms good contestants' preparation for starts and achieving high performances. Authors quoted above state that longer maintaining of sympathicotonia can contribute to contestants' overtraining. Mourot L. et al. [39] confirm that too intensive trainings are connected with a balance shift in AUN towards sympathetic direction. The authors examined persons of a different physical activity (8 healthy men, 8 training, 7 with overtraining symptoms). On the base of the researches and the obtained results, it has been stated that the contestants with the overtraining symptoms showed an increase in sympathetic activity accompanied by the drop in parasympathetic activity and total power. Such a situation is connected with an overtraining of the Basedow type, which can appear with contestants [40]. Together with the training intensity reduction, the balance in AUN is restored. Nowosielska-Swadźba D [38]. examined boys aged 14-16 training athletics, volleyball and swimming. The results were compared to the physically inactive control group. A small domination of the sympathetic part has been marked in the control group. However, in the swimmers' group, subjected to more physical load, there has been a trend reversal, from a characteristic vagotonia to sympathicotonia. In our own research, in the control group, with the sympathetic domination, a shortened RR intervals have been observed and a high frequency of the heart rate in comparison to volleyball players group. LF and LF/HF factors testify the balance shift towards sympathetic direction in the control group. In the control group, the average value of the heart rate was 101,3/min and it was 41,1 beats higher in comparison to the people training volleyball. In the control group, sympathetic predominance, low total power value may be the result of the reduced physical activity [2]. Karjalainen j. et al. [41] write that tachycardia is caused, among others, by an increased activity of the sympathetic system. Rajab M. et al. [42] state that the reduction of high-frequency component (HF) in the total heart rate variability may be a diabetes complication, a risk factor for a sudden death.
Many researchers believe that physical activity shifts the AUN balance towards parasympathetic direction, through which it reduces mortality among others in cardiac diseases [2]. Nowosielska-Swadźba D. [38] examining boys aged 10-12 with the increased physical activity and physically inactive stated that in the experimental groups, there has been an increase in the heart rate variability. At the same time, in the group with an increased physical activity, longer RR intervals and lower heart rate frequency have been marked. Sacknoff d. M. et al. [43] examining trained people and a control group state, that an endurance training raises vagal activity, which is connected with a reduction of a resting frequency of heart rate. Levy W. c. et al. [44] were examining two groups of people, a younger one, aged 24-32 and older, aged 60-82. After a six-month sport training in the examined groups, they found a resting bradycardia through an increase in the vagal activity and sympathetic tension drop. A chronotropic activity drop has been observed. A resting HR drop and a growth of the resting HRV have been noticed in the examined group. Carter J.B. [45] came to similar observations examining mixed, recreational groups (6 men and 6 women) aged 19-21 and 40-45, in two periods before and after 12-month training. On the base of the heart rate variability record, he observed heart rate reduction and the total power growth with the examined persons. After the training period, the younger group showed a bigger growth of the total power. Melanson E.L. and Freedson P.S. [46] was examining men with the mean of age 36,6. After 16-month controlled, moderate power training, there has been a growth of the time and spectral analysis factors. However, many authors believe that HRV factors interpretation is often ambiguous. The surveys of the sportsmen showed that both HRV growth and drop can be connected with negative adaptation to exercise. Together with a positive adaptation of the circulatory system, a drop in the HRV value has been observed in the sportsmen group [47].
Evaluating somatic construction of the examined persons: physically active and non-training, it can be observed that body mass of the control group was lower in comparison to training group. Wierzbicka-Damska I. [48] writes that the main component of the body composition are: lean body mass (LMB -lean body mass), fat body mass (FBM-fat body mass), water content (TBW -total body water). Many authors state that long-term physical activity affects body composition (lean body mass participation, fat body) [49]. Systematic physical exercise reduces body fat and contributes to active tissue growth. On the base of the conducted studies and the obtained results it can be deduced that in the body composition, in the training persons group active tissue predominates. Evaluating weight-height factors (BMI, Rohr factor) in the examined groups, it can be stated that both groups have a proper body weight and athletic type. However, in the group with a reduced physical activity, BMI factor is at the limit of the standard and overweight while Rohr factor is at the limit of the athletic and pyknic type (WHO Raport www.WHO.com) [50]. In the examined control group, with the lack of physical activity, BMI growth trends may occur.

Conclusions
1. HRV is an important tool which can provide data about the modulatory influence of the AUN on the sinus node. 2. Under the influence of a long-term sport training, there appear changes in the sinus node which is reflected in a resting bradycardia. 3. Physical activity affects total power growth which has a positive effect on health. 4. Sport training influences on a balance shift towards parasympathetic direction. 5. Too intensive physical exercise strengthens sympathetic domination.