I.D. Tupiev, associate professor, Ph.D., Head of the faculty of Physical Education
Ufa State University of Economics and Service, Ufa
S.V. Latukhov, candidate
Bashkir State Medical University, Ufa
D.Z. Shibkova, professor, Dr.Biol.
Chelyabinsk State Pedagogical University, Chelyabinsk

Key words: physical activity, physical working capacity, aerobic and anaerobic thresholds, bicycle ergometry, work power, cardiovascular system.

Introduction. It is known that currently diseases which are typical for senior people tend to be more frequently diagnosed in young people. This is due to the lack of physical activity of today's rising generation [7]. In order to increase physical working capacity (PWC) and functional capabilities of students, exercises of different power and intensity are implemented in physical education classes [1, 8]. The most popular ones are the so-called cardiovascular exercises which are prolonged cyclic exercises of low intensity (jogging, walking, etc.). Energy supply of such exercises is provided mainly due to the oxidative phosphorylation processes, and the effect of such exercises is aimed at the increase of the cardiovascular system performance and has been thoroughly studied. According to numerous authors [3, 6], moderate intensity running up to 1-2 minutes long, performed in cycles, is ideal for the development of endurance. Energy supply of this kind of work originates in the aerobic and anaerobic modes.

Currently the studies of the effects of static-dynamic exercises, distinguished by cyclic performance of low intensity movements with limited amplitude, without relaxation of contracting (mainly aerobic mode) muscles arouse the interest of researchers in the field of sport physiology [2]. Meanwhile, the physiological effects of physical exercises of maximum intensity done in the anaerobic-alactate mode for no more than 5 seconds are still understudied.

The purpose of the study was to investigate the physiological effects of physical loads of different intensity on female students who are not engaged in physical culture and sport.

Materials and methods. The study involved female 6^th-year students of the medical university (n=19, 22,5±0,2 years, 56,5±1,6 kg, 164,4±1,2 cm), proved to be healthy by the medical examination. As training exposure the subjects of the first group (M group, n=7) were to perform pedaling exercises on a bicycle ergometer with maximum tempo for 3-5 seconds, with 1-1.5-minute rest intervals, 10 reps. The total time on test was 11-16 minutes. 

The students of the second group (A group, n=6) performed pedaling exercises on a bicycle ergometer, keeping the power corresponding to the predetermined individual value of anaerobic threshold, for 1 minute, with 3-4-minute rest intervals. The number of reps - 3. Total training time - 9-12 minutes.

The subjects from the third group (S group, n=6) performed four static-dynamic exercises (half-squat and calf raises without full knee extension, hip raises without full hip joint extension, body raises with both feet flat on floor) in sequence, slowly and without relaxation, using the repeat-serial method. Each exercise was performed 30 times for 60 seconds, with 30-second rest intervals between the reps (3 reps). Total training time - 24 minutes. 

The experiment was conducted in vitro and lasted 10 days. The subjects had a complete physical examination at the beginning and at the end of the experiment. First, we registered the indices of the timed inspiratory capacity test (Stange’s test (ST) and Genche’s test (GT), sec), and vital capacity (VC, ml), using a dry spirometer. We calculated birth-death ratio (BDR=VC/M, where M - body mass, kg). Then, the step test was made, during which pedaling exercises on the bicycle ergometer Kettler 1X were performed, and at each stage work power (W, watt), heart rate (HR, bpm), and lung ventilation (LV, l/min) were measured [9]. The initial load equaled 25 W, every 1 minute the load increased by 20 W, pedaling tempo was 60 rpm. The testing was terminated if the subject was not able to keep the set pace during the whole minute, with that, the terminal work power (Wterm) was considered to be equal to the work power of the previous stage. At the end of the test the maximum values of HR (HRmax) and LV (LVmax) were recorded.

Maximum alactate muscle power (MAmP) was measured after 20-25-minute rest upon completion of the first test. For that purpose, the bicycle ergometer Proteus V6 was used, which was adjusted for the maximum resistance. The subjects tried to pick up full pedaling speed without getting up from a saddle of the bicycle ergometer. After 2-5-minute rest the test was repeated, and the maximum value of the registered effort power was chosen out of 3 attempts.

The values of PWC₁₇₀, aerobic (AET) and anaerobic (ANT) thresholds were determined within the rectangular coordinate system of the dependence of HR and LV on the load power [9]. The value of maximum cardiac output (COmax) and the percentage of oxidative muscle fibers (OMF) were calculated by the following formulas.

COmax=CO×HRmax, where СО=0,008×PWC₁₇₀ + 25 [4],

OMF =100 ANT/(MAmP – ANT) [6].

Statistical significance of differences was estimated by the non-parametric Wilcoxon, Mann-Whitney and Kruskal-Wallis tests using the software Statistica 6.1.

Results and discussion. Given that the majority of the subjects lead a sedentary lifestyle, the level of physical working capacity and functional fitness of the female students turned out to be low. Despite their juvenile age, the females got tired quickly after doing the exercises: the step test was terminated at the level of 100-120 W (4-5 minutes of work), for which low values of PWC₁₇₀ (80-110 W), load power at the aerobic and anaerobic threshold, and low MAmP values are typical (Table 1). The values of the respiratory samples of all the females corresponded to their age (Table 2).

Table 1. Changes in the indices of physical working capacity of the female students from the examined groups (М±m)

р_W and р_KW – statistical significance of differences as per Wilcoxon and Kruskal-Wallis, accordingly. Dash – absence of statistically significant differences

In all the groups, despite the differences in the training exposure, short-term performance of physical exercises and varied intensity of physical activity, a statistically significant increase was marked in the absolute and relative terminal load power. Concurrently, an increase was observed in the load power at the aerobic and anaerobic thresholds, and in Group M the anaerobic threshold increased statistically significantly. At the same time, the absolute value of PWC₁₇₀ rose significantly only in Groups M and C, and even decreased slightly in Group A. At the end of the experiment no statistically significant differences in this index were found in all the groups (χ²=6,06; р=0,048). Moreover, the percentage of the OMF in the performed work decreased in Group A and increased in Groups M and C. Such difference may be due to the fact that during the experiment the percentage of anaerobic glycolysis in the energy exchange, apparently, increased in the subjects from Group A. The formation of the glycolitic ATP limits the absorption rate of Са²⁺ by the sarcoplasmic reticulum [10], which results in the partial myocardium relaxation and consequently - the HR increase (Fig. 1). Accordingly, the CO value in Group A was stipulated by the increase in HR but not the systolic volume. Thus, CO decreased slightly on the average in Group A during the experiment (Table 2), which was accompanied by the statistically significant increase of the maximum HR. Meanwhile, in Groups M and C a statistically significant increase of CO was observed (with simultaneous slight increase of HRmax). The detected changes are indicative of the negative adaptive changes in the cardiovascular system in female students from Group A.

Maximum alactate muscle power (MAmP) increased in all three groups; however, owing to the specificity of the training sessions a more pronounced and statistically significant increase was observed in Groups M and A, obviously, these are the high-threshold motoneurons that were mainly stimulated in the subjects. In Group C the low-threshold motoneurons were mostly stimulated, which innervated the postural muscle fibers, resulting in the slightly changed MAmP.

The changes in the cardiorespiratory indices are represented in Table 2.

Table 2. Changes in values of cardiovascular and respiratory systems of female students from examined groups stipulated by physical exercises of different intensity (М±m)

During the experiment, vital capacity and birth-death ratio increased statistically significantly in Group M and changed slightly in Groups A and C. Besides, in Groups M and A a statistically significant increase was noted in the Stange and Genche’s test results, which suggests the enhancement of the hypoxia tolerance. 

Terminal power and maximum HR (at the final stage of the test) increased in all the groups, which implies the increase in the performance of active muscles and CVS. A statistically significant increase of maximum LV in Group A may specify that the nature of the training load contributed to the earlier involvement of the glycolytic muscle fibers in work. This may be proved by the decreased percentage of the oxidative MF in the performed work (Table 1). In Group M an opposite trend was observed: the maximum LV decreased, but the oxidative MF percentage in the performed work increased. In Group C, against the background of the increasing percentage of the oxidative MF, the maximum LV increased, too.

Besides comparing the mean values in each group, the individual responses of HR and LV to the gradually increasing load were analyzed (Table 3), revealing the differences in the process of adaptation to training load. Nine possible variants of these responses may be divided into four groups basing on the shifts in HR and LV and their tendencies (Fig. 1): 1) 3 variants of positive reactions (1-3), 2) indifferent variant (4), 3) uncertain (5 and 6), and 4) negative (7-9) [5].

Figure 1. Dependence of HR and LV on power value when performing a step test on bicycle ergometer (7 (unfavorable) variant of response of cardiorespiratory system)

The downward shifting of the HR₂ curve as compared to its initial level (HR₁) is indicative of the increase in the cardiovascular system’s performance (increase in systolic and cardiac output). The upward shifting of the curve proves the opposite and may be indicative of the failure in adaptation of the cardiovascular system. LV₂ curve shifting downwards or upwards against LV₁ proves accordingly an increase or a decrease in the aerobic performance of active muscles.

As seen from Table 3, radically different reactions to training exposure were observed in the examined groups. Thus, the favorable or indifferent variants of the cardiovascular system responses were registered in Groups M and C, and unfavorable only - in Group A. The detected tendency proves the earlier conclusion on the possible negative adaptive changes in the cardiovascular system of the students from this group.

Table 3. Distribution of female students from examined groups according to ratio between changes in HR, LV and terminal work power (Wterm)

Comments: Dcr – decrease, Unch – unchanged, Incr – increase

Conclusion. The use of physical loads of different intensity was proved to contribute to higher physical working capacity of virtually all female students. The physiological effects of the use of maximum and low intensity physical loads were close to each other. The positive effect of these loads was confirmed by the increase of girls' aerobic capacity and positive adaptation reactions of the cardiorespiratory system. Whereas the submaximal load (Group A) promoted a reduction of aerobic capacity of the cardiorespiratory system and caused unfavorable adaptive responses in the subjects. The revealed tendency towards the decrease of some indices of the functional state of the body along with the increase of the level of physical working capacity is not in line with the tentative hypothesis of the intended positive effect of physical activity performed at the level of the anaerobic threshold, and needs further examination.

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Corresponding author: ildustil@mail.ru