Dr.Biol., professor R.V. Tambovtseva
Associate professor, Ph.D. J.L. Voytenko
Associate professor R.V. Yuriko
Russian state university of physical culture, sport, youth and tourism (GTsOLIFK), Moscow

Keywords: metabolic status, maximum power, lactic acid, exercise, aerobic, anaerobic, interval training.

Introduction. In sport practice, experts pay closer attention to the interval training modes aimed at the increase of aerobic and anaerobic performance of athletes [1,2,3,6,8,9]. Quantitative estimation and gradation of metabolic statuses of the body of athletes, which determine an urgent training effect, require efficient information about the integrative indicators of aerobic and anaerobic functions in response to variation in the parameters of physical load when performing repeated muscular work. The study of metabolic statuses, observed exclusively during exercises, as well as during various modes of repeated muscular work and in rest periods, is of great practical importance to the most efficient management of the training process. Metabolic status varies during muscular work and directly depends on such physical load parameters as: intensity and duration of exercises, number of repetitions and recovery time. When exercise intensity exceeds critical capacities, at which oxygen demand is higher than the maximum oxygen consumption, muscular work is performed mainly due to the functioning of anaerobic energy sources to produce a large amount of lactic acid and a heavy oxygen debt. It is well known that glycolytic processes are the most intensified in the time range between 30 seconds and two minutes of exercising, and there is maximum reinforcement of alactic process for ten seconds from the start of the exercise [2,4,5,6,7,9]. The duration of rest intervals between exercises has the most considerable impact on the nature of responses to physical load. The number of repetitions determines the extent of exposure of physical load on the body. When the body works in the anaerobic conditions, the number of repetitions increases, which leads to the depletion of energy reserves in the muscular tissue and the development of expressed fatigue. Increased concentration of lactic acid serves as a criterion of biochemical orientation of repeated training and indicates a progressive increase in the rate of anaerobic glycolysis. Exercises of maximum intensity in short-time periods of training and rest (up to 15 seconds) dramatically enhance anaerobic glycolysis in the working muscles during exercising [7]. By increasing the duration of rest breaks up to 30 seconds, it becomes possible to considerably resynthesize CP during rest breaks, and cover the remaining energy demand by means of aerobic processes, thus eliminating significant development of glycolytic reactions. In case of short-time repeated exercises of maximum intensity, the CPK system is the first to react to the emergence of free ADP, besides it fully controls the output of energy products in the first seconds of training. The CPK system capacity reaches its maximum values 2-3 seconds into the training. The formation of phosphocreatine at the early stages of training promotes an increase of glycolytic and aerobic processes. An urgent effect of interval training, of anaerobic glycolytic orientation in particular, differs from the level of development of aerobic and anaerobic abilities. Therefore, it is of interest to study the dynamics of metabolic status in case of 10 second repeated exercises of maximum intensity that would provide maximum activity of anaerobic alactic process during training with further switch to aerobic resynthesis of ADP during the rest intervals. In each particular case the variability in the duration of rest breaks will in a certain manner affect the degree of CP resynthesis and metabolic status.

Objective of the research was to study the influence of load on metabolic aerobic and anaerobic functions in case of ten-second repeated muscular exercise.

Methods and organisation. The experiment was conducted in the laboratory of bioenergy of muscular activity at the Sport Biochemistry and Bioenergy Department named after N.I. Volkov. 9 well trained cross country skiers were involved in the experiment. By the time of the examination, all the subjects were healthy and well-trained. Their sports qualification corresponded to the level of the first sports category. We employed ergometric and gasometric methods [1,4]. Anaerobic alactic power was evaluated by means of the modified test using the hardware and software complex "Ergomaks". For each testee we selected the optimal amount of load, at which they could develop and maintain the maximum cadence per ten seconds. Furthermore, we analyzed the variants of repeated load, where ten-second exercise periods alternated with rest breaks: 10, 30, 60 and 180 seconds. The concentration of lactic acid in the blood was measured by means of the enzymatic method using the photometric assembly "Doctor Lange" and the standard assay kit produced by "Beringer" (Germany). The blood samples were taken after 2, 4, 6, 8, 10, 15, 20 reps and immediately after exercising during the 3rd, 6th, 10th, and 20h minutes of the recovery period. The acid-base balance was measured using the microanalyzer of pH and blood gas produced by the "Instrumentation laboratory" company (USA).

Results and discussion. The conducted studies revealed that mechanical capacity when performing repeated exercises of maximum intensity decreases during the first 5-6 reps, which testifies to the progressive exhaustion of alactic anaerobic reserves in the muscles. After the first 5-6 reps, in the course of further performance of exercise, there is a rapid deceleration of the speed of loss of performance, which reflects activation of the mechanisms of glycolytic and oxidative re-synthesis of ATP, preventing further depletion of alactic anaerobic reserves of the body. Localization of the point of intersection of straight lines, characterizing these different metabolic statuses of the body, depends on the duration of the select rest breaks: the longer the rest break, the slower alactic anaerobic reserves are depleted at the initial phase of interval training. Based on this fact it can be argued that during the interval training of maximum intensity the total metabolic effect includes both the effect of rest breaks, and the effect of intensity of performed exercises. Performance of exercises of maximum intensity with 30-second rest intervals leads to a certain decrease in the "peak" values ​​of oxygen consumption (steady-state level of oxygen consumption during exercise is set at the level of 3.8 l/min). The kinetics of oxygen consumption during training and rest is the same as during the 10:10 exercise, The CO₂ value reaches its maximum of 1.6-1.7 l/min by the fifth rep from the start of exercising. In the course of the exercise we can observe a downward trend of this indicator during both training and rest breaks. Such kinetics of oxygen consumption during the 10-second exercise of supercritical intensity with rest breaks of 10, 20, 30 seconds was obtained during the experiments by Margaria [7]. The increase of rest intervals by 1 minute dramatically changes the dynamics of oxygen consumption. Simultaneously, we register a "delayed" increase in oxygen, observed shortly after the end of exercise during the rest intervals. The highest levels of oxygen consumption in this mode of interval training reach 2.5-3.0 l/min and are registered exclusively during the rest intervals. During exercise the oxygen consumption values are the lowest, and the release of CO₂ increases in all cases only during exercise. When performing 10-second exercises of maximum intensity with 3-minute rest breaks, there is a distinct peak of the "delayed" increase in oxygen consumption during the first minute of rest, followed by a decrease in oxidative activity.

Mitochondrial respiratory control can be based on the myofibrillar ATPase activity during work sessions, and upon completion - on the strengthening of the reverse reaction of CPK: C + ATP = CP + ADP. It is known that the highest level of activity of the reverse reaction of CPK is achieved during the 20th-30th seconds. Therefore, short-term rest breaks (up to 30 seconds) are not enough to restore alactic energy sources [9] and after 3-4 repetitions of maximum intensity the capacity of the CPKase reaction is exhausted and breathing is regulated mainly by means of the activity of myofibrillar ATPase when performing work sessions. Repeated exercises of maximum intensity provided the maximum share of fissionable macroergs every time, that is why varying rest intervals changed the share of macroergs, resynthesized in the aerobic process. During brief rest intervals, when macroergs recovered insufficiently, the phosphate acceptor pool increased continuously from repetition to repetition, and at the same time, the driver for rest strengthened. Therefore, the aerobic function responses graduate depending on the duration of the chosen rest breaks. If aerobic functions gradually respond to the changes in the duration of rest, the indicators characterizing an increase in the anaerobic glycolytic activity of the working muscles, when performing exercises of maximum intensity, remain stable and do not depend on the chosen rest breaks. However, there are significant differences only in the speed of reaching the peak level of anaerobic glycolytic activity. The stabilization of anaerobic shifts is observed in the studied modes of interval training of maximum intensity and is associated with increased rest breaks with a delayed increase in the glycolytic activity of the working muscles. Moreover, an increase in the glycolytic production during the rest breaks eliminates anaerobic shifts in the interval training of maximum intensity with different rest intervals. Longer breaks significantly enhance the role of anaerobic energy sources in the total energy balance of the exercise.

The dynamics of lactic acid in the blood is associated with the changes in the pH medium (Fig. 1). The maximum value of BE during these modes of repeated exercise does not exceed 16.5 mEq/l. At the same time, the data differ significantly from the mean values, which ​​primarily indicates the individual dynamics of anaerobic processes during repeated exercise, as well as the dependence of these indices on the intensity of exercises. The maximum values ​​of lactic acid obtained during our experiments agreed with the data obtained by R. Margaria [8] and N.I. Volkov [2,5]. A considerable level of lactic acid (up to 47 mg%) was observed at the beginning of the exercise, which could be explained by the triggering role of glycolysis, typical for the beginning of any muscular activity. Thereafter, the lactic acid concentration decreases and during the 20th minute of the recovery period returns to its initial value. The low level of lactic acid in the blood when performing ten-second exercise of critical intensity, alternating with ten-second rest intervals, is due to the prior use in the energy supply of oxidative reactions with the engagement of oxygen stored in myoglobin. The remaining oxygen debt is liquidated owing to the decomposition of high-energy compounds ATP, CP and anaerobic glycolysis in skeletal muscles. Lung ventilation when performing steady-state exercises increases significantly during ten-second rest breaks - up to 60-70 l/min within the exercise, and when performing other exercises - 10:30 - 39 l/min, 10:60 - 26 l/min, 10:180 - 22 l/min. When performing 10:180 exercise, at the end of rest intervals, the lung ventilation level reduces to that registered during the ​​rest - 8-10 l/min.

The conducted comparative analysis of the dynamics of metabolic functions in case of ten-second repeated exercise of various intensity with different rest intervals allows for the conclusion that metabolic responses differ due to the chosen load-rest (up to 30 seconds) ratio, at the same time, it is exercise parameters that are decisive for the modification of the metabolic response.

Conclusions

• In order to influence the anaerobic alactic mechanism during a ten-second exercise one should make an adequate choice of the number of repetitions of work sessions, and based on the invariables of the lactic acid accumulation rate the chosen number of repetitions are to be performed in series with long rest intervals.

• After 4-5 reps the metabolic status changed - we observed the critical depletion of alactic resources and the maximum level of anaerobic and glycolytic activity.

• The interval training modes, characterized by the highest rate of depletion of alactic reserves, could be set to increase the process efficiency.

• Serial interval training, consisting of 5-6 repetitions of maximum intensity, separated by long rest intervals up to three minutes, will have the most significant impact on the development of alactic anaerobic power.

• Interval training of maximum intensity, including three-minute rest breaks, contributes chiefly to the enhancement of alactic anaerobic capacity, which is achieved owing to the repeated significant depletion and subsequent reconstitution of alactic anaerobic reserves of the working muscles.

• The analyzed modes of interval training of maximum intensity contribute to the increase in the anaerobic glycolytic activity, but do not result in the maximum anaerobic glycolytic shifts.

References

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Corresponding author: ritta7@mail.ru

Abstract

Objective of the research was to study the influence of load on metabolic aerobic and anaerobic functions in case of ten-second repeated muscular exercise. 9 well-trained cross country skiers were involved in the experiment. Standard laboratory tests were applied. The state of the acid-base balance and the lactic acid concentration in the blood were determined. It has been established that when performing ten-second exercises with different rest breaks the variations in the metabolic activity differ substantially in its effect on the aerobic and anaerobic alactic energy conversion process. The maximum level of glycolytic activity is the same in case of multiple performance of work sessions. Significant differences are set only in the lactic acid accumulation rate. In order to influence the anaerobic alactic mechanism during ten-second exercise one should make an adequate choice of the number of repetitions of work sessions. And repeated work sessions are to be performed a chosen number of times in series with long rest intervals.