Dr.Biol., Professor R.V. Tambovtseva
Postgraduate V.A. Shelyakova
Russian State University of Physical Culture, Sport, Youth and Tourism (GTSOLIFK), Moscow

Keywords: aerobic endurance, oxygen, hemoglobin, metabolic state, anaerobic threshold, maximum oxygen consumption, test.

Introduction. Aerobic capacity of man is one of the main factors determining manifestation of endurance in relevant sports [2, 3, 7]. To date, a program of standardized tests and criteria used to assess aerobic endurance of athletes is developed [1, 2]. Most of the tests and criteria developed for assessing aerobic endurance of athletes are focused on carrying out accurate quantitative measurements of aerobic functions performance in laboratory and field conditions [1, 2, 3, 7, 8]. The method of near-infrared spectroscopy is an important one that is used to study the functions of aerobic metabolism at the organ level, tissue oxygen utilization and as a consequence determination of the effectiveness of body-wide aerobic capacity realization in athletes [4, 5, 6, 9]. However, there is almost no comprehensive research using the method of tissue spectroscopy to study aerobic capacity of athletes.

Objective of this research was to study the possibility of using the tissue spectroscopy method in the system of comprehensive assessment of aerobic endurance of athletes.

Methods and structure of the research. Subject to the study were 19 elite athletes specializing in cycling. All the subjects underwent testing in standard laboratory conditions. The program of standard laboratory tests included ones that allowed to carry out a comprehensive assessment of aerobic and anaerobic performance. Each subject performed three tests on a Monark ergometer (Sweden) – a step load test to failure, a maximal anaerobic power test and a Wingate test. МСЕ v.2.2 software provided the calculation of the following indicators: peak power (W), number of revolutions made during the test, total work completed during the test (kJ), maximum power (W), time of reaching maximum power (seconds), time of maintaining maximum power (seconds).

Results and discussion. Figure 1 shows an StO₂ curve of saturation of hemoglobin in the blood of one of the athletes involved in the experiment while performing a step load test. It is shown that StO₂ values remain almost unchanged for quite a long period of time followed by a breaking point, and the saturation of hemoglobin in the blood of the calf muscle starts to decrease gradually. Comparison of the load at which the reduction is observed with the anaerobic threshold value showed that these values fully concur. With further increase of the load after a certain time there comes a moment when StO₂ values start dropping like an avalanche and the minimum is reached at the time of failure. The culmination point of the avalanche-like decrease of StO₂ almost completely coincides with the time of reaching the respiratory compensation point (RCP). When the work is completed, restoration of the StO₂ values to their original numbers in the given athlete occurs within a very short period of time (about 1 minute). Such a response of the StO₂ curve was typical for half of the athletes under study, and all of them specialized in road racing and had high rates of maximum oxygen consumption (VO2 max) (>65 ml/min/kg). At the same time, the arterial blood hemoglobin saturation with oxygen showed that the StO2 value remained constant from the beginning to the end of the test in almost all athletes and fluctuated within a narrow range of 94-96%. Figure 2 shows a graph of changing StO₂ while performing a step load test of another athlete that participated in the experiment, but this time the sensor was secured on the biceps of the arm. Analysis of the StO₂ curve also showed the presence of two breaking points, but the slope of the curve after the second point is more gradual and the period of work till the failure is longer. Comparative analysis of the power of work at which these characteristic changes of the StO₂ value take place showed that these two points are completely consistent with the work power values at which anaerobic threshold and RCP are reached. This type of curve is typical for athletes having a relatively low value of VO2 max (<60 ml/min/kg) or for athletes specializing in sprint races. Comparative analysis of the nature of StO₂ values changes in the blood of the calf and biceps muscles during a step load test performed by the athletes revealed the presence of identical curves that differ neither by the formula not by the response amplitude. This fact indicates that StO₂ changes are systemic in nature and do not depend on whether the measurement took place in a working or idle muscle. Explanation of this phenomenon requires further research.

Figure 3 shows StO₂ dynamics in one of the athletes who participated in the experiment while performing a maximal anaerobic power test. StO₂ value decreases sharply from the first seconds of the work in the first repetition already, and after that is restored to almost baseline levels within 1 minute of rest. When the second repetition begins, StO₂ values drop sharply again, and the amplitude of the drop is much stronger than in the first repetition. Hemoglobin oxygenation in the working muscle is restored approximately following the same scenario during the recovery period after the second repetition as during the recovery period of the first one. From the beginning of the third stage of the test performance a decline in the degree of oxygen saturation is observed again, and the amplitude of the decline is the largest of all the three repetitions performed. Recovery of the hemoglobin oxygenation curve after the test completion is characterized by two phases – a fast one (of approximately a minute long) and a slow one (about 4 minutes long).

In connection with such changes in hemoglobin oxygenation in a working muscle it is of interest to study pulmonary ventilation of athletes while performing the test. Figure 4 shows the kinetics of pulmonary ventilation of the same athlete while performing the same test. It is shown that performance of the maximal anaerobic power test applies serious requirements to the external respiration system of athletes, and therefore to the energy supply of this type of work. During the first performance the pulmonary ventilation level increases relatively insignificantly in the course of the work, but it considerably increases within the first phase of rest, by the 40^th second of recovery reaches its maximum of 100 l/min and then drops by 20% to 80 l/min.

From the start of the second repetition the level of pulmonary ventilation begins to increase rapidly and by the end of the work reaches 120 l/min. The growth of this indicator continues for a few seconds during the recovery period (up to 138 l/min), and then there is quite a rapid decrease to 100 l/min. During the 3^rd repetition the pulmonary ventilation kinetics is almost exactly the same as that of the 2^nd one. Two pulmonary ventilation components are seen quite well during the recovery period – a rapid reduction to 85 l/min within 1.5 minutes and a slow decrease until the end of the observation. At the end of the recovery phase the level of pulmonary ventilation was 56-58 l/min, which is almost three times higher than the level of rest. Ventilation debt for 5 minutes of recovery (excluding breaks for rest between the repetitions) made quite a considerable value – 195 liters. Thus, performance of this test, which, according to a generally popular belief, was to be provided for by alactic energy sources, results in significant activation of external respiration, and hence oxygen delivery to working muscles. StO₂ value after the test completion is also characterized by two phases – a fast one and a slow one, but five minutes are not enough to reach the level of rest. The level of pulmonary ventilation reached while performing this exercise is relatively low and does not exceed 100 l/min, which is clearly lower than in the maximal anaerobic power test. This effect is probably due to the lack of breaks for rest that “rock” the external respiration parameters and ensure the achievement of high values of the pulmonary minute volume.

Conclusions

1. Breaking points in the StO₂ curve are almost completely consistent with the anaerobic threshold and RCP during the performance of the step load test.

2. StO₂ changes dynamics while performing muscular work correlates well with changes in the value of oxygen utilization in exhaled air.

3. Nature and amplitude of the StO₂ response are systemic and identical in both working and idle muscles.

4. Return to baseline oxygenation values after performing a step load test occurs within a short period of time (usually less than 60 seconds), in contrast to a maximal anaerobic power test and a Wingate test, after which this process can be as long as several minutes.

Figure 1. StO₂ graph of a subject when performing a step load test.

Y-axis - % of saturation of hemoglobin in the blood of the calf muscle.

X-axis - date and time of the test

Figure 2. StO₂ graph of a subject when performing a step load test.

Y-axis - % of saturation of hemoglobin in the blood of the biceps.

X-axis - date and time of the test

Figure 3. StO₂ dynamics of a subject when performing a maximal anaerobic power test (3x10 seconds, 1 minute of rest).

Y-axis - % of saturation of hemoglobin in the blood of the biceps.

X-axis - date and time of the test

Figure 4. Kinetics of pulmonary ventilation while performing a maximal anaerobic power test (3x10 seconds, 1 minute of rest).

Y-axis – pulmonary ventilation indices.

X-axis - date and time of the test

Abstract. Objective of this research was to study the possibility of using the tissue spectroscopy method in the system of comprehensive assessment of aerobic endurance of athletes. The experiment involved elite athletes, specializing in cycling, who underwent standardized laboratory tests. InSpectra^тм StO_2, a tissue spectrometer, was used to determine the correlation of hemoglobin saturation with oxygen in working and idle muscles. It was found that the degree of oxygen saturation of hemoglobin in the working muscles of athletes is strongly correlated with the indicators of aerobic energy metabolism at the body-wide level. Two breaking points are clearly seen on the curve of hemoglobin oxygenation in the muscles when performing a step load test. The first one coincides with the onset of aerobic-anaerobic transition (anaerobic threshold), and the second one - with the respiratory compensation point.

References

1. Belotserkovskiy Z.B. Ergometricheskie i kardiologicheskie kriterii fizicheskoy rabotosposobnosti u sportsmenov (Ergometric and cardiac criteria for physical work capacity in athletes) / Z.B. Belotserkovskiy. – Moscow: Sovetskiy sport, 2005. – 312 p.
2. Breslav I.S. Dykhanie i myshechnaya aktivnost cheloveka v sporte: rukovodstvo (Breathing and muscle activity in sport: guide) / I.S. Breslav, N.I. Volkov, R.V. Tambovtseva – Moscow: Sovetskiy sport, 2013. – 334 p.
3. Efimenko A.M. Kislorodny monitoring, porog anaerobnogo obmena (PANO), krovoobraschenie i dykhanie v otsenke funktsionalnyih rezervov organizma sportsmena pri vozrastayuschih nagruzkakh (Oxygen monitoring, anaerobic threshold (AnT), circulation and respiration in athlete's functional capacity evaluation under graded exercise) / A.M. Efimenko. – URL: http:// www.luganskorient.narod.ru/reabilit/PanoTavrYniv.htm. Date of access: 24.09.2009.
4. Mayers D. Neinvazivny lokalny metod opredeleniya nasyshcheniya gemoglobina kislorodom v tkanyakh posredstvom shirokopolosnoy spektroskopii v blizhney infrakrasnoy oblasti s ispolzovaniem vtoroy proizvodnoy spektra (Nonivasive local method of assessment of tissue hemoglobin oxygen saturation using second-derivative near-infrared spectroscopy) / D. Mayers, L. Anderson, R. Zayfert et al. // Zhurnal biomeditsinskoy optiki (Journal of Biomedical Optics). – 2005. – 10(3), 034017/1–18.
5. Transport gazov krovyu. Transport kisloroda. Kislorodnaya emkost gemoglobina (Blood Gas transport. Oxygen transport. Hemoglobin oxygen capacity). – URL: http:// www. http://meduniver.com/Medical/Physiology/431.html. Date of access: 25.10.2010.
6. Hatchinson Technolodgy Inc. InSpectra StO2. Monitor nasyshcheniya tkaney kislorodom (Tissue oxygen saturation monitor) // Use specification. – SShA, 2009. – P. 44.
7. Chinkin A.S. Osnovy podgotovki begunov na dlinnyie distantsii: metodicheskoe posobie (Long-distance runner training fundaments: guide) / A.S. Chinkin, M.N. Chinkin, F.R. Zotova. – Moscow: Fizicheskaya kul'tura, 2008. – 128 p.

Corresponding author: ritta7@mail.ru

Abstract. Objective of this research was to study the possibility of using the tissue spectroscopy method in the system of comprehensive assessment of aerobic endurance of athletes. The experiment involved elite athletes, specializing in cycling, who underwent standardized laboratory tests. InSpectraтм StO2, a tissue spectrometer, was used to determine the correlation of hemoglobin saturation with oxygen in working and idle muscles. It was found that the degree of oxygen saturation of hemoglobin in the working muscles of athletes is strongly correlated with the indicators of aerobic energy metabolism at the body-wide level. Two breaking points are clearly seen on the curve of hemoglobin oxygenation in the muscles when performing a step load test. The first one coincides with the onset of aerobic-anaerobic transition (anaerobic threshold), and the second one - with the respiratory compensation point.