PhD, Associate Professor A.E. Chikov¹
Dr.Med., Associate Professor D.S. Medvedev^{1, 2}
PhD, Associate Professor S.N. Chikova^1
1Research Institute of Hygiene, Occupational Pathology and Human Ecology FMBA Russia, St. Petersburg
²St. Petersburg I.I. Mechnikov State Medical  University, St. Petersburg

Keywords: energy supply for muscular activity, mechanical efficiency rate, Wingate test, fatigue index.

Background. The main physiological factors limiting the implementation of short-term work of maximum intensity include the possibilities of energy supply for muscle activity and the possibility of neuromuscular transmission of efferent and afferent impulses [3, 8].

In our opinion, the physical working capacity test rates evaluated based on the metabolic energy rates during work (the so-called "energy" approach) may help differentiate the potentialities of energy supply for muscular activity and neuro-muscular transmission of afferent and efferent impulses and, accordingly, evaluate the dependence of the test rates on each of these factors. The “energy” approach involves the study of the pattern of energy generation and transformation, estimation of power of active energy metabolism, which, in terms of depletion, is transformed into mechanical power of muscle contractions [14]. Research works of this kind were carried out mainly in competitive swimming [2, 4, 12].

Objective of the study was to rate and analyze the energy inputs to the muscular activity and neuro-muscular transmission of afferent and efferent impulses by the Wingate tests.

Methods and structure of the study. Sampled for 265 test sessions under the study were the 18-35 male Class I-III athletes specializing in cyclic and acyclic sport disciplines and weighing 79.1±0.47kg on average. Each athlete was examined by medical experts to qualify for the Wingate test on cycle ergometer Monarch Ergomedic 894E. Based on the test results, we calculated mechanical power of performed work Pto_avg, Pto_max, Pto_min, mechanical index of fatigue described in literature as fatigue index (FI), active energy metabolism power rates Pai and the main forms of ATP resynthesis (aerobic, alactic, lactic), energy index of fatigue (FIe).

Energy indicators were calculated based on the oxygen consumption rate registered prior to, during and after testing using the Oxycon Pro gas analyzer; the blood lactic acid levels were assessed at rest and during the 3rd minute of recovery (Dr. Muller "Super GL compact").

Energy and power of active energy metabolism were evaluated according to the energy consumption formula proposed by V.L. Utkin [10] and described in detail in our research works [11, 13].

E_ai= (VО_2tot-VО_2res•t)•20,9 +ΔLa•0.0624•m₀/p                                                  (1) +(VO_2bor-0,55•m₀/70)•20.9•0.6 +0.55•m₀/70•20.9,

where E_ai – energy of active metabolism (kJ); VО_2tot – rate of oxygen consumption during work, l; VО_2res – rate of quiescent oxygen consumption prior to testing (l/min); t – execution time (min); VO_2bor  – rate of oxygen consumption during the first 2 min of recovery beyond quiescent level; ΔLa – difference between blood lactic acid levels prior to and after testing (mmol/l); m₀ – subject’s body mass; р=1.0 – body density (kg/m³); 20.9, 0.0624, 0.6 – estimated coefficients, 0.55 – oxygen storage coefficient.

The proposed formula was decomposed:

E_aiO₂ = (VО_2tot-VО_2res • t) •20.9                                                                   (2)

E_aiLa=ΔLa • 0.0624 • m/p                                                                            (3)

E_aiaLa= (VO_2bor-0.55 • m/70) • 20.9 • 0.6                                                    (4)

where E_aiО₂ – energy of active metabolism in terms of aerobic resynthesis of ATP, kJ; E_aiLa – energy of active metabolism in terms of lactic resynthesis of ATP; E_aiaLa – energy of active metabolism in terms of alactic resynthesis of ATP.

The power of active energy metabolism and the main forms of ATP resynthesis were evaluated with due regard to the execution time.

The test data were processed by Statistica-10 software, with the test data normality rated by the Shapiro-Wilk test, and with every rate in excess of 2s was removed from the sample to increase its consistency.

Results and discussion. The gas analysis and lactometry rates calculated according to the formulas 1-4 enabled to obtain the quantitative rates of energy supply and power of each of the main forms of ATP resynthesis during the Wingate test (Table 1).

Table 1. Indicators of metabolic energy generation and power of the main forms of ATP resynthesis during Wingate test

The ratio between the main forms of ATP resynthesis shows that it is the anaerobic form that requires the greatest amount of energy: 935.2±12.64 W - lactic (40.0%) and 807.2±7.58 W - alactic (35.0%). The remaining 25.0% of energy falls on the aerobic ATP resynthesis and available oxygen storage. The index of energy of active metabolism and components of the main forms of ATP resynthesis into the power of active metabolism is due to the need to reduce all the analyzed indicators to a single unit of measure along with mechanical power - Watt (W). This makes it possible to measure the efficiency of transformation of metabolic energy into mechanical power.

Metabolic energy is calculated according to the formula:

,                                                                                                 (5)

where e_g – metabolic energy coefficient, Pto_avg – average mechanical power throughout the Wingate test, Pai – average power of  active energy metabolism.

According to the findings, the average power of the work performed was 590.4±5.63 W, the total energy supply capacity (Pai) during the execution was 2323.0±20.98 W (Table 2), the mean metabolic energy coefficient was 25.6±0.19%.

Table 2. Mechanical power and power of energy metabolism during Wingate test

Similar quantitative values of metabolic energy e_g were obtained by А.А. Viru, M.V. Mishchenko [1, 6].

Further analysis was carried out with the following assumptions that do not contradict modern ideas of biomechanics:

• The metabolic energy coefficient values did not change significantly throughout the Wingate test, which was due to the nature of the work performed (the technique and intensity of pedaling did not change). This made it possible to measure the power of alactic ATP resynthesis based on the maximum mechanical power values ​​registered during the 3rd-5th min of Wingate test, when the energy supply for muscular activity was ensured mainly by the alactic ATP resynthesis, which deployment rate equaled 1-2 sec [5, 7, 9].

Therefore, given that the mean value of the maximal mechanical power was 944.7±11.70 W, and metabolic energy - 25.6±0.19%, the average power of the alactic ATP resynthesis was 3712±44 W (see Table 2).

• At the end of the test, i.e. during the 30th sec, the potentialities of alactic ATP resynthesis were exhausted, its power decreased sharply, and energy supply was ensured mainly by anaerobic glycolysis and aerobic phosphorylation.

Therefore, the minimal energy capacity was calculated as the sum of equivalents of oxygen consumption and level of final blood lactate, and equaled 1958±18.0 W (see Table 2).

The study enabled to obtain the quantitative values of two indicators characterizing the dynamics of decreasing physical working capacity:

1. mechanical index of fatigue (in literature referred to as fatigue index) that helps evaluate the degree of mechanical power reduction during the Wingate test;
2. energy index of fatigue, which characterizes the reduction of energy capacity and helps evaluate the degree of decrease in energy capacity during the Wingate test.

During the test, the mechanical power value (0.65±0.005) resulted from the reduced energy supply and onset of fatigue along the neuro-muscular pathway. The decrease in energy capacity (0.47±0.004) was due to the limited forms of ATP resynthesis - a decrease in the rate of ATP resynthesis as a result of exhaustion of alactic resynthesis, relatively low deployment rate and capacity of the lactic and aerobic forms. According to the research findings, the mechanical index of fatigue was significantly higher (p<0.001) than the energy one.

The data obtained are consistent with the research model designed basing on the fact that in the Wingate test the onset of fatigue is not only due to the decrease in the ATP resynthesis rate, but also due to the reduction in the efferent and afferent impulses of neuro-muscular transmission. This was proved by the fact that the amount of energy produced by the lactic and aerobic ATP resynthesis during the 30th min of testing exceeded the amount necessary for the set minimal mechanical power. This assumption was confirmed by the correlation analysis (see Figure 1).

Figure 1. Correlation relationships between the mechanical and energy indices of fatigue and the power of work performed (—– direct statistically significant relationship, - - - reverse statistically significant relationship)

The main difference between the mechanical and energy indices of fatigue is that the former is associated with the minimum power. While the energy index of fatigue directly correlates with the average and maximal power, and this correlation is statistically significant, which also makes sense considering the above data. Therefore, the maximal and average mechanical power depend on the energy supply capacity, while the energy supply mechanisms do not affect significantly the minimal power. It follows that the onset of fatigue at the final stage of testing is due to the exhaustion of potentialities of neuro-muscular transmission of efferent and afferent impulses.

Conclusion. The short-term maximal-intensity work efficiency generally depends on two factors: energy supply system and the neuro-muscular transmission of afferent and efferent impulses. In this view, the biomechanical test data generated by the Wingate test make it possible to differentiate the potentialities of energy supply for muscular activity and the neuro-muscular transmission of afferent and efferent impulses. The working capacity limitation factors may be purposefully modified by the training system management tools to step up the training system efficiency and, hence, the athletic fitness.

References

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10. Chikov A.E., Medvedev D.S. Mekhanizmy energoobespecheniya myshechnoy deyatelnosti pri vypolnenii standartizirovannykh nagruzok sportsmenov [Muscle energy supply mechanisms in athletes when performing standardized loads]. Sportivnaya meditsina: nauka i praktika, 2017, vol. 7, no. 2, pp. 19-24.
11. Fernandez‐del‐Olmo M., Rodriguez F.A., Marquez G., Iglesias X., Marina M., Benitez A., Vallejo L., Acero R. M. Isometric knee extensor fatigue following a Wingate test: peripheral and central mechanisms. Scand J Med Sci Sports. 2013. 23(1). pp. 57-65.

Corresponding author: chikov.alexandr@yandex.ru

Abstract

The main physiological factors limiting the implementation of short-term work of maximum intensity include the possibilities of energy supply for muscle activity and the possibility of neuromuscular transmission of efferent and afferent impulses.

Objective of the study was to rate and analyze the energy inputs to the muscular activity and neuro-muscular transmission of afferent and efferent impulses by the Wingate tests. Sampled for 265 test sessions under the study were the 18-35 male Class I-III athletes specialized in cyclic and acyclic sport disciplines and weighing 79.1±0.47kg on average. Each athlete was examined by medical experts to qualify for the Wingate test on cycle ergometer Monarch Ergomedic 894E. The test data were processed by Statistica-10 software, with the test data normality rated by the Shapiro-Wilk test, and with every rate in excess of 2s was removed from the sample to increase its consistency. The study data and analyses gave us the reasons to conclude that the short-term maximal-intensity work efficiency generally depends on the following key factors: energy supply system and the neuro-muscular transmission of afferent and efferent impulses. Biomechanical test data generated by the Wingate test make it possible to differentiate the energy supply system and the neuro-muscular transmission of afferent and efferent impulses. The working capacity limitation factors may be purposefully modified by the training system management tools to step up the training system efficiency and, hence, the athletic fitness.