## 2 Subjects and Methods
Before each test stage and after performing in both conditions, blood samples were taken from  
Figure 2: Functional relationships between \(v_{\text{loop}}\) and \(P_{ai}\) (**A**), and between \(P_{ab}\) and \(P_{ai}\) (**B**) in the swimming pool 8 \(\times\) 100 m step-test for male swimmers in the four swimming techniques. Legend: M1 (24 years old, height—1.89 m, body mass—78.9 kg, \(V^{\prime}\)O\({}_{2 res}\)—0.28 L\({}^{-1}\), \(C_{\text{r}(\text{ad})}\)—0.365); M2 (23 years old, height—1.84 m, body mass—76.0 kg, \(V^{\prime}\)O\({}_{2 res}\)—0.27 L\(\cdot\)min\({}^{-1}\), \(C_{\text{r}(\text{ad})}\)—0.486); M3 (21 years old, height—1.86 m, body mass—73.0 kg, \(V^{\prime}\)O\({}_{2 res}\)—0.26 L\({}^{-1}\), \(C_{\text{r}(\text{ad})}\)—0.491); M4 (23 years old, height—1.94 m, body mass—89.5 kg, \(V^{\prime}\)O\({}_{2 res}\)—0.30 L\(\cdot^{-1}\), \(C_{\text{r}(\text{ad})}\)—0.605). swimmers' finger for peak capillary blood lactate concentrations' assessment using a biochemical analyzer \"Stat Fax 4500\" (\"Awareness Technology\", Palm City, FL, USA). To determine the total energy expenditure (\(E_{ai}\)) in both tests, the method of indirect calorimetry was used [5,13,15,16,17,18]. The experimental-theoretical approach was based on the results of a previous study using direct calorimetry of physical activity performed at various intensities by subjects on a bicycle ergometer using a bio calorimeter [19]. This approach is formalized as an equation for determining \(E_{ai}\), consisting of the sum of three components: aerobic (\(E_{ai(Aer)}\)), anaerobic alactic (\(E_{ai(AurAl)}\)) and anaerobic lactic components (\(E_{ai(Anl)}\)):  
\[ \begin{array}{ll}E_{ai}=(V\text{O}_{\text{2 tot}}-(V\text{O}_{\text{2 res}} \times t))\times\alpha+0.55\times m_{0}/70\times\alpha&\gets E_{ai(\text{ Aer})}\\ +(V\text{O}_{\text{2 bor}}-(0.55\times m_{0}/70))\times\alpha\times 0.6&\gets E_{ai(\text{ AnAl})}\\ +\beta\times\Delta La\times m_{0}&\gets E_{ai(\text{ AnAl})}\end{array}  \tag{2}\]  
where, \(E_{ai}\) is the metabolic energy input (kJ), \(V\text{O}_{\text{2 tot}}\) is the total amount of oxygen intake during the exercise (L), \(V\text{O}_{\text{2 res}}\) is the rest oxygen intake (L-min\({}^{-1}\)), \(V\text{O}_{\text{2 bor}}\) is the amount of net oxygen intake above the rest level during the first 2 min of recovery (L), \(t\) is the exercise duration (min), 0.6 is the coefficient of the \"phosphagen cycle efficiency\", \(\alpha\) is the energy equivalent for O\({}_{2}\), equal to 20.9 (kJ)-(L-min\({}^{-1}\))\({}^{-1}\)), \(\Delta La\) is the net lactate concentration after exercise (mmol-L\({}^{-1}\)), \(\beta\) is the energy equivalent of the accumulation of lactate in the blood, equal to 0.0689 (kJ-(kg-mmol\({}^{-1}\))\({}^{-1}\)), \(m_{0}\) is the body mass of the subject (kg) and 0.55 is the coefficient of \(\approx\)oxygen store of the body\({}_{9}\) for a person with a body mass of 70 kg [19]. When testing in the swimming flume, at each stage of the test, all three components of \(E_{ai}\) were determined based on direct measurements. In the pool test, on the other hand, \(E_{ai(AurAl)}\) and \(E_{ai(Anl)}\) were also determined based on direct measurements from capillary blood lactate concentrations and recovery \(V\text{O}_{2}\) values, but \(E_{ai(Aer)}\) was calculated taking into account the individual values of \(E_{ai(Aul)}\) and \(E_{ai(Anl)}\) obtained in the pool and the individual partial contributions of the main energy systems to \(E_{ai}\) obtained earlier in the flume for the corresponding intensity step of the swimming pool test. It should be noted here that the use of Equation (2) allows for determining \(E_{ai}\) over the entire range of swimming velocities attained by the swimmer in the step-test.