## 4 Discussion and Implications
For animals of different species (including bottlenose dolphin weighing 50-250 kg) and humans (on land), the following relationship was obtained: \(P_{bi}=3.4\cdot m_{0}^{~{}0.74}\), \(20\cdot 10^{-3}<m_{0}<3.7\cdot 10^{3}\)[34]. The factor responsible for a slight increase in \(P_{bi}\) for swimmers is the water temperature (27-28 \({}^{\circ}\)C), which is not a thermoneutral zone for humans. As a result of the research, a dependence that takes into account an impact of the temperature factor of the aquatic environment upon basal metabolism was obtained: \(P_{bi}=3.7\cdot m_{0}^{~{}0.74}\), 55 kg \(<m_{0}<\) 95 kg [39]. For the conditions of human swimming, we formalized this approach as follows:  
\[P_{ai}=3.7\times m_{0}^{~{}0.74}\times v_{0\text{exp}}^{~{}3}\times C_{x(\text {ad})}\times e_{g}^{-1} \tag{7}\]  
where \(P_{ai}\), \(m_{0}\), \(v_{0\text{exp}}\), \(C_{x(\text{ad})}\) and \(e_{g}\) are the same variables as previously identified. Analysis of the calculated metabolic curves obtained on the basis of Equation (7) in all swimming techniques showed that relationships between \(v_{0\text{exp}}\) and \(P_{ai}\) obtained during swimming in humans are similar to those for warm-blooded animals, including for bottlenose dolphin [34; 35]. Regardless of the swimming technique, the value of maximum deviation of the experimental metabolic curve regarding the calculated dependence over the entire range of \(v_{0\text{exp}}\) does not exceed \(\pm 2\%\) for females and 4% for male swimmers. \(P_{to}\) values obtained for the four swimming techniques (Figures 1B and 2B) just slightly differed between swimming modes over the entire estimated range of \(P_{ai}\) values. Thus, for all swimming modes performed by females, at an energy input of \(P_{ai}=1000\) W, the difference between minimal and maximal values of \(P_{to}\) is less than 7 W, and at \(P_{ai}=2000\) W, the difference between swimming techniques is \(\Delta P_{to}<8\) W. With comparable values of \(P_{ai}=1500\) W, for all swimming techniques performed by males, the difference between minimal and maximal values of \(P_{to}\) is less than 25 W, and for \(P_{ai}\) values of 3000 W, \(P_{to}<16\) W. In addition, the \(P_{to}\) values over the entire studied range of \(P_{ai}\) values were markedly higher than the comparable values obtained for the female subjects, expressing expected gender differences. Consequently, total mechanical power should not be considered a relevant discriminant factor among the four swimming techniques. In all four swimming techniques, the mechanical efficiency (\(e_{g}\)) was in inverse linear dependence of \(v_{0\text{exp}}\), both for males and for females (Figure 3A,B), at least for the range of tested velocities. For aquatic locomotion, such a dependence may be easily understood from Equation (5) and in association with the conditions of the swimmers' propulsive segments' (arms, legs and, in some swimming strokes, the trunk) interaction with the aquatic medium. In contrast to terrestrial cyclic locomotion (walking, running), where the distal part of the propulsive segment interacts with a stationary surrounding, in swimming locomotion, a fluid medium is involved, which moves relative to the mover as a consequence of any action of the latter. Consequently, with increased swimming velocity, it is expected to obtain a higher value of P2--Equation (5)--expressing a higher amount of energy wasted to increase the kinetic energy of the water mass surrounding propulsive segments. The \(e_{g}\) values obtained in our study for the female swimmers at \(P_{ai}=1000\) W were in accordance with those observed during front crawl swimming at similar \(P_{ai}\) values by another experimental method: the MAD system [38]. A comprehensive quantitative and interrelated analysis of the studied variables' influence on \(v_{0\text{exp}}\) in various swimming techniques in female (Table 2) and male (Table 3) swimmers was performed for the last stage of the step-test, utilizing the model described in Equation (1).