## 3 Results  
There were significant differences in the plasma concentrations of NO\({}_{3}\)\({}^{-}\) (\(p\) \(<\) 0.001) and NO\({}_{2}\)\({}^{-}\) (\(p\) = 0.007) between the groups during training (Table 2). The plasma concentrations of NO\({}_{3}\)\({}^{-}\) (\(p\) = 0.084) and NO\({}_{2}\)\({}^{-}\) (\(p\) = 0.647) did not change significantly over time. VO\({}_{2}\), RER, BE, and VE were not different between the groups (VO\({}_{2}\): \(p\) = 0.916; RER: \(p\) = 0.409; Figure 3) (BF: \(p\) = 0.562; VE: \(p\) = 0.607; Table 3) and no group\(\times\)time interaction was observed (BF: \(p\) = 0.989; VE: \(p\) = 0.711; VO\({}_{2}\): \(p\) = 0.837; RER: \(p\) = 0.753). The concentration of lactate in arterialized and venous blood changed over time (\(p\)\(<\) 0.001), but no differences were found (Lac\({}_{\alpha}\): \(p\) = 0.954; Lac\({}_{\upsilon}\): \(p\) = 0.839). The concentration of glucose in arterialized and venous blood changed over time (\(p\)\(<\) 0.001), but for Glu\({}_{\upsilon}\), there was group \(\times\) time interaction during TR (\(p\) = 0.002). Post hoc tests revealed no significant differences between the groups (Table 3). \begin{table}
\begin{tabular}{c c c c} \hline
**Time Point** & **Group** & **Nitrate (μM)** & **Nitrite (μM)** \\ \hline \multirow{2}{*}{Rest} & N & 234.3 \(\pm\) 66.7 * & 1.51 \(\pm\) 0.39 * \\  & P & 61.7 \(\pm\) 50.4 & 1.16 \(\pm\) 0.22 \\ \hline \multirow{2}{*}{Warm-up} & N & 244.4 \(\pm\) 78.5 * & 1.56 \(\pm\) 0.29 * \\  & P & 70.1 \(\pm\) 42.0 & 1.25 \(\pm\) 0.44 \\ \hline \multirow{2}{*}{5 th interval} & N & 246.4 \(\pm\) 74.6 * & 1.57 \(\pm\) 0.28 * \\  & P & 64.6 \(\pm\) 46.7 & 1.21 \(\pm\) 0.27 \\ \hline \multirow{2}{*}{20 th interval} & N & 251.3 \(\pm\) 71.2 * & 1.60 \(\pm\) 0.24 * \\  & P & 68.3 \(\pm\) 53.1 & 1.13 \(\pm\) 0.26 \\ \hline \multirow{2}{*}{35 th interval} & N & 254.3 \(\pm\) 71.7 * & 1.50 \(\pm\) 0.21 * \\  & P & 65.8 \(\pm\) 46.1 & 1.12 \(\pm\) 0.24 \\ \hline \multirow{2}{*}{45 th interval} & N & 249.2 \(\pm\) 68.6 * & 1.40 \(\pm\) 0.23 \\  & P & 71.4 \(\pm\) 44.9 & 1.21 \(\pm\) 0.28 \\ \hline \multirow{2}{*}{Cool-down} & N & 256.1 \(\pm\) 89.9 * & 1.54 \(\pm\) 0.36 * \\  & P & 67.6 \(\pm\) 47.4 & 1.15 \(\pm\) 0.20 \\ \hline \end{tabular}
* \({}^{*}\)Denotes significant differences compared to the placebo group.  
\end{table} 
Table 2: Plasma concentrations of nitrate and nitrite during the 5 th training session in the nitrate group (N) and the placebo group (P). No differences were found between groups in the concentrations of Na\({}_{\rm v}\) (\(p\) = 0.293), K\({}_{\rm v}\) (\(p\) = 0.180), and Hb (\(p\) = 0.094) or in HCT (\(p\) = 0.802) (Table 4). The plasma concentrations of CRN, XA, NH\({}_{3}\), and total protein are shown in Figure 4. The concentrations of all analytes increased over time (\(p\) < 0.001). For CRN (group: \(p\) = 0.741, group \(\times\) time: \(p\) = 0.981) and XA concentration (group: \(p\) = 0.718, group \(\times\) time: \(p\) = 0.345), no interaction or differences between the groups were found. For NH\({}_{3}\), there was significant group \(\times\) time interaction (\(p\) = 0.026). At the end of TR, the NH\({}_{3}\) concentration was higher in the N group compared to the P group (post hoc, \(p\) = 0.034). The plasma protein concentration changed significantly during TR (\(p\) < 0.001), but no interaction (\(p\) = 0.110) was observed. There were no differences between the groups (\(p\) = 0.527). The plasma UA concentration was not different between the groups (\(p\) = 0.794). UA changed over time (\(p\) < 0.001), but no interaction was found (\(p\) = 0.304). Figure 3: Oxygen uptake (**a**) and respiratory exchange ratio (**b**) (left, \(y\)-axis) and power (right, \(y\)-axis) during TR in the nitrate group (red) and the placebo group (black); no significant differences were observed between the groups. \begin{table}