## 3 Results  
The heart-rate variability (HRV) metrics exhibited significant alterations during the ultra-endurance race. In the time-domain analysis, the mean heart rate escalated, with marked fluctuations over the four days. Notably, the RMSSD and pNN50 metrics substantially decreased from their pre-event values on Day 1. In the frequency domain, LF Power increased while HF Power showed a decline, resulting in a notable elevation in the LF/HF ratio, especially on Day 2. The nonlinear domain also displayed shifts, with SD1 and SD2 metrics notably decreasing from pre-event values. Overall, the data reflects the physiological challenges and adaptations experienced by participants during the event (Table 1). Figure 2 shows the results of (a) flicker fusion, (b) handgrip; (c) weight; and (d) horizontal jump. There were no significant differences in flicker fusion (\(p\) = 0.121), handgrip (\(p\) = 0.956), or horizontal jump (\(p\) = 0.090). However, a significant difference was found in weight (\(p\) = 0.020), lowering from the first 67.00 \(\pm\) 6.44 kg to 64.77 \(\pm\) 5.77 kg in the fourth stage. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Pre-Event** & **Day 1** & **Day 2** & **Day 3** & **Day 4** & \begin{tabular}{c} **Cohen’s d** \\ **(Pre vs. Day 4)** \\ \end{tabular}  \\ \hline Time-domain & & & & & & \\ \hline Mean HR (bpm) & 70.0 \(\pm\) 15.2 & 91.9 \(\pm\) 15.3 & 95.8 \(\pm\) 18.3 & 88.3 \(\pm\) 10.7 & 95.1 \(\pm\) 11.4 & 1.65 \\ \hline Min HR (bpm) & 5  
Figure 2: Cont. On the other hand, no significant differences were found in glucose (\(p=0.670\)) and lactate (mmol/L) (Figure 3). Figure 3: _Cont_. Figure 2: Results for each stage showing **(a)** flicker fusion; **(b)** handgrip; **(c)** weight; and **(d)** horizontal jump. The black bars represent the average values across all participants, with error bars indicating the standard deviation. Individual results for each of the 3 participants are shown with lines. Regarding urine parameters, there were no significant differences in pH (\(p\) = 0.112), colorimetry (\(p\) = 0.142), glucose (\(p\) = 1.000), or creatinine kinase (\(p\) = 0.097) (Table 2). However, a significant difference was found in the protein values in the urine (\(p\) = 0.033). Post-event urine analysis over the four stages of the ultra-endurance race revealed changes in various parameters. The pH of the urine remained consistent between the first two stages and then increased to a constant value in the third and fourth stages. Urine colorimetry values, which provide a measure of hydration, demonstrated variability, indicating differences in hydration status over the stages. Interestingly, glucose and protein presence in urine showed stability in the initial stages, but a significant spike in proteinuria was observed post the third stage, which then decreased by the fourth stage. Creatinine kinase, a marker for muscle damage, was only available from the second stage onwards, showing a decreasing trend over the stages (Table 2). Table 3 presents the average body temperature measurements in \({}^{\circ}\)C from various body regions of three participants before and after the event. We found an increase in temperature in the face, chest, abdomen, and right and left arm, and a decrease in temperature in the right and left leg. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Units** & **Post-1 st Stage** & **Post-2 nd Stage** & **Post-3 rd Stage** & **Post-4 th Stage** & \(p\) \\ \hline pH urine & & 5.33 \(\pm\) 0.58 & 5.33 \(\pm\) 0.58 & 6.00 \(\pm\) 0.00 & 6.00 \(\pm\) 0.00 & 0.112 \\ Colorimetry urine & & 7.33 \(\pm\) 0.58 & 4.67 \(\pm\) 3.21 & 4.33 \(\pm\) 3.1 & 5.00 \(\pm\) 2.65 & 0.142 \\ Glucose urine & & 0 \(\pm\) 0 & 0 \(\pm\) 0 & 0 \(\pm\) 0 & 0 \(\pm\) 0 & 1.000 \\ Creatinine Kinase & \(\mu\)mol/L & n/a & 418.33 \(\pm\) 112.77 & 300.67 \(\pm\) 80.41 & 219.33 \(\pm\) 63.01 & 0.097 \\ Protein urine & & 0 \(\pm\) 0 & 0 \(\pm\) 0 & 343.34 \(\pm\) 271.34 & 53.35 \(\pm\) 40.40 & 0.033 \\ \hline \hline \end{tabular}
\end{table}