## 4 Result
### Subjective Stress and Workload Analysis
#### 4.2.2 Between-Group Differences  
Psychological stress was significantly linked to a decrease in the RR interval and an increase in the LF/HF ratio, suggesting a stronger dominance of sympathetic nervous system activity during stressful periods of the day [(38; 51)]. We analyzed whether varying levels of perceived stress were associated with changes in physiological responses. These features \begin{table}
\begin{tabular}{l c c} \hline  & **Indicator** & **PSS Score** \\ \hline  & - & PSS & 1 \\  & - & age & \(-\)0.2160 \\  & - & exp & \(-\)0.0663 \\  & - & mrrr1 & 0.0217 \\  & - & mrr2 & \(-\)0.1131 \\  & - & mrr3 & \(-\)0.1841 \\  & - & mrr4 & \(-\)0.2559 \\  & - & mrr5 & \(-\)0.3132 \\  & - & mrr6 & \(-\)0.2493 \\  & - & sdnn1 & \(-\)0.1975 \\  & - & sdnn2 & \(-\)0.1945 \\  & - & sdnn3 & \(-\)0.2283 \\  & - & sdnn4 & \(-\)0.2212 \\  & - & sdnn5 & \(-\)0.2329 \\  & - & sdnn6 & \(-\)0.2454 \\  & - & rmssd1 & \(-\)0.2682 \\  & - & rmssd2 & \(-\)0.1631 \\  & - & rmssd3 & \(-\)0.2276 \\  & - & rmssd4 & \(-\)0.1615 \\  & - & rmssd5 & \(-\)0.1976 \\  & - & rmssd6 & \(-\)0.1837 \\  & - & lfhf1 & 0.2647 \\  & - & lfhf2 & 0.432 * \\  & - & lfhf3 & 0.1582 \\  & - & lfhf4 & \(-\)0.0031 \\  & - & lfhf5 & 0.1127 \\  & - & lfhf6 & 0.2563 \\  & - & Mental & \(-\)0.0843 \\  & - & Physical & \(-\)0.0555 \\  & - & Temporal & \(-\)0.1008 \\  & - & Perf. & 0.2894 \\  & - & Effort & 0.1124 \\  & - & Frustration & 0.0902 \\ \hline \end{tabular}
\end{table} 
Table 10: Spearman correlation coefficients between various factors and perceived stress. were selected to measure the perceived stress on the navigators, under the condition that if they met normal distribution, then the one-way ANOVA could be explored. Across six segments, we first determined the mean value of each segment and found that the mean MRR has a significant effect on the perceived stress (\(p\) = 0.030), as shown in the Table 11.  
Through our exploration of each segment, the perceived stress showed significant differences in MRR on segment 2 (\(p\) = 0.032). We also found that the mean LF/HF ratio had a significant association with perceived stress (\(p\) = 0.015), as in Table 12. Figure 8 complements the ANOVA results by providing visual evidence of these physiological differences. The boxplot of the MRR values for segment 2 shows a notable reduction in RR intervals across increasing stress levels. Similarly, the LF/HF ratios increase across the PSS levels in segments 1, 2, and 5, supporting the role of sympathetic dominance in high-stress conditions. Segment 1 corresponds to crossing encounters at 090\({}^{\circ}\) port side and in head-on situations, while segment 5 corresponds to crossing encounters at 090\({}^{\circ}\) starboard side and 045\({}^{\circ}\) port side. Furthermore, the relationship between the perceived stress and mental workload (MW) was also explored using both TLX dimensions. However, no statistically significant differences were found in LF/HF ratios across workload levels. This contrasts with previous findings (e.g., [52]), suggesting that the workload, as measured in our study, may not have elicited sufficient variance to affect autonomic responses. To further interpret the statistical findings, boxplots were generated to visualize the distribution of physiological stress markers. The boxplot of the mean MRR revealed a downward trend from the low- to high-stress groups, supporting the idea that higher perceived stress is associated with reduced RR intervals. Segment 2 reached statistical significance (\(p\) = 0.032), suggesting elevated stress. For the LF/HF ratios, segments 1, 2, and 5 showed clear increases in sympathetic dominance (higher LF/HF values) across the rising PSS categories. The aggregated boxplot of the mean LF/HF values further affirmed this pattern, whereby individuals reporting high perceived stress levels consistently exhibited elevated LF/HF ratios.