## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**FA State Indicator** & **T** & \(p\) & **Cohen’s d** & **TE State Indicator** & **T** & \(p\) & **Cohen’s d** \\ \hline ART & \(-2.481\) & \(0.023\) & \(0.516\) & & & \\ \hline DHR\_AVG & \(4.705\) & \(0.000\) & \(1.042\) & & & \\ \hline RTOS\_AVG & \(-7.971\) & \(0.000\) & \(1.829\) & & & \\ \hline RTOS\_SD & \(-5.941\) & \(.000\) & \(1.363\) & & & \\ \hline \end{tabular}
\end{table} 
Table 4: _Cont._to varying degrees; subsequently, their working performance was degraded. The paired comparison of AFT vs. ATE, AFT vs. AFA, FT vs. FA, and FT vs. TE also showed that fatigue had more significant effects on heart rate and reaction ability than tension. In this study, fatigue refers to the sleepiness resulting from the drive to sleep [27]. It is supposed that when ATCOs feel sleep, their physical subconscious tends to require them to sleep rather than allocate enough energy to support their work, resulting in the disabling manifestations on some of their abilities [13], a reduction in alertness, judgement, and reflex ability [1], and the impairment of their cognitive functions [61]. According to these results, the main influence mechanisms may have been that the ATCOs' fatigue caused a lack of motivation and slowed down physiological and cognitive functions, as well as their working performance. The order of the indicators of tension shows that tension has the strongest influence on DHR_AVG, followed by STT, DHR_SD, RTOS_SD, and ART, also indicating that physiological characteristics are affected first, followed by physical abilities. The results show that the DHR of the ATCOs was higher when they were tense in the workplace, but there were no significant differences in the HR between the BAL and ATE situations. The likely reason is that tension is a transitory state which occurs when complex task demand exceeds an ATCO's ability [51], and the level of tension decreases after leaving the workplace [47]. Therefore, tension occurs primarily during working hours, resulting in no significant differences in most of the indicators between the ATE and BAL situations. The lower STT and higher ART may show the residual or continuous effects of tension on concentration and decision-making abilities. Meanwhile, the comparison analysis of FT vs. FA and FT vs. TE indicated that tension had a dominant effect on the stability of heart rate. The participants stated that they were occasionally tense only when the control task was complex in the tension experiments, rather than during the entire experiment. Their heart rates were higher only in these situations and resulted in a higher DHR_SD. The response speed to the pilot's requests was highly variable, leading to a higher ROTS_SD. It was also reported that ATCOs might make some temporary decision errors [6] and forget flights [7] when they are tense. Based on these results, it is inferred that tension is a transitory state during working hours and causes instability in the ATCOs' physiological function and mistakes in working performance. The results of this study reveal the effect characteristics of fatigue and tension on ATCOs, especially the effect orders and the influence mechanisms of them. It provides references for improving the safety of air traffic control in practical applications. On the one hand, the results facilitate the evaluation of fatigue and tension so that management strategies or countermeasures can be developed. For example, in order to decrease the fatigue and tense state, circadian rhythmicity, sleep duration, ability, and task complexity should be considered in the shift arrangement. Tension should be closely monitored in high traffic flow conditions or complex control task scenarios. In state assessment and management, the ranking of the indicators indicated that physiological parameters should take priority as the measurement indicators. The influence mechanisms could also provide a reference for state assessment based on the performance of air traffic control.