## 4 Discussion  
The results indicate that most of the parameters of the physical characteristics and abilities were significantly affected by the situations or states. Fatigue had an adverse influence on many characteristics and abilities. Similarly to the findings reported by [PERSON] et al. [16], the results of the HR and DHR_AVG show that the ATCOs' HR was lower in the fatigue state. ATCOs' work requires a high mental workload in several aspects, including perception, attention, information processing, and decision-making [51; 52]. The effects of fatigue on abilities during work could be analyzed according to the analysis results. Compared with the previous research [1; 14], this study showed the effect of fatigue on abilities with new indicators. All the research revealed the adverse effects of fatigue on ATCOs. The lower STT and ROA under the influence of fatigue indicate impaired tracking ability and a lower attention range, respectively. This means that ATCOs may lose their concentration on the status of flights or miss flights. The higher RTL and RTS indicate a decrease in the reaction speed and longer time to perceive information. The lower TDSA indicates that ATCOs may issue instructions later than the right moment. The higher ART demonstrates that ATCOs require more time to make correct decisions in different situations. The changes in these parameters imply the reduction in attention, perception, reaction time, and decision-making ability. The higher RTOS_AVG and higher RTOS_SD also indicate a decrease in comprehensive performance. Though the simple task did not induce obvious post-work fatigue, the significant differences in STT, RTL, RTS, ART, and ROA between the BFA and AFA situations clearly indicate that the ATCOs' abilities tended to be worse if they continued to work while being sleepy. It is recommended that if an ATCO feels sleepy, he/she should stop working immediately rather than insist a little longer even for simple tasks. The imbalance between ability and task demand is one of the main factors of job tension [51]. The tense states of the young male participants were induced successfully by designing complex tasks in this study. It was found from the results that some physical characteristics or abilities of the participants were significantly affected by tension. Compared with the previous research on the effects of tension with a subjective survey [6; 7], this study reveals it in more detail with objective parameters. The lower STT and higher ART indicate that the ATCOs' abilities to track moving objects and decision-making were degraded. The higher DHR_AVG and DHR_SD imply that the ATCOs' heart rate tended to increase, and the stability of their physical status decreased during work in the tense state. Although the RTOS_AVG showed no significant differences, the RTOS_SD was significantly lower in the tense state, indicating a decrease in the stability of responding to the pilot's request and the reduction in overall performance. Considering the short job experience and relative low ability of young ATCOs, it is suggested to evaluate the complexities of tasks and each young ATCO's ability firstly and avoid the imbalance between the task demands and ability in the shift arrangement of ATCOs. The ranking of the indicators of fatigue shows that fatigue had the strongest influence on HR, followed by RTOS_AVG, STT, RTOS_SD, DHR_AVG, RTL, ROA, RTS, ART, and TDSA. The decreasing order of indicators provides an understanding of the effect levels of fatigue on the characteristics. Since the HR represents the physical state, the results indicate that in the fatigue state, the ATCOs' physiological characteristics were affected firstly, and their attention, reaction speed, perception, and decision-making were all impaired