## 4 Discussion
### Physical Stress
However, with AR instruction, the SD1 values for both simple and complex tasks remained unchanged. The findings of this study indicate that participants experienced higher levels of stress when engaging in paper-based instruction during the complex tasks compared to both the simple task and the AR instruction-based technique tasks. Hence, the use of AR instruction for executing complex tasks substantially alleviated the physical workload. The observed reduction in complexity measurements indicates a shift towards more stability and periodicity in HR during periods of stress. This shift might be associated with enhanced regularity, the separation of interconnected networks, and the inactivation of control mechanisms within the cardiovascular system [105; 106]. Such a decrease in HR complexity in response to stressful situations may indicate diminished flexibility and fitness of the cardiac pacemaker [107]. For the frequency domain variables of HRV, the results indicated that task complexity significantly influenced LF, HF, and the LF/HF ratio. As the task difficulty increased, HF decreased while LF and the LF/HF ratio rose. The results also showed that LF and HF/LF values were higher for the complex maintenance task while employing paper-based instruction, but HF values were lower. Moreover, performing the complex task using the paper instruction technique resulted in a higher HF/LF ratio and LF values and lower HF values compared to AR-based instruction. There was no significant difference between AR and paper-based instruction for the simple tasks, and no changes were seen between the complex and simple tasks when using AR-based instruction. This result is similar to those regarding the time domain of HRV, suggesting that the AR-based instruction technique was effective in dealing with increased maintenance task difficulty. The findings from the frequency domain parameters also showed that the mental and physical workloads for the challenging task were lowered by 46.27% when using AR instruction. The findings suggest that AR instruction is superior to paper instruction in boosting cognitive processing during complex tasks. The parasympathetic nervous system, which influences the effect of breathing on HR and is represented as HF power [108], is characterized by respiratory sinus arrhythmia [109]. Parasympathetic modulation causes a rise in HR [108], observed while carrying out the challenging task using paper-based instruction. A further decline in HF power was noted during the complex task using paper-based instruction. This decline can be attributed to alterations in the breathing pattern resulting from the adoption of uncomfortable postures, such as frequent bending and reaching while utilizing paper instructions. The observed rise in LF power during the complex task involving paper-based instruction could also be attributed to the adoption of uncomfortable body positions. According to a study by [109], changes in body position were shown to greatly enhance power within the LF range. Furthermore, elevated LF is noted in several scenarios, including a 90-degree tilt of the head when the body is in a supine position, standing, experiencing mental stress, moderate exercise among healthy individuals, and participating in physical activity [59]. This could explain the higher LF power values when performing a complex task using paper instructions. [PERSON] and [PERSON] [94] observed a 2.5-fold rise in the LF/HF ratio during high-intensity exercise compared to resting levels. The LF/HF ratio was employed as an indicator of sympathetic activity and HF power was utilized to indicate parasympathetic activity in the evaluation of work stress [98]. [PERSON] et al. [98] observed a significant increase in the LF/HF ratio and a decrease in HF power among those experiencing high levels of strain throughout workdays. This study also indicates that the LF/HF ratio exhibited an increase during the execution of complex tasks utilizing paper-based instruction, accompanied by a drop in HF power.