HRV (Heart Rate Variability) is affected by stress and supports its use in objective assessment of psychological health and stress (Kim et al., 2018). Stress measurements depend on many parameters and factors, but are mostly made according to fluctuations in HRV. When HRV is large and irregular, the SDNN value increases. Therefore, SDNN is an index of physiological resilience to stress. The most consistent finding associated with variation in HRV variables is low parasympathetic activity characterized by a decrease in HF (high frequency) and an increase in LF (low frequency). It has been determined that mental stress leads to increased predictability, RR interval regularity, and decreased complexity. This situation reflects a change toward more stable and periodic heart rate behavior under stress. It has been concluded that decreased HRV and suppressed parasympathetic activation increase vulnerability to future stress (Kim et al., 2018). Although the 50–65 bpm range is accepted as normal values for an adult, the artificial intelligence model evaluates deviations in heart rate by comparing them with the individual's general average and interprets accordingly. Therefore, the score is adjusted approximately according to regular differences occurring below or above the individual average, not according to fixed thresholds.
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