## 4 Discussion  
This systematic review consolidated the existing knowledge regarding the association between posture and heart rate variability in sedentary adults. The objective of the study was to determine how lifestyle modifications and therapeutic approaches can be adapted to improve autonomic function and overall health. Heart rate variability (HRV) is a widely recognized cardiovascular risk marker and provides insights into autonomic tone [16]. All five studies included in this review used frequency-domain analysis methodology to assess heart rate variability, facilitating comparisons despite variations in objectives and interventions. The overall findings from the analyzed studies indicate that the sitting position has a more pronounced impact on heart rate variability and other cardiac markers than supine and prone positions. [PERSON] et al. [17] examined different sitting positions (e.g., forward flexion, posterior extension) and examined their effects in detail. They found that the forward-leaning posture, which is commonly associated with office jobs and sedentary behavior, had the most detrimental impact on autonomic function. Meanwhile, [PERSON] et al. [12] concluded that reducing sedentary behavior may decrease mortality risk. [PERSON] et al. [11] focused on assessing the influence of sitting and supine postures on heart rate variability measurements. Their results indicated heightened autonomic responses in the sitting position, which is consistent with the findings of [PERSON] et al. [14] and [PERSON] et al. [15]. [PERSON] et al. [12] primarily aimed to identify behaviors associated with cardiac autonomic function by examining the impacts of vigorous and moderate exercise, sleep quality, caloric expenditure, and sedentary behavior on heart rate variability. Although components unrelated to posture were not addressed in this review, comparisons of the different effects on heart rate variability provided insight into the process between cardiac function and postural stability. In addition, even though the changes in heart rate variability were insignificant, the influence of sedentary behavior on heart rate variability was identified as the most significant variable associated with a higher mortality risk. This association underscores the importance of reducing time spent in a sedentary state, as it may contribute to poor long-term outcomes. A meta-analysis based on this study suggested that reducing daily sitting time to less than three hours can increase life expectancy by two years [18]. [PERSON] et al. [13] found that trunk posture changes can affect heart rate, cardiac function, and autonomic nerves. Specifically, posterior extension posture significantly increased heart rate and the LF/HF heart rate variability parameter, whereas trunk flexion posture, resembling a hunched sedentary position, decreased cardiac variables. These findings indicate that maintaining a neutral trunk position is optimal for stable cardiac function and balanced sympathetic tone. The results of [PERSON] et al. [13] provide insights into the relationship between posture and autonomic function and provide more specific findings regarding the impact of different spinal manipulations. [PERSON] et al. [14] found that heart rate variability parameters were less affected by transitions from the prone to supine positions than prone to sitting. Another study comparing cardiovascular parameters between the supine and prone postures showed more significant differences, which could be attributed to the sample size, by which the HRV analysis could not reveal related differences in autonomic regulation of the heart. The difference could also be due to methodological differences, as [PERSON] et al. had collected data just five minutes after posture changes [19]. It is essential to consider the time interval between data collection and changes in participant posture because these can affect the variables. Similar to [PERSON] et al. [13] and [PERSON] et al. [14], [PERSON] et al.