## 3 Results
### Data Extraction  
The data extraction tables of the included studies are given in Tables 3-5. Figure 1: PRISMA flow diagram. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Study Name**} & \multirow{2}{*}{**Study Design**} & \multicolumn{4}{c}{**Demographics**} \\ \cline{3-6}  & & **Age Range** & **Sex** & \multicolumn{2}{c}{**Number of**} \\  & & & **Participants** & **County of Study** \\ \hline [PERSON] et al. (2021) [11] & Prospective Case Series & Over 60 years & Male and Female & N = 40 & Thailand \\ \hline [PERSON] et al. (2019) [12] & Prospective Case Series & 18–40 years & Male & N = 35 & Brazil \\ \hline [PERSON] et al. (2022) [13] & Prospective Case Series & 23–26 years & Male & N = 12 & China \\ \hline [PERSON] et al. (2007) [14] & Prospective Case Series & 18–35 years & Male and Female & N = 15 & Australia \\ \hline [PERSON] et al. (2008) [15] & Prospective Case Series & 20–25 years & Male & N = 20 & Brazil \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Study characteristics of incuded studies. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Study Name** & **Intervention Assessed** & \multicolumn{1}{p{113.8 pt}}{**Method**} \\ \cline{3-5}  & **Length of Intervention** & **Methodology of Collecting Data** \\ \hline [PERSON] et al. (2021) & Heart rate variability measurements taken in sitting, supine, and standing positions in this order & 10 min of both sitting and supine, 5 min of standing. The first 5 min of sitting and supine were disregarded to avoid extraneous factors. Total calculated duration was 15 min. & Three electrodes applied based on a two-lead method. ECG was taken with sampling rate of 1000 Hz using the PowerLab 26 T data acquisition system \\ \hline [PERSON] et al. (2019) [12] & Heart rate variability recorded in supine and orthostatic positions in this order & Volunteers laid on stretchers for 10 min before heart rate variability was measured for an additional 5 min. Then, they position for 2 min before HRV was measured for an additional 5 min. Total duration was 22 min. & Time series of the R-R intervals (calculated from an ECG) was performed using the POLAR® V800 monitor (Polar Electro 2024, Kempele, Finland). \\ \hline [PERSON] et al. (2022) [13] & Monitor seven trunk positions in the sitting position simultaneously & Each of the seven postures was held for 3 min, and the interval between each posture was 3 min. & NICOM (Non-Invasive Cardiac Output Monitor) was used to measure cardiac output, stroke volume variation, stroke volume index, cardiac index and heart rate \\ \hline [PERSON] et al. (2007) [14] & Cardiac parameters measured during prone-to-sitting and forcing positions & Participants would lie prone for 5 min then maneuver to a sitting or supine position for 5 min, which will be the period of data collection. The two interventions were conducted on two consecutive days. & Disposable electrodes were positioned, with the negative electrode over the pseudrocks at the left and right axillary lines. \\ \hline [PERSON] et al. (2008) [15] & Cardiac parameters measured during supine and sitting positions & Data were collected for 15 min for both the sitting and supine positions & Electrodes were positioned, with the negative electrode over the pseudrocks at the left and right axillary lines. Sample frequency of 500 Hz was used. \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Studies included in systematic review and what intervention was assessed alongside their methodology.