## 2 Materials and Methods
### Data Acquisition and Analysis  
We used a single force plate (model 9260 AA; Kistler, Winterthur, Switzerland) to collect ground reaction force data at 1000 Hz. The data were processed automatically in the manufacturer's MARS software (version 4.0; Kistler, Winterthur, Switzerland). After low-pass filtering (Butterworth, 2 nd order, 10 Hz), the data were further automatically processed in the same software to obtain the mean CoP velocity (total, anterior-posterior (AP) and medial-lateral (ML)), CoP amplitude (AP and ML) and CoP frequency (AP and ML). The CoP amplitude was defined as the average amount of CoP sway in the AP or ML direction, which is calculated as the common length of the trajectory of the CoP sway (in AP and ML direction) and divided by the number of changes in movement direction. The CoP frequency was defined as the frequency of oscillations of the CoP calculated as the number of CoP signal peaks in the AP or ML direction (i.e., changes in the direction of CoP movement) divided by the measurement time. Firstly, we calculated traditional whole-trial estimates by averaging CoP characteristics over the entire trial. Additionally, we calculated the relative differences between the 1 st and the 2 nd (DIF_21) and the 1 st and the 3 rd (DIF_31) 10 s time intervals. These relative differences were expressed as percentages, with 100% representing no change, >100% indicating an increase between the 1 st and 2 nd (or the 1 st and 3 rd) time intervals and <100% indicating a decrease between the 1 st and 2 nd (or the 1 st and 3 rd) time intervals. The DIF_21 and DIF_31, using 10 s time intervals, were chosen in accordance to previous studies that showed that these indexes potentially bear  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Task** & **Descriptions of the Tasks and the Transition to the Task Positions** \\ \hline \multirow{4}{*}{Parallel EO} & Participants assumed the parallel stance position on the force plate and closed their eyes. The eyes were opened (as instructed by the examiner) after 15 s, simultaneously with the start of the data recording. The arms were hanging loosely at the sides. \\  & Participants assumed the parallel stance position on the force plate. After that, they closed their eyes (as instructed by the examiner) simultaneously with the start of the data recording. The arms were hanging loosely at the sides. \\ \multirow{4}{*}{Parallel EC} & Participants assumed the parallel stance position on the force plate. After that, they closed their eyes (as instructed by the examiner) simultaneously with the start of the data recording. The arms were hanging loosely at the sides. \\  & Participants stood with their feet parallel, at the posterior edge of the force plate. When ready, they \\ \multirow{4}{*}{Tandem} & Participants stood with their feet parallel, at the posterior edge of the force plate. When ready, they \\  & transitioned the dominant leg forward and assumed the tandem stance. The data recording started manually \\ \multirow{4}{*}{Single-leg} & 1 s after they assumed the tandem position. The hands were placed on the hips. \\  & Participants stood with their feet parallel, at the middle of the force plate. When ready, they transitioned the weight to their dominant leg, assuming a single-leg stance. The data recording started \(\sim\)1 s after they assumed \\ \multirow{4}{*}{Single-leg} & this position. The hip of the free leg was at 0\({}^{\circ}\), and the thigh was parallel to the standing leg, while the knee \\ \cline{1-1}  & was flexed at \(\sim\)90\({}^{\circ}\). The hands were placed on the hips. \\ \hline \hline \end{tabular} EO—yes open; EC—yes closed.  
\end{table}
Table 2: An overview of postural tasks performed in the study.  
some information independent from the whole-trial estimates [11; 15]. Our preliminary analyses (not published) also indicated that 10 s interval data generally exhibit acceptable reliability (ICC = 0.6-0.8), while 5 s data do not.