## 2 Materials and Methods
### Data Processing  
The motion tracking system recorded the spatial coordinates of the anatomical markers, from which joint angles were calculated using the Opensim (NIH Center for Biomedical Computation, Stanford University, Stanford, CA, USA) software's Inverse Kinematics toolbox (Table 1) [22]. To quantify the recorded folk dance sequences, the 30 s-long sessions were split into cycles; one dance session contained approximately 15 complete dance cycles. The analyzed dance cycle was defined from cross position to the next cross position (Figure 1), which could be clearly determined from the marker placed on the calcaneus (the marker was placed on the center of the heel, where the Achilles tendon attaches to the calcaneus bone) and tibia (the marker was placed on the shin bone near the midline of the lower leg), from which the vertical displacement of the heel and the distance between the two shin bones were analyzed simultaneously. The beginning of a cycle was defined where the two distance functions had local minima, and the cycle lasted until the next coincided with the local minima. This way, the dance cycle started with a cross position and was followed by a short counterclockwise leg swing (Figure 1: right leg). Then, the dancer changed his/her BOS and performed a jump while swinging his/her other leg clockwise (Figure 1: left leg), which again was followed by a cross position and a short leg swing counterclockwise (Figure 1: left leg). After the change in the base of support, the dancer performed a jump again while swinging his/her initial leg clockwise (Figure 1: right leg), which ended with a cross position. Therefore, the cycle ended with the second cross position as well. The average and the standard deviation of the joint angles of the knee joint and the flexion of the hip joint during a dance cycle for one subject are shown in Figure 1. The dominant leg for the subject shown is the right leg. The average of the ranges of joint angular motion (ROMs) for hip flexion, knee flexion, and pelvic tilt were calculated for each dance session. These angular parameters could be obtained in each dance cycle through the recorded dancing sessions from which the averaged ROMs values could be calculated. The ground reaction force (GRF) was also recorded during the dancing session; the maximum value of the resultant force was also calculated in each dance cycle. The GRF was normalized by the body weight, eliminating possible inhomogeneity within the group. The examined parameters with definitions are summarized in Table 1.  
The recorded static stability test was also processed after the measurements. The measured force magnitude (\(x\)-\(y\)-\(z\) component, where \(x\) is anteroposterior, \(z\) is mediolateral, and \(y\) is the vertical axis) and the resultant force's point of application (coordinates in the \(x\)-\(z\) plane) were used during the postprocessing procedure. The measurements were carried out with two force platforms; therefore, separate force and displacement coordinates were recorded for the right- (Force Plate No. 2) and the left- (Force Plate No. 1) hand \begin{table}
\begin{tabular}{l l c} \hline
**Parameter Name** & **Description** & **Unit** \\ \hline Average cycle time & Average duration of one dance cycle & seconds (s) \\ \hline Dominant knee joint angle (DK) & Dominant knee flexion-extension angle & degrees (\({}^{\circ}\)) \\ \hline Nondominant knee joint angle (NK) & Nondominant knee flexion-extension angle & degrees (\({}^{\circ}\)) \\ \hline Dominant hip flexion angle (DH) & Dominant hip flexion-extension angle & degrees (\({}^{\circ}\)) \\ \hline Nondominant hip flexion angle (NH) & Nondominant hip flexion-extension angle & degrees (\({}^{\circ}\)) \\ \hline Pelvis tilt (PT) & Pelvis tilt angle in sagittal plane & degrees (\({}^{\circ}\)) \\ \hline Normalized ground reaction force (GRF) & Ground reaction force normalized by body weight & (1) \\ \hline \end{tabular}
\end{table}