## 2 Materials and Methods
### Procedure
#### 2.3.3 Static and Dynamic Balance  
Retro-reflective markers used to collect the data from the Vicon(r) 3D motion capture system (Vicon, Oxford, UK) were adhered to the skin surface of specific bony prominences of the body using double-sided adhesive medical tape following the Vicon(r) Plug-in-Gait model. A set of markers was applied to the participants' bodies to test balance, i.e., the moving of the Centre of Shoulders and Centre of Pelvis. According to the requirements of the project, markers were placed on the following bony landmarks:  
* To obtain the Centre of Shoulders: two markers were placed on the right and left shoulder bony prominences. * To obtain the Centre of Pelvis: four markers were placed on the anterior and posterior superior iliac spinae for both the right and left sides. The Centre of Pelvis was defined as the centre of four markers on the pelvis and was used to approximate the Centre of Mass of the whole body. The Centre of Shoulders was defined as the middle point between two shoulder markers and was used to assess movement in the upper trunk. The test used to assess the static balance was the single-leg stance test with eyes closed, while the four-square step test was used to assess dynamic balance [22]. Participants were required to stand on their dominant leg with their eyes closed for as long as possible to test static balance. In addition, the participants were required to walk for four steps in two opposite directions (clockwise and return) and complete the sequences as quickly as possible. Five trials were collected before and after CLS, using the Vicon(r) 3D motion capture system with four force plates. Ten trials were the total captured trials of each static and dynamic balance test for each volunteer. The collection of data is shown in Figure 2.  
The static balance test was performed using the dominant leg. The dominant side was determined by asking the participant which leg is preferred to stand on or which hand they used when writing. During data processing, the start and finish events were determined by the non-dominant foot off and on the ground during the static balance test. For example, if the participant preferred standing on the right leg as the dominant side, then the first foot strike (the last moment of touching the ground), foot-off, and the second foot strike (the first moment of touching the ground again) were collected from the left leg. For the static balance test, the time between the first and last heel strikes on the force platforms was used to calculate the balance duration, as shown in Figure 3.  
Figure 1: T-pose: subject with markers. Shoulder and trunk markers used for balance analysis. For the dynamic balance trials, right and left contexts (which are called clockwise and return events) were labelled for all trials, with events including first foot touch, foot-off, and second foot touch in each. The full sequence of walking along the force plates is the main aspect of assessing the dynamic balance by calculating the time of each context, either the right or left leg. For the right leg (clockwise cycle), the context was labelled depending on the full sequence, from the first touch of the second force plate, foot-off until the first strike of the last force plate (the first force plate), which was called the clockwise cycle, while the left leg cycle (return cycle) was from the first touch of the fourth force plate in the opposite direction, foot-off until the first strike of the last force plate (the first force plate), as shown in Figure 4.  
Figure 3: The single-leg stance test. Note: (**A**) The first foot strike: the non-dominant foot left the ground and the duration started. (**B**) The foot-off: the foot in the air. (**C**) The second foot strike: the non-dominant foot touched the ground, and the duration finished. Figure 2: Static and dynamic balance tests before and after 20 min of CLS. Currently, there are many different tests available. The two selected tests are commonly used. These tests are easy to perform and reflect balance ability very well.