# Development of New Soft Wearable Balance Exercise Device Using Pneumatic Gel Muscles
## 2 Materials and Methods
### Participants and Measurement Protocol  
To assess reactive postural control during a balance exercise with the proposed device, seven healthy participants (six males and one female) participated in this study. The mean age of the participants was \(23.9\pm 2.0\) years. The participants' mean height was \(1.70\pm 0.08\) m, body weight was \(56.\pm 7.9\) kg, and foot length was \(0.26\pm 0.01\) m. Only participants with no history of lower limb surgery  
Figure 4: The PGMs in the soft wearable balance device control mechanism.  
and no pain during gait and single leg stance were included. Participant exclusion criteria included a history of neurological disorders and cardiovascular disorders.  
Measurements for the current study were performed in the following order: a pre-test, reactive postural control assessment session, an exercise session, and post-test measurement. The protocol of this study is shown in Figure 5. Participants were asked to perform a single leg stance as a measurement task in each session. Single leg stance task is one of the general assessments for balance function, and this task is frequently used for the assessment of fall prevention [25; 26]. In addition, single leg stance task is included in a clinical balance test such as berg balance test and BESTest as well as bipedal stance task. Participants were instructed to maintain their balance as consistently as possible during the single leg stance. During the single leg stance test, participants were asked to look at a sign 2 m away, which was placed at a height that corresponded to the height of their eyes, with their arms at their sides. Participants then performed a single leg stance using their dominant leg. The dominant leg was defined as the leg participants preferred to use to kick a ball [27]. To avoid the effects of auditory information, participants wore headphones and listened to music during the single leg stance in each session. In addition, all measurements were performed while participants were barefoot. The measurement task is shown in Figure 6  
Figure 5: Subject’s measurement task using wearable balance exercise device.  
The first session of the study protocol was the pre-test. Participants performed a single leg stance on their dominant leg. Five seconds after beginning the single leg stance test, acceleration data were recorded for 30 s. Next, participants were asked to perform a single leg stance while wearing the balance exercise device in the reactive postural control assessment session. Before the session began, an examiner checked the positions of the PGMs and the force generated by the trunk perturbation in each direction. In this session, participants underwent perturbation of their dominant leg direction by PGMs contraction during single leg stance, with no warning. Participants then underwent an exercise session. Five seconds after beginning the single leg stance test, interventions by the balance exercise device were initiated and lasted for 30 s. PGM perturbations induced by the examiner occurred four times between 5 and 25 s. The side and timing of the perturbations were randomized. This intervention was repeated five times. If participants felt fatigued, they were allowed to rest at any time. After completion of the intervention phase, the single leg stance test was performed as a post-test under the same conditions as the pre-test.