Balance is one of the most important issues that chronic stroke sufferers have to deal with. Balance assessment is needed to be taken to know the balance performance. However, assessing balance performance with existed objective methods (such as forceplate or biodex balance system) are not convenient and with subjective methods (such as functional tests or questionnaires) are not accurate enough. Smartphones had been proved effective in assessing balance, but new specific application is needed to be developed for subjects with chronic stroke. Therefore, the purpose of this study is to develop a smartphone-based balance assessment system for subjects with chronic stroke.

Android Studio was used to develop the balance assessment application. Six postures were designed to evaluate the balance performance: shoulder-width stance with eyes opened (E/O) and closed (E/C), feet-together stance with E/O and E/C, and semi-tandem stance with E/O and E/C. Each posture was tested for 30seconds, with a ASUS Zenfone 3 smartphone fixed at back on the level of second sacrum spine. The smartphone collected built-in accelerometer and gyroscope data to represent balance performance: the more data changed, indicated the more instability. The reliability test was executed after development of the application, and it included within-day (1-hour rest) and between-day (24-hour rest) assessments. Ten healthy adults were recruited. Intraclass correlation coefficient (ICC) was used to analyze the reliability, calculated by SPSS 20. Confidence interval was set as 95%.

The within-day ICC of the accelerometer data is 0.904 (P=0.000), between-day ICC is 0.764 (P=0.000); the within-day ICC of the gyroscope data is 0.897 (P=0.000), between-day ICC is 0.857 (P=0.000). The results demonstrate that the application is reliable.

The developed application is reliable to assess balance ability, and have the potential to be a convenient and valid alternative in assessing balance.