Phone Based Sit-Stand-Sit Movement Analysis


Falls are dangerous, prevalent and costly. The frequency of falling is considerably higher among elderly, being one of the major obstacles to their independent living. The projection of an aging population poses a severe burden to the health services; the financial exertion and physical requirements necessary to provide the current level of care to such a large projected population are far too great to be feasible.

Various ideas need to be produced by taking advantage of current technologies, allowing them to remain at home and carry on safely as normal. Several falling risk factors were identified and specific interventions were designed in order to reduce those risks.

However, they are only applied with low frequency, requiring experts and expensive equipment. In this report, a smartphone is proposed as a measurement instrument of Sit-Stand-Sit movement as it is a prerequisite of gait and of paramount importance for fall risk analysis.

By using the smartphone’s accelerometer and gyroscope sensors, an algorithm was built in order to analyze key features associated with the movement. Two tests for fall risk evaluation were implemented, the 5 times sit-stand-sit and 30 seconds sit-to-stand. To validate the algorithm, 20 young adults and 15 older adults performed both tests, collecting a total of 150 test recordings.

These recordings were also filmed in video to compare the features returned by the algorithm with those extracted from the videos. Transitional movements were correctly identified with a precision of 99,3 %, with average difference of 0.311 seconds in the total duration of the tests and 1.8 degrees of error in the trunk tilt.

There was also a clear distinction in the number of repetitions performed between young and old adults in the 30 seconds sit-to-stand test as reported in the literature. Results suggest that the smartphone can be used as a major strategy to improve fall prevention; their popularity is likely to continuously increase in the near future due to decreasing prices, thus projecting an overall acceptance being a great value for older persons and society.


Author: João Soares

Type: MSc thesis

Partner: Faculdade de Engenharia da Universidade do Porto

Year: 2012