Reliability and validity of a smartphone-based application for the quantification of the sit-to-stand movement in healthy seniors

Introduction: Recently, it has been demonstrated that biomechanical parameters measured with accelerometers during everyday activities might provide early information about mobility in seniors. The use of smartphones has been suggested for this purpose. The aim of this study was to develop and validate a smartphone-based application for the quantification of the sit-to-stand movement (STS) in healthy seniors. Methods: Sixteen healthy seniors performed the STS with a smartphone first attached to the lower back and then to the sternum. The subjects' vertical ground reaction forces (VGRF) and vertical acceleration (VAcc) were recorded simultaneously using two force plates (reference standard) and the smartphone, respectively. VAcc data were converted to force; power was then calculated based on both force-time curves. Subsequently, the total movement duration (T-total), peak force (F-max), rate of force development (RFD) and peak power (P-max) were determined. Relative (intraclass correlation coefficient [ICC]) and absolute (standard error of measurement [SEM]) reliability were also calculated. For the variables showing strong reliability (ICC >= 0.75), Pearson correlation coefficients (r) between VGRF- and VAcc-derived data and one-sample T-tests for the mean differences were carried out. Results: In the sternal configuration, all variables showed strong reliability (range: 0.86-0.93), except the smartphone-derived parameter RFD (ICC = 0.43). F-max and T-total were found to be highly valid (r = 0.86 and 0.98, respectively). Conclusion: The results showed that the smartphone-based application can be used as a reliable and valid tool for the quantification of the STS in healthy seniors if the proposed protocol is followed. (C) 2014 Elsevier B.V. All rights reserved.