An accelerometer-based method for estimating fluidity in the sit-to-walk task

[Purpose] The purpose of this study was to clarify the validity of accelerometer data for quantifying fluidity during the sit-to-walk task. [Subjects] The participants were 16 healthy young males. [Methods] The timing of events (task onset, maximum trunk inclination, and first heel strike) was determined from the acceleration waveform and compared to the timing determined from a three-dimensional motion analysis (task onset, maximum trunk inclination) or foot pressure sensor data (first heel strike). Regression analysis was used to estimate the fluidity index (FI) from the duration between events and the magnitude of the acceleration peak. The task was performed at two speeds (comfortable and maximum). [Results] A comparison of the timings from two different systems indicated no systematic bias. Specific events could be identified from acceleration data using regression analysis under both speed conditions. In addition, significant regression equations predictive of FI were constructed using the duration between events under both speed conditions. The duration from the maximum trunk inclination to the first heel strike was the best predictor of FI. [Conclusion] Accelerometer data may be used to precisely and conveniently evaluate fluidity. The clinical utility of these data should be tested in elderly individuals or patient populations.