Validity of Measuring the Sit to Walk Movement with an Inertial Sensor

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Background.Moving from sitting to walking (STW) is a functional movement that is sufficiently demanding to reveal early mobility problems that may be masked in other tests (Kerr et al., 2007). Research to date has confirmed the inherent difficulty of the STW movement (Magnan et al., 1996); however, the technology used is limited to laboratory settings. Accelerometers may provide a suitable alternative.Aim.This study aimed to test the concurrent validity of an accelerometer for measuring temporal parameters of the STW movement.Method.Following ethical approval, 15 healthy participants were instructed to stand up and walk from a chair while a motion analysis system tracked the 3D trajectory of reflective markers located on anatomical landmarks on the trunk and lower limbs. Concurrently, the acceleration signals of both thighs were recorded by two tri-axial accelerometers (DelSys, Boston, MA, USA). Participants performed three STW movements at self-selected speeds: slow, normal and fast. Time events for the STW movement (seat off, swing off and swing down) were identified from changes in the marker trajectories, as described in the literature, and points of inflection in the acceleration signals.Results.Across all speeds, there was an absolute difference of 0.064 seconds ± 0.05 seconds for seat off, 0.072 ± 0.063 seconds for swing off and 0.063 seconds ± 0.039 seconds for swing down. Agreement for the events was excellent with intraclass correlation coefficient values between 0.96 and 0.99. Agreement for the whole movement duration was 0.99.Conclusions.This study demonstrated excellent agreement between a motion analysis system and inertial sensors for recording time events during the STW movement, suggesting clear potential for this technique. Copyright © 2012 John Wiley & Sons, Ltd.

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