Validity of measuring the sit to walk movement with an inertial sensor

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 [1]. Research to date has confirmed the inherent difficulty of the STW movement [2]; however the technology used is limited to laboratory settings. Accelerometers may provide a suitable alternative.

Aim:

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, USA).  Participants performed three STW movements at self-selected speeds; normal slow 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 0.064s ± 0.05s for seat-off, 0.072 ± 0.063s, for swing-off and 0.063s ± 0.039s for swing-down. Agreement for the events was excellent with ICC 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 thigh mounted inertial sensors for recording time events during the STW movement, suggesting clear potential for this technique.

Support:

Development grant from School of Health, Glasgow Caledonian University