Abstract
Background There is limited information on reliable and valid measures of physical activity in older people with impaired function.
Objective This study was conducted to compare the accuracy of single-axis accelerometers in recognizing postures and transitions and step counting with the accuracy of video recordings in people with stroke (n=14), older inpatients (n=14), people with hip fracture (n=8), and a reference group of 10 adults who were healthy.
Design This was a cross-sectional study, evaluating the concurrent validity of small body-worn accelerometers against video observations as the criterion measure.
Methods Activity data were collected from 3 sensors (activPAL) attached to the thighs and the sternum and from registration of the same activities from video recordings. Participants performed a test protocol of in-bed, transfer, and walking activities.
Results The sensor system was highly accurate in classifying lying, sitting, and standing positions (100%) and in recognizing transitions from lying to sitting positions and from sitting to standing positions (100%). Placement of a sensor on the nonaffected leg resulted in less underestimation of step counts than placement on the affected leg. Still, the sensor system underestimated step counts during walking, especially at slow walking speeds (≤0.47 m/s) (limits of agreement=−2.01 to 16.54, absolute percent error=40.31).
Limitations The study was performed in a controlled setting and not during the natural performance of activities.
Conclusions The activPAL sensor system provides valid measures of postures and transitions in older people with impaired walking ability. Step counting needs to be improved for the sensor system to be acceptable for this population, especially at slow walking speeds.
Footnotes
Dr Askim, Dr Sletvold, Dr Indredavik, and Dr Helbostad provided concept/idea/research design. Mrs Taraldsen and Dr Helbostad provided writing and data analysis. Mrs Taraldsen, Mrs Einarsen, and Mrs Grüner Bjåstad provided data collection. Dr Askim and Dr Helbostad provided project management. Dr Sletvold and Dr Helbostad provided fund procurement and facilities/equipment. Mrs Taraldsen, Dr Askim, Dr Sletvold, Mrs Einarsen, and Dr Indredavik provided participants. Dr Helbostad provided institutional liaisons. Mrs Taraldsen provided clerical/secretarial support. Mrs Taraldsen, Dr Askim, Dr Sletvold, Mrs Einarsen, Dr Indredavik, and Dr Helbostad provided consultation (including review of manuscript before submission).
The authors thank the hospital staff at the Department of Geriatrics, St. Olav's Hospital, Trondheim University Hospital, and colleagues at the Norwegian University of Science and Technology for assistance with this study. They also thank all patients and volunteers who were healthy for taking part in this study.
The Regional Committee for Ethics in Medical Research in Mid Norway and the Norwegian Social Science Data Services approved the study protocol.
The health authorities of Mid Norway funded this study.
- Received May 11, 2010.
- Accepted October 16, 2010.
