Step-count accuracy of three motion sensors for older and frail medical inpatients

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McCullagh, Ruth
Dillon, Christina B.
O'Connell, Ann Marie
Horgan, N. Frances
Timmons, Suzanne
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Elsevier B.V.
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Objectives: To measure the step-count accuracy of an ankle-worn accelerometer, a thigh-worn accelerometer and one pedometer in older and frail inpatients. Design: Cross-sectional design study. Setting: Research room within a hospital. Participants: Convenience sample of inpatients aged ≥65 years, able to walk 20 metres unassisted, with or without a walking-aid. Intervention: Patients completed a 40-minute programme of predetermined tasks while wearing the three motion sensors simultaneously. Video-recording of the procedure provided the criterion measurement of step-count. Main Outcome Measures: Mean percentage (%) errors were calculated for all tasks, slow versus fast walkers, independent versus walking-aid-users, and over shorter versus longer distances. The Intra-class Correlation was calculated and accuracy was visually displayed by Bland-Altman plots. Results: Thirty-two patients (78.1 ±7.8 years) completed the study. Fifteen were female and 17 used walking-aids. Their median speed was 0.46 m/sec (interquartile range, IQR 0.36-0.66). The ankle-worn accelerometer overestimated steps (median 1% error, IQR -3 to 13). The other motion sensors underestimated steps (40% error (IQR -51 to -35) and 38% (IQR -93 to -27), respectively). The ankle-worn accelerometer proved more accurate over longer distances (3% error, IQR 0 to 9), than shorter distances (10%, IQR -23 to 9). Conclusions: The ankle-worn accelerometer gave the most accurate step-count measurement and was most accurate over longer distances. Neither of the other motion sensors had acceptable margins of error.
Walking , Dimensional measurement accuracy , Frail , Elderly , In-patients
McCullagh, R., Dillon, C., O’Connell, A. M., Horgan, N. F. and Timmons, S. (2016) ‘Step-count accuracy of three motion sensors for older and frail medical inpatients’, Archives of Physical Medicine and Rehabilitation, 98(2), pp. 295-302. doi: 10.1016/j.apmr.2016.08.476