Step-Count Accuracy of 3 Motion Sensors for Older and Frail Medical Inpatients.

OBJECTIVE: To measure the step-count accuracy of an ankle-worn accelerometer, a thigh-worn accelerometer, and a pedometer in older and frail inpatients.

DESIGN: Cross-sectional design study.

SETTING: Research room within a hospital.

PARTICIPANTS: Convenience sample of inpatients (N=32; age, ≥65 years) who were able to walk 20m independently with or without a walking aid.

INTERVENTIONS: Patients completed a 40-minute program of predetermined tasks while wearing the 3 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, for slow versus fast walkers, for independent walkers versus walking-aid users, and over shorter versus longer distances. The intraclass correlation was calculated, and accuracy was graphically displayed by Bland-Altman plots.

RESULTS: Thirty-two patients (mean age, 78.1±7.8y) completed the study. Fifteen (47%) were women, and 17 (51%) used walking aids. Their median speed was .46m/s (interquartile range [IQR], .36-.66m/s). The ankle-worn accelerometer overestimated steps (median error, 1% [IQR, -3% to 13%]). The other motion sensors underestimated steps (median error, 40% [IQR, -51% to -35%] and 38% [IQR -93% to -27%], respectively). The ankle-worn accelerometer proved to be more accurate over longer distances (median error, 3% [IQR, 0%-9%]) than over shorter distances (median error, 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.