False Steps: Activity Monitors’ Mistakes

Washing and drying dishes may not be quite the same thing as taking steps with your legs — but to some machines, sometimes it is. A step-by-step investigation suggests that the electromechanical fitness trackers, which track how many steps people take, can vary considerably in what they count as a step. Details are in this report:

“When a Step Is Not a Step! Specificity Analysis of Five Physical Activity Monitors,” Sandra O’Connell, Gearóid Ó Laighin, and Leo R. Quinlan, PLoS ONE, vol. 12, no. 1, 2017: e0169616.

The authors, at NUI Galway, Ireland, write:

As step count is one of the most utilized measures for quantifying physical activity it is important that activity-monitoring devices be both sensitive and specific in recording actual steps taken and disregard non-stepping body movements. The objective of this study was to assess the specificity of five activity monitors during a variety of prescribed non-stepping activities. …

Methods — Participants wore five activity monitors simultaneously for a variety of prescribed activities including deskwork, taking an elevator, taking a bus journey, automobile driving, washing and drying dishes; functional reaching task; indoor cycling; outdoor cycling; and indoor rowing. Each task was carried out for either a specific duration of time or over a specific distance. Activity monitors tested were the ActivPAL micro™, NL-2000™ pedometer, Withings Smart Activity Monitor Tracker (Pulse O2)™, Fitbit One™ and Jawbone UP™. Participants were video-recorded while carrying out the prescribed activities and the false positive step count registered on each activity monitor was obtained and compared to the video.

Results — All activity monitors registered a significant number of false positive steps per minute… The Withings™ activity performed best, registering a significant number of false positive steps per minute during the outdoor cycling activity only. The Jawbone™ registered a significant number of false positive steps during the functional reaching task and while washing and drying dishes.

(Thanks to Neil Martin for bringing this to our attention.)

BONUS (possibly related): Martha Stewart’s step-by-step advice for how to wash dishes.