Activity monitor reliability and validity in community-dwelling older adults

Monitoring older adult physical activity is central to surveillance of individual and population health as well as delivery and evaluation of health promotion programs, and it requires reliable and valid measurement tools. I investigated step count test-retest reliability and criterion validity across consumer-grade activity monitors in community-dwelling older adults with and without self-reported mobility limitations during over-ground walking (n = 36; mean 71.4 years). I evaluated six activity monitors (Fitbit Charge, Fitbit One, Garmin vívofit 2, Jawbone UP2, Misfit Shine, and New-Lifestyles NL-1000) during two 100-step walks, one continuous 400-metre walk, and one interrupted 400-metre walk. On average, all monitors undercounted steps. Step counts from hip-worn monitors generally exhibited better reliability and validity than from wrist-worn monitors. Mobility status did not affect monitor step count errors, but interruptions to walking negatively impacted criterion validity. The hip-worn Fitbit One was the only monitor with sufficiently high test-retest reliability and criterion validity.