BACKGROUND: Step-based metrics, including steps/day and cadence (steps/min), are well established in the physical activity literature. However, there remains a need for robust criterion validation of step-counting wearable technologies across a wide range of ambulatory movements. Validation studies have typically examined device accuracy during rhythmic treadmill or overground walking, with few studies examining step-count accuracy during simulated activities of daily living (SADL). PURPOSE: To determine the step-count criterion validity of wearable devices during SADLs. METHODS: Participants (N = 260, 52.7±18.9 years, BMI 25.6±3.7 kg/m2, 50% women) from the CADENCE-Adults study, completed a series of laboratory-based SADLs, including folding laundry, vacuuming, stair stepping, and preferred pace overground walking. Participants wore devices on their waist (Yamax Digiwalker SW200 [SW200], New Lifestyles NL1000 [NL], ActiGraph GT9X [AG] and ActiCal [AC]), thigh (activPal [AP]), and ankle (StepWatch [SW]). The criterion measure was directly observed hand-counted steps (both in real-time and verified using video recording). Equivalence testing plots were generated to assess the criterion validity of each device. Unlike traditional null hypothesis testing, which seeks to determine whether there were any statistical differences between devices, equivalence testing evaluates agreement between the criterion and test device. The equivalence zone was set at ±0.2 SD of the criterion step count for each SADL. Devices were deemed equivalent to the criterion when their mean error and the 95% CI fell within the equivalence zone. RESULTS: On average, devices tended to underestimate (-4, -31, -28, -6 steps/min) for folding laundry, vacuuming, stair stepping, and overground walking, respectively. No devices fell inside the equivalence zone for folding laundry, vacuuming, and stair stepping. For preferred pace overground walking, only the SW and AP fell within the equivalence zone. CONCLUSIONS: No device performed well across the full range of activities; however, the SW and AP were deemed equivalent during preferred pace overground walking. Device manufacturers should aim to refine step algorithms to improve step-count accuracy across a wider range of ambulatory activities. FUNDING: NIH-NIA-5R01AG049024

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