Backgrounds: This study aimed to explore the effect on physical activity and sedentary behavior of users of wearable devices, and understand the association between physical activity and behavior. Methods: This study conducted a three-arm, randomized controlled trial for 12 weeks. Healthy adults without experience of using a wearable device were recruited and were randomly assigned to a control group with a mobile app and two experimental groups with different smart wearable devices. Data were collected through questionnaires. Results: No significant effect of group, time, or group-by-time interaction among groups for physical activity, sedentary time, or sleep quality was found. Wearing duration significantly positively predicted changes in low-intensity and total physical activity. The number of times the device was checked negatively predicted a change in sedentary time. Conclusions: The behavior of wearable device users is an essential factor for successfully increasing physical activity and decreasing sedentary time.
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