Don't mind your steps: Activity trackers for the assessment of physical activity in health studies

Assessing a person's physical activity is an important challenge in health studies. However, questionnaires are often inaccurate, precise monitoring devices such as high-end activity monitors are expensive and obtrusive to use, and more easily available measures such as step count are often too simple for meaningful conclusions. We therefore investigated whether data available from modern low-cost activity trackers can be used to estimate calories burnt in physical activity for cardiac prevention. We collected ground truth data from 8 users covering 157 activities on 50 days. We implemented a threshold approach for step data analysis and compared the results with the user's annotations. Compared to the commonly used IPAQ questionnaire our approach is more reliable. Our result indicates that low-cost activity trackers are a feasible tool for assessing physical activity in certain settings.