Purpose: This study explored definitions of sedentary behavior and examined the relationship between sitting time and physical inactivity using the sitting items from the International Physical Activity Questionnaire (IPAQ). Methods: Participants (N = 289, 44.6% male, mean age = 35.93) from 3 countries completed self-administered long-and short-IPAQ sitting items. Participants wore accelerometers; were classified as inactive (no leisure-time activity), insufficiently active, or meeting

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... ations; and were classified into tertiles of sitting behavior. Results: Reliability of sitting time was acceptable for men and women. Correlations between total sitting and accelerometer counts/min <100 were significant for both long (r = .33) and short (r = .34) forms. There was no agreement between tertiles of sitting and the inactivity category (kappa = .02, P = .68). Conclusion: Sedentary behavior should be explicitly measured in population surveillance and research instead of being defined by lack of physical activity.