Measurement issues and poor adjustments for physical activity and sleep undermine sedentary behaviour research—the focus should shift to the balance between sleep, sedentary behaviour, standing and activity

This paper critically appraised 54 recent studies linking sedentary behaviour (SB) and health, specifically regarding their assessment of SB and adjustments for physical activity (PA) and sleep. Almost 90% of the studies collected SB data using self-reports and 59% of these measures had not been previously validated. The majority of studies did not adjust for total PA or for both light-intensity PA (LIPA) and moderate-tovigorous-intensity PA (MVPA), and a large number of studies did not adjust for all domains of PA. It may, therefore, be that these adjustments were not thorough enough to allow for sound conclusions about the independent associations between SB and health outcomes. Sleep time is also likely to act as a confounding variable in associations between SB and health outcomes. Despite that, only three reviewed studies adjusted their analyses for sleep duration. Evidence presented here casts doubt upon the conclusions about independent associations between SB and health outcomes. Given the facts that: 1) the proportions of time allotted to sleep, SB, standing, LIPA and MVPA are perfectly collinear, 2) all these behaviours may be associated with health, and 3) mutual adjustments between all these variables are needed if their independent contributions to health are to be determined, it seems that investigating the balance between times spent in these behaviours is the next logical step in epidemiological research. This paper, therefore, proposes the Activity Balance Model (AB model); a new theoretical framework for investigating associations of sleep duration, SB, standing, LIPA and MVPA with health outcomes.