Preventing the ‘24-hour Babel’: the need for a consensus on a consistent terminology scheme for physical activity, sedentary behaviour and sleep

Clear, concise, and consistent. These qualities (the 3Cs) are critical for effective scientific communication. Plain language enables easy comparisons between study findings, ensures construct uniformity, and enhances communication of scientific discoveries to audiences beyond academia. Health research has a growing interest in the inter-relationships of physical activity (PA), sedentary behaviour (SB) and sleep. These behaviours occupy most of the 24-hour cycle and are associated with a plethora of health outcomes.1 Consensus statements suggest how to analyse these behaviours.2 Some PA/SB guidelines have incorporated sleep using mostly cross-sectional evidence.1 However, these consensus statements and guidelines fail to acknowledge the interactive and reciprocal relationships between PA, SB and sleep. As more scientists enter this field (figure 1), terminology is becoming inconsistent and confusing. Here, we outline the disparate vocabulary for the 24-hour cycle, and make the case for a consensus project to address how we collectively think about and refer to PA, SB and sleep using the 3Cs principle. Figure 1 PubMed search hits from 2010 to 2020 for each term for collectively defining physical activity, sedentary behaviour and sleep. Health research has a well-defined vocabulary for behaviours which occupy most of the 24-hour cycle. PA is any bodily movement which increases energy expenditure above 1.5 metabolic equivalents (METs).3 SB is any behaviour performed from a seated/lying position that requires ≤1.5 METs.4 …