Sedentary behaviour is a category of complex behaviours which are characterised by three main criteria:
Figure P.1.8 below, distinguishes sedentary behaviour from the other main behaviour categories, based on the criteria described above. The inner ring represents the main behaviour categories using energy expenditure and awake state. The outer ring provides general categories using posture. The proportion of space occupied by each behaviour in this figure is not prescriptive of the time that should be spent in these behaviours each day.
Figure P.1.8 [awaiting upload] 24-hour movement and non-movement behaviours. Source: Tremblay et al., 2017.
Some activities performed while standing may have an energy requirement of ≤1.5 METs but are not considered sedentary behaviours, as they lack the postural element of the definition.
Conversely, other activities are performed while being seated or reclined but require physical work >1.5 METs (e.g. rowing), and are hence also not classified as sedentary behaviours.
Sleeping is a distinct behaviour which is characterised by both very low energy expenditure and (usually) a lying posture but by definition not awake, allowing the brain to process experiences and restore its energy. Hence, sleep is also not considered a sedentary behaviour.
Current modernised societies cater for high levels of sedentary behaviour. High global prevalence levels have fuelled an exponential increase in research interest in this area. Evidence from observational and experimental research on the health effects of excessive levels of sedentary behaviour, have made reductions in sedentary behaviour an inherent part of recent national and international physical activity guidelines.
A wide variety of sedentary behaviour types exist (e.g. eating while sitting). TV viewing is a sedentary behaviour type that received particular attention in early stages of sedentary behaviour epidemiology. This was predominantly based on inclusion of this behaviour, then assumed to be a “proxy” measure of sedentary behaviour, in several large-scale observational cohorts a few decades ago. Since then, the focus has shifted towards a more diverse range of sedentary behaviour types, domains or overall sedentary time, measured by subjective or objective methods. Recent developments in terminology reflect this and have also provided clearer definitions; for example for different types of screen time, including sedentary versus active screen time (e.g. active computer games).
Most desk-based office work, driving or riding in a car, and watching television are examples of sedentary behaviours and can also apply to those unable to stand, such as wheelchair users. However, it should be recognized that certain population groups, such as wheelchair users or non-ambulatory individuals, unavoidably sit for long periods of time and sitting may therefore be the norm. For these populations, sedentary behaviour is best defined based on the low energy expenditure component, rather than the postural component (e.g. moving in a power chair or being pushed in a wheelchair).
As indicated above, sedentary behaviours can also be distinguished more broadly by the domain (setting or context) in which they occur, such as sitting at work, for travel, in leisure time or at home.
Similar to physical activity, sedentary behaviours can also be described by their frequency, duration, timing and intensity (e.g. below certain acceleration thresholds on an accelerometer) and variability. The manner in which sedentary behaviour is accumulated throughout the day or week, i.e. the bout duration and/or frequency, or the time of day at which sedentary bouts occur, is referred to as the sedentary behaviour pattern. Observational and experimental research suggests that specific patterns of sedentary time (i.e. whether it is undertaken in relatively more prolonged or shorter bout durations) may be differentially associated with intermediate cardio-metabolic risk factors, chronic disease and premature mortality.
Sedentary behaviours are considered conceptually distinct from physical inactivity, with the latter referring to insufficient amounts of moderate-to-vigorous physical activity (MVPA) to meet current physical activity recommendations. From a measurement perspective, MVPA and sedentary behaviour are often poorly correlated at the group level, and high levels of daily sedentary behaviour and MVPA can easily co-exist in the same individual. Put simply, it is possible for a person to meet or exceed the public health guidelines for MVPA, and yet also spend most waking hours sedentary, potentially increasing one’s health risk.
Figure P.1.9 Four different and plausible daily activity profiles. Profile D illustrates the potential for high levels of sedentary behaviour and moderate-to-vigorous physical activity (MVPA) to co-exist.