Physical inactivity is becoming an important component of the physical activity and health equation. Sedentary behavior refers to any waking activity characterized by an energy expenditure ≥ 1.5 METS and a sitting or reclining posture (1). Time spent in sedentary behavior is distinct from lack of physical activity as these are considered unique behavioral constructs that have independent relationships to various health outcomes.(2) New evidence suggests that prolonged, unbroken sitting time is related to increased risk of obesity, type 2 diabetes, and cardiovascular disease.
In public health recommendations, physical inactivity is often used to refer to a broader pattern of behavior that is marked by low levels of physical activity and/or has an excess of time spent sitting, or sedentary. In epidemiological research, the term “ physical inactivity” refers to a state in which body movement is minimized.(3) This would include sleeping, as well as, activities performed during waking hours that result in lower levels of energy expenditure. Physical inactivity that takes place during waking hours is typically referred to as sedentary behavior.(4) Understanding the roles of both physical activity and sedentary behavior in disease pathways requires methods that can accurately report low intensity activities in addition to moderate and high intensity activities. Therefore, intensity of activity can have important implications on which method of assessment is the most appropriate for a given research design. In general, measurement methods that do not adequately capture information on frequency, duration, and intensity will result in less precise or inaccurate assessments of both physical activity and sedentary behavior.
Examples of Sedentary Behaviors:
- Sitting Time
- TV viewing
- Playing video games
- Computer use
- Homework
- Commuting (Driving or Passenger)
- Reading
Similar to physical activity, sedentary behavior may be assessed using objective measures. Below are some commonly used objective measures to assess sedentary behavior:
Direct Measures:
- Accelerometers
- Accelerometers are small electronic devices worn on the hip that provide an objective record of the volume, intensity, and frequency of movement. Accelerometers have been traditionally used to measure light to vigorous intensity physical activity. More recently, accelerometers have been used to measure sedentary behavior. Sedentary behavior assessed by accelerometers is usually defined as counts less than 100 per minute.
Advances in technology, allow for newer functionality of accelerometers. Some newer models of accelerometers include inclinometers which measure body position (sitting, standing, lying).
- Inclinometers
- Inclinometers are instruments that measure posture and can distinguish between sitting, standing, and lying. Inclinometers are now being included in accelerometers and provide additional information that allows for better classification of sitting or sedentary time.
- Direct Observation
- Similar to accelerometers, direct observation has often been used to assess physical activity but is also been used to measure sedentary behavior. Direct observation is a technique by which a trained observer classifies free-living physical activity or sedentary time by objectively recording the observed behavior for a predetermined length of time. All recordings are entered into a computer or paper-and-pencil entry form. Observations typically occur in natural settings such as home or during school. Direct observation is often used in children and youth populations, but may also be used in adult populations.
With regard to sedentary behavior, direct observation either by video or by a researcher/ trained observer is considered a gold standard method for measuring screen time. However, it is important to note that direct observation is burdensome for the researcher/trained observer, time consuming, and may alter behavior of the individual(s) being observed.
References
- Sedentary Behaviour Research Network. 2012. Standardized use of the terms “sedentary” and “sedentary behaviours”. Appl Physiol Nutr Metab. 37: 540–542.
- Dunstan DW, Barr EL, Healy GN, Salmon J, Shaw JE, Balkau B et al. Television viewing time and mortality: the Australian Diabetes, Obesity and Lifestyle Study (AusDiab). Circulation 2010; 26: 384–391.
- Dietz WH. The role of lifestyle in health: the epidemiology and consequences of inactivity. Proc Nutr Soc. 1996;55(3):829-40.
- Owen N, Healy GN, Matthews CE, and Dunstan DW. Too much sitting: the population health science of sedentary behavior. Exerc Sport Sci Rev. 2010;38(3):105-13.