Individual Physical Activity
MEASURES REGISTRY USER GUIDE
Supplemental Considerations for Evaluating Sedentary Behavior
The health and behavioral consequences of sedentary behavior has generated considerable public health interest. Research is still in its infancy, but consensus has emerged that sedentary behavior is distinct from physical activity behavior in youth. Low levels of physical activity cannot be inferred to reflect high sedentary behavior, and high levels of physical activity cannot be assumed to reflect low sedentary behavior. Assessment strategies are also inherently different, and challenges in assessing sedentary activities have confounded efforts to better understand this behavior in youth. The Measures Registry is well positioned to facilitate selection of effective sedentary behavior measures to guide future research. This section will provide brief summaries of issues associated with the evaluation of sedentary behavior using both monitor- and report-based measures. More detail is available elsewhere.86-87
Background on Sedentary Behavior
Early concerns about sedentary behavior in youth stemmed from studies showing that excess television (TV) viewing was a likely contributor to the epidemic of childhood obesity. Further interest was sparked by studies in adults showing that sedentary behavior may influence health risks independent of physical activity behavior.88 Research to date, however, has not supported the independence of sedentary behavior as a health risk in youth when physical activity is taken into account. The health implications of sedentary behavior in youth warrant further evaluation, but there is no doubt that it is an important behavioral target for intervention and a priority for family, school, and community programming.
Assessments of Sedentary Behavior
The focus of this Guide has been on evaluating physical activity behavior, but evaluating sedentary behavior has unique considerations. A complicating factor in sedentary behavior research is the ever-changing nature of technology in society. Common forms of physical activity have remained relatively consistent over the years, but this is not the case with sedentary behavior. Public health recommendations for sedentary behavior have focused on excess TV viewing and computer games,89 but it is likely that youth now spend more time on their smartphones or on handheld or tablet devices than watching or using TV. The blurring of technology makes it difficult to characterize sedentary behavior but another challenge is that time spent in sedentary behavior may include desirable behaviors, such as doing homework, reading, or playing music. Thus, it is important to distinguish discretionary or recreational sedentary behavior from required or desired forms of sedentary behavior. Device-based measures that provide objective information on movement are being used to assess sedentary behavior, but certain caveats and assumptions must be considered when interpreting the data. Research has demonstrated differences in the nature and patterns of findings depending on how sedentary behavior is assessed, so it is important to understand the advantages and disadvantages of each approach.
Quantifying Sedentary Behavior with Report-based Measures
An advantage of report-based measures is that they can provide information about the type and context of sedentary behavior, but a disadvantage is the difficulty in quantifying sedentary behavior due to recall bias. Guidelines have been proposed to assist researchers in choosing appropriate self-report instruments for evaluating sedentary behavior.2 Comprehensive systematic reviews have also provided specific insights on the validity and reliability of self-report measures for youth.87,90 The reviews have demonstrated clear limitations with standard time-use methods. However, few self-report tools have been developed specifically to assess youth sedentary behaviors.
Quantifying Sedentary Behavior with Monitor-based Measures
Monitor-based measures are designed to evaluate movement so it is somewhat paradoxical to operationalize “lack of movement” as sedentary behavior, especially considering that physical activity and sedentary behavior are thought to be independent of each other. A key advantage for sedentary behavior work is that monitor-based measures can provide detailed information about breaks and bouts of sedentary behavior. However, they cannot distinguish specific types of sedentary behavior or provide contextual information about sedentary behavior. The activPAL is a unique example of a monitor-based measure that can differentiate sitting from other postures with a high degree of precision and therefore adds great value for measuring sedentary behavior. However, the majority of work has used the Actigraph monitor and support is strong for using a threshold of 100 counts/minute for detecting sedentary behavior at the hip.u,91 Even though this threshold was not empirically derived, the assumption is that the accumulation of little or no movement over a certain time interval could only occur if a person was sedentary. Thresholds do not hold for other monitors, and recent evidence demonstrates that unique thresholds are needed for monitors worn at the wrist.91 This makes conceptual sense because arms and hands can be performing small movements even when a person is sedentary.
u It is important to acknowledge that debate continues about the most appropriate threshold for hip-worn monitors but studies have used the value of 100 and this threshold has been well supported. However, it does not hold for other monitors or other positions.