Via proprietary algorithms (Intelligent Activity Classification), accelerometer-derived information about thigh position and acceleration are used to determine body posture (i.e., sitting/lying and upright) and transition between these postures, stepping, and stepping speed (cadence), from which energy expenditure is inferred indirectly. The activPAL device (referring to all models) is a small and slim thigh-worn monitor. The thigh-mounted activPAL monitor (activPAL TM, activPA元 TM, and activPA元 TM micro PAL Technologies Ltd., Glasgow, UK) is 1 measurement device that directly measures the postural aspect of sedentary behavior. Notably, while the 2012 definition of sedentary behavior includes both energy expenditure and postural elements, 4 no field-based tool as yet directly and accurately captures both of these elements. 22 However, unlike sitting or lying, this behavior is characterised by its upright posture which elicits higher muscle contractile activity 23 with associated beneficial impacts on physiological processes such as glucose metabolism. Like sitting or lying, standing involves minimal movement and low energy expenditure. 8, 10, 18, 19, 20 However, this can lead to misclassification of low-intensity non-sedentary behaviors as sedentary behaviors. Most of the evidence on the associations of objectively assessed sedentary time and health has been derived from tools that infer sedentary time from a lack of movement. The availability of objective measurement tools with date and time-stamped information about activity is a key factor in improving our understanding of the impact of sedentary behavior and patterns of sedentary time accumulation on health. 4 It is now recognised that sedentary behavior is common (on average adults spend 46%–73% of waking hours sedentary), 5, 6, 7, 8, 9, 10 and that too much time spent sedentary may be detrimental to health both in the short term 11, 12, 13, 14 and long term. 1, 2, 3 In 2012, an expert consensus defined sedentary behavior as “any waking activity characterised by an energy expenditure ≤1.5 metabolic equivalents and a sitting or reclining posture”. Over the past decade, there has been substantial, and growing, scientific interest in sedentary behavior. Pre-data collection decisions, monitor preparation and distribution, data collection considerations, and manual and automated data processing possibilities are presented using examples from current literature and experiences from 2 research groups from the UK and Australia. It is intended that the findings and discussion points be informative for researchers who are currently using activPAL monitors or are intending to use them. We summarise key issues to consider when using the activPAL in physical activity and sedentary behavior field-based research with adult populations. The activPAL is increasingly being used within field-based research for its ability to measure sitting/lying via posture. This thigh-worn device uses accelerometer-derived information about thigh position to determine the start and end of each period spent sitting/lying, standing, and stepping, as well as stepping speed, step counts, and postural transitions. A key factor in improving our understanding of the impact of sedentary behavior (and patterns of sedentary time accumulation) on health is the use of objective measurement tools that collect date and time-stamped activity information. Research indicates that high levels of sedentary behavior (sitting or lying with low energy expenditure) are adversely associated with health.
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