Introduction: Sedentary behavior (SB) influences health status independently of physical activity. The formal definition of SB is: "any waking behavior characterized by an energy expenditure ≤1.5 METs while in a sitting or reclining posture". However, measuring SB mostly does not include both the intensity and postural component. The aim of this study was to quantify the effect of type of operationalization of SB on total sedentary time and the pattern of SB.
Methods: 53 healthy subjects were measured 24h with a multi-sensor activity monitor that provides a valid one-second detection of body postures and movements and a calculated intensity measure. The SB outcome measures were: total sedentary time; number of sedentary bouts; mean bout length; fragmentation; and W-index. All outcomes were calculated for three types of operationalization of SB: 1) waking time in lying and sitting posture and below the sedentary intensity threshold (<0.016g comparable with Actigraph <150 counts, COMBI); 2) waking time in lying and sitting posture (POST); 3) waking time below the sedentary intensity threshold (<0.016g, INT). Outcome measures based on these three operationalizations were compared with repeated measures ANOVA.
Results: Total sedentary time was significantly different (p<0.001) between all three conditions: 505.8 (113.85)min (COMBI), 593.2 (112.09)min (POST), and 565.5 (108.54)min (INT). Significant differences were also found for other outcome measures.
Conclusion: Our study shows that type of operationalization significantly affects SB outcome measures. Therefore, if SB is defined according to the formal definition, measurements must include both the intensity and postural component.
Keywords: Accelerometry; Healthy volunteers; Measurement; Sedentary lifestyle; Validity.
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