The Feasibility of Reducing and Measuring Sedentary Time among Overweight, Non-Exercising Office Workers

This study examined the feasibility of reducing free-living sedentary time (ST) and the convergent validity of various tools to measure ST. Twenty overweight/obese participants wore the activPAL (AP) (criterion measure) and ActiGraph (AG; 100 and 150 count/minute cut-points) for a 7-day baseline period. Next, they received a simple intervention targeting free-living ST reductions (7-day intervention period). ST was measured using two questionnaires following each period. ST significantly decreased from 67% of wear time (baseline period) to 62.7% of wear time (intervention period) according to AP (n = 14, P < 0.01). No other measurement tool detected a reduction in ST. The AG measures were more accurate (lower bias) and more precise (smaller confidence intervals) than the questionnaires. Participants reduced ST by ~5%, which is equivalent to a 48_min reduction over a 16-hour waking day. These data describe ST measurement properties from wearable monitors and self-report tools to inform sample-size estimates for future ST interventions

Validation of a Previous-Day Recall Measure of Active and Sedentary Behaviors

Purpose—A previous-day recall (PDR) may be a less error prone alternative to traditional questionnaire-based estimates of physical activity and sedentary behavior (e.g., past year), but validity of the method is not established. We evaluated the validity of an interviewer administered PDR in adolescents (12–17 years) and adults (18–71 years). Methods—In a 7-day study, participants completed three PDRs, wore two activity monitors, and completed measures of social desirability and body mass index (BMI). PDR measures of active and sedentary time was contrasted against an accelerometer (ActiGraph) by comparing both to a valid reference measure (activPAL) using measurement error modeling and traditional validation approaches. Results—Age- and gender-specific mixed models comparing PDR to activPAL indicated: (1) a strong linear relationship between measures for sedentary (regression slope = β1=0.80 to 1.13) and active time (β1=0.64 to 1.09); (2) person-specific bias was lower than random error; and (3) correlations were high (Sedentary: r = 0.60 to 0.81; Active: r = 0.52 to 0.80). Reporting errors were not associated with BMI or social desirability. Models comparing ActiGraph to activPAL indicated: (1) a weaker linear relationship between measures for sedentary (β1=0.63 to 0.73) and active time (β1=0.61 to 0.72); (2) person-specific bias was slightly larger than random error; and (3) correlations were high (Sedentary: r = 0.68 to 0.77; Active: r = 0.57 to 0.79). Conclusions—Correlations between the PDR and activPAL were high, systematic reporting errors were low, and the validity of the PDR was comparable to the ActiGraph. PDRs may have value in studies of physical activity and health, particularly those interested in measuring the specific type, location, and purpose of activity-related behaviors