Saori Braun

Extracting Objective Estimates of Sedentary Behavior from Accelerometer Data: Measurement Considerations for Surveillance and Research Applications

BACKGROUND Accelerometer-based activity monitors are widely used in research and surveillance applications for quantifying sedentary behavior (SB) and physical activity (PA). Considerable research has been done to refine methods for assessing PA, but relatively little attention has been given to operationalizing SB parameters (i.e., sedentary time and breaks) from accelerometer data - particularly in relation to health outcomes. This study investigated: (a) the accrued patterns of sedentary time and breaks; and (b) the associations of sedentary time and breaks in different bout durations with cardiovascular risk factors. METHODS Accelerometer data on 5,917 adults from the National Health Examination and Nutrition Survey (NHANES) 2003-2006 were used. Sedentary time and breaks at different bout durations (i.e., 1, 2-4, 5-9, 10-14, 15-19, 20-24, 25-29, and ≥ 30-min) were obtained using a threshold of < 100 counts per minute. Sedentary time and breaks were regressed on cardiovascular risk factors (waist circumference, triglyceride, and high-density lipoprotein cholesterol) and body mass index across bout durations. RESULTS The results revealed that the majority of sedentary time occurred within relatively short bout durations (≈ 70% and ≈ 85% for < 5-min and < 10-min, respectively). The associations of sedentary time and breaks with health outcomes varied depending on how bout time was defined. Estimates of SB parameters based on bout durations of 5 min or shorter were associated with reduced cardiovascular risk factors while durations longer than 10-min were generally associated with increased risk factors. CONCLUSIONS The present study demonstrates that the duration of sedentary bouts should be further considered when operationalizing the SB parameters from accelerometer data. The threshold of 5 minutes to define a bout is defensible, but a 10 minute threshold would provide a more conservative estimate to clearly capture the prolonged nature of sedentary behavior. Additional research is needed to determine the relative sensitivity and specificity of these thresholds.

Prediction of bone mineral density and content from measures of physical activity and sedentary behavior in younger and older females

Background Little is known regarding the extent to which physical activity (PA) and sedentary behavior (SB) influence bone mineral content (BMC) and bone mineral density (BMD) in females across the lifespan. Methods Data from 2232 females aged 12 years and older collected as part of the 2007–2008 National Health and Nutrition Examination Survey were analyzed. Categories of PA and SB were used to predict femoral and spinal BMD and BMC in four age groups (G1: 12–17; G2: 18–39; G3: 40–64; G4: ≥ 65 years). Self-reported PA categories included sufficient moderate-to-vigorous recreational PA (S-MVRPA) and insufficient MVRPA (I-MVRPA). Results G1 females who accumulated S-MVRPA displayed greater femoral and spinal BMC and BMD compared to G1 females who displayed I-MVRPA. For G4 females, higher levels of SB were associated with lower femoral BMC and BMD. Conclusions These findings highlight the importance of engaging in sufficient moderate-to-vigorous physical activity during adolescence and reducing sedentary behavior in older adults to improve bone health in females.

Sedentary Behavior, Physical Activity, and Bone Health in Postmenopausal Women

The purpose of this study was to determine if bone health at the femoral neck (FN) and lumbar spine (LS) can be predicted from objectively-measured sedentary behavior and physical activity data in postmenopausal women. Waist-mounted ActiGraph GT1M and GT3X devices were used to quantify levels of sedentary and moderate-to-vigorous intensity behavior during a 7-day period in 44 older females. Bone health (normal and osteopenia/osteoporosis) of FN and LS was derived from T scores generated using dual energy x-ray absorptiometry. Binomial logistic regression analysis indicated that sedentary time and number of breaks in sedentary behavior were significant predictors of osteopenia/osteoporosis at the FN, but not at the LS. Adherence to physical activity guidelines was not a significant predictor of bone health at the FN or LS. Our findings suggest that more frequent interruptions in sedentary behavior are associated with improved bone health in postmenopausal women.

Reliably estimating ambulatory activity in youth with arthrogryposis

Abstract Purpose: Quantification of the physical activity levels using pedometers and accelerometers in children and adolescents with mobility limitations has recently allowed researchers and practitioners to track real-life outcomes of new interventions in this particular population. Questions remain concerning the reliability of ambulatory activity monitoring in functionally challenged youth. The purpose of the analysis, therefore, was to document the minimal number of days required to reliably estimate ambulatory activity levels in children with arthrogryposis. Methods: Thirteen boys and girls with arthrogryposis (average age 10.9 years) completed stepping activity monitoring using a two-dimensional accelerometer over a period of up to 15 consecutive days. Generalizability theory was applied to identify sources of variance in daily step counts (generalizability study, G study) and to determine the number of days necessary to obtain a reliable coefficient of ≥0.80 (decision study, D study). Results: G study results showed that intra-individual variability was larger (58.4% of total variance) than inter-individual variability (28.7% of total variance). D study indicated that 9 days of monitoring was required to reach a stable measure of ambulatory activity. Conclusions: Due to relatively greater variability in step counts across days of the week, a longer monitoring period was required for youth with arthrogryposis. Implication for Rehabilitation Large proportion of variance in daily step counts was attributable to unidentifiable sources of variance, suggesting further exploration of factors that influence on the walking activity in youth with arthrogryposis. Step activity monitoring of youth with arthrogryposis should occur over a 9-day period to reliably capture their habitual level of ambulation. Rehabilitation programs aimed to promote increased stepping in youth with arthrogryposis which can utilize the findings of the present study to appropriately track their effectiveness.