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Purpose: To examine whether there are differences between demographic, behavioral, and biological variables for those with invalid accelerometry data (IAD) and those with valid accelerometry data (VAD)., Design: Cross-sectional., Setting: Data from 2003-2006 National Health and Nutrition Examination Survey (NHANES) were used., Subjects: Participants included 1,315 children (i.e., 6-11 years) with VAD and 534 children with IAD and 1,859 adolescents (i.e., 12-17 years) with VAD and 1,057 with IAD., Measures: Physical activity (PA) was measured using an accelerometer, with questionnaires used to assess demographic and behavioral variables and biological parameters assessed from a blood sample., Analysis: Wald and design-based likelihood ratio tests and logistic regression were used to assess differences between those subjects with IAD and those with VAD., Results: After adjustments, overweight children, compared to normal weight children, were 1.6 (odds ratio [OR] = 1.67; 95% confidence interval [CI]: 1.22-2.29) times more likely to have IAD. After adjustments, and as an example, adolescents engaging in 4 or more hours of computer use per day, compared to no computer use, were 2.6 (OR = 2.6; 95% CI: 1.38-5.18) times more likely to have IAD., Conclusion: Excluding youth with IAD may introduce bias, limit generalizability, and ultimately underestimate the association between PA and health outcomes. Future research is needed to identify reasons for poor monitoring compliance.

The association between physical activity (PA) and C-reactive protein (CRP) is inconsistent, with nearly all studies using self-report measures of PA. The purpose of this study was to examine the association between objectively measured PA and CRP in US adults and children. Adults ( N=2912) and children ( N=1643) with valid accelerometer data and CRP data were included in the analyses. Logistic regression analysis was used to assess the odds of meeting PA guidelines across CRP quartiles for children and among adults with low, average, and high CRP levels. For adults, after adjustments for age, gender, race, body mass index, smoking, diabetes, and high-density lipoprotein cholesterol (HDL-C), compared with those with low CRP levels, odds ratios were 0.59 (CI=0.45-0.77) and 0.46 (CI=0.28-0.76) for participants with average and high CRP levels, respectively. For children, after adjustments for age, gender, race, weight status, and HDL-C, compared with those in CRP quartile 1, odds ratios were 0.96 (CI=0.5-1.84), 1.23 (CI=0.71-2.12), and 0.79 (CI=0.33-1.88) for participants in quartiles 2, 3, and 4, respectively. Objectively measured PA is inversely associated with CRP in adults, with PA not related to CRP in children. [ABSTRACT FROM AUTHOR]