Children without siblings (only children) have higher rates of obesity than children with siblings. Childhood obesity may be prevented by minimising sedentary behaviour and accumulating sufficient physical activity in young children. A growing number of articles have examined the influence of siblings on physical activity and sedentary behaviour, yet these articles have not been synthesised. Objective To synthesise literature and describe the influence of siblings on objectively measured physical activity and sedentary behaviour of children (ages 2–18 years). Design Outcomes were analysed in a systematic review and meta-analysis. Data sources PubMed, EMBASE, Web of Science and Medline OVID were searched for articles related to siblings, physical activity, sedentary behaviour and obesity outcomes from 1947 to March 2018. Eligibility criteria Articles that evaluated sibling status on physical activity objectively measured by accelerometer or pedometer were included. Results Nineteen articles, representing 17 independent datasets, were included in the review. Nine were included in the quantitative analysis. Pooled data from nine articles indicated children with siblings had higher moderate-to-vigorous physical activity (MVPA) relative to only children, with a potential dose response for higher number of children in household and higher MVPA (Mean Difference=3.13, 95% CI 1.90 to 4.35, p=0.001). Findings were mixed for the influence of siblings on sedentary behaviour and light physical activity. Summary/Conclusion Children with siblings had healthier physical activity patterns, as measured by accelerometer or pedometer, than did only children. Suggested mechanisms include peer modelling, encouraging active transport and sports participation, opportunity for playmate and serving as additional caregivers. Trial registration number CRD42017055463.

Purpose.: Descriptive physical activity epidemiology of the U.S. population is critical for program development and resource allocation. The purpose of this project was to describe step-defined categories (as measured by accelerometer) of U.S. adults and to determine predictors of sedentary classification (<5000 steps/d). Design.: The National Health and Nutrition Examination Survey (NHANES) is an annual, nationally representative survey used to determine the health status of the U. S. populace. Setting.: In-home interviews and physical examination components of NHANES. Participants.: Overall, 4372 eligible adults wore accelerometers in the 2005–2006 NHANES; 628 were excluded, which yielded 3744 adults (of which 46.8% were men). Measures.: Steps per day; body mass index (BMI); demographic, household and behavioral variables. Analysis.: Means and frequencies were calculated. Logistic regression was utilized to determine predictors of sedentary classification. Results.: Overall, 36.1% were sedentary (i.e., <5000 steps/d); 47.6% were low to somewhat active (5000–9999 steps/d); 16.3% were active to highly active (≥ 10,000 steps/d). Advancing age (odds ratio [OR], 1.95; confidence intervals [CIs], 1.78, 2.13), higher BMI (OR, 1.40; CIs, 1.23, 1.59), female sex (OR, 1.86; CIs, 1.46, 2.36), African-American versus European-American ethnicity (OR, 1.36; CIs, 1.13, 1.65), household income versus ≥ $45,000 (<$25,000: OR, 1.94; CIs, 1.40, 2.69; $25,000–$44,000: OR, 1.51; CIs, 1.23, 1.85), and current versus never smoker (OR, 1.53; CIs, 1.26, 1.86) variables had higher odds of sedentary classification. Usual daily occupational/domestic physical activity categories of standing/walking (OR, .51; CIs, .38, .69); lifting/climbing (OR, .26; CIs, .17, .38); and heavy loads/labor (OR, .16; CIs, .10, .26) had lower odds of sedentary classification than sitting. Conclusions.: Over one-third of the U.S. population was classified as sedentary by accelerometer-determined steps per day, and several characteristics predicted sedentary classification.