Physical activity and sedentary behaviour in youth have been reported to vary by sex, age, weight status and country. However, supporting data are often self-reported and/or do not encompass a wide range of ages or geographical locations. This study aimed to describe objectively-measured physical activity and sedentary time patterns in youth. The International Children’s Accelerometry Database (ICAD) consists of ActiGraph accelerometer data from 20 studies in ten countries, processed using common data reduction procedures. Analyses were conducted on 27,637 participants (2.8–18.4 years) who provided at least three days of valid accelerometer data. Linear regression was used to examine associations between age, sex, weight status, country and physical activity outcomes. Boys were less sedentary and more active than girls at all ages. After 5 years of age there was an average cross-sectional decrease of 4.2 % in total physical activity with each additional year of age, due mainly to lower levels of light-intensity physical activity and greater time spent sedentary. Physical activity did not differ by weight status in the youngest children, but from age seven onwards, overweight/obese participants were less active than their normal weight counterparts. Physical activity varied between samples from different countries, with a 15–20 % difference between the highest and lowest countries at age 9–10 and a 26–28 % difference at age 12–13. Physical activity differed between samples from different countries, but the associations between demographic characteristics and physical activity were consistently observed. Further research is needed to explore environmental and sociocultural explanations for these differences.

This study examined the psychometric properties of two versions of a commonly used physical activity 7-d self-report, the Physical Activity Questionnaire for Older Children (PAQ-C) and Physical Activity Questionnaire for Adolescents (PAQ-A). We longitudinally examined the internal consistency, stability, and situational effects of the PAQ-C and PAQ-A in a cohort of children (N = 210) at ages 11 and 13 yr. Statistical analysis included factor loading and standardized Cronbach coefficient alphas. We cross-sectionally examined concurrent validity of the PAQ-A in a subsample of our cohort (N = 49) at age 13 by comparing it with concurrently measured physical activity using an activity monitor (Actigraph). Spearman correlation coefficients were used for this analysis. Standardized Cronbach alphas ranged from 0.72 to 0.88. A subsample analysis suggested that completing the questionnaires during the summer months slightly reduced the standardized alpha for the PAQ-C, but not the PAQ-A. Associations between the PAQ-A (revised) summary score and activity monitor variables were rho = 0.56 for total PA and rho = 0.63 for moderate through vigorous activity (P < 0.05). Associations between individual PAQ-A questions and activity monitor variables for the same time frame ranged from rho = 0.41 to 0.62 (P < 0.05). The PAQ-C and PAQ-A show good internal consistency. The PAQ-A has acceptable validity.

JANZ, K. F., J. D. DAWSON, and L. T. MAHONEY. Tracking physical fitness and physical activity from childhood to adolescence: the Muscatine study. Med. Sci. Sports Exerc., Vol. 32, No. 7, pp. 1250–1257, 2000. Physical fitness and physical activity tracking data enhance our understanding as to when children settle into their long-term exercise and fitness patterns and, therefore, provide insight as to when programs focusing on preventing sedentary adults behaviors should be initiated. In this paper, the tracking of physical fitness and physical activity was examined in a 5-yr population-based study of children and adolescents in Muscatine, IA. Study subjects (N = 126) were pre- or early-pubescent at baseline (mean age boys 10.8 yr and girls 10.3 yr). Physical fitness was measured using direct determination of oxygen uptake and maximal voluntary isometric contraction while physical activity was assessed via questionnaire. Boys classified as sedentary based on initial measurements of TV viewing and video game playing were 2.2 times more likely than their peers to also be classified as sedentary at follow-up. Tracking of most physical fitness and physical activity variables was moderate to high, indicating some predictability of early measurements for later values. Sedentary behavior tracked better in boys, whereas vigorous activity tended to track better in girls. These observations suggest that preventive efforts focused on maintaining physical fitness and physical activity through puberty will have favorable health benefits in later years.

Objectives. Physical activity has a beneficial effect on bone development in circumpubertal children, although its effect on younger children is uncertain. In this cross-sectional study, we examined associations between physical activity and bone measures in 368 preschool children (mean age: 5.2 years, range: 4–6 years). Design. Physical activity was measured using 4-day accelerometry readings, parental report of children9s usual physical activity, and parental report of children9s hours of daily television viewing. Total body and site-specific bone mineral content and area bone mineral density (BMD) were measured by dual energy radiograph absorptiometry. Results. After adjustment for age and body size, accelerometry measures of physical activity and parental report of usual physical activity were consistently and positively associated with bone mineral content and BMD in both boys and girls (r = 0.15–0.28). Television viewing was inversely associated with hip BMD in girls (r = −0.15). The proportion of variance in bone measures explained by physical activity in linear regression models ranged fromr² = 1.5% to 9.0%. In all of these models except total body BMD, at least 1 and often several of the physical activity variables entered as independent predictors. Activity variables most likely to enter the regression models were vigorous physical activity (as determined by accelerometry) and parental ranking of child9s usual physical activity. Conclusions. Findings indicate that there are statistically significant and, perhaps important, associations between physical activity and bone measures during early childhood, well ahead of the onset of peak bone mass. This would suggest that intervention strategies to increase physical activity in young children could contribute to optimal bone development.