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PURPOSE The objective of this study was to quantify age-related changes in accelerometer-derived day-level physical activity and sedentary behavior pattern metrics (i.e., number, length, and temporal dispersion of bouts and breaks) across 3 yr of middle childhood. Differences by child sex and weekend versus weekday were examined. METHOD Children (N = 169, 54% female, 56% Hispanic; 8-12 yr old at enrollment) participated in a longitudinal study with six assessments across 3 yr. Day-level moderate-to-vigorous physical activity (MVPA; i.e., total minutes, number of short (

Purpose: Rising rates of physical inactivity and obesity in the United States highlight the critical need to identify contexts and settings that are conducive to the promotion of recreational physical activity. The current study investigated whether the intensity and duration of sports and exercise bouts differ across physical and social environments as reported in a nationally representative time use survey of U.S. adults. Methods: From the American Time Use Survey (years 2003-2006), adult participants (ages >=21 yr) who reported at least one bout of sports or exercise on the previous day were selected (N = 7700). For each exercise bout, respondents reported the activity type, its duration (in minutes), its location (e.g., outdoors, home, work, health club/gym), and with whom it occurred (e.g., alone, family members, coworkers, friends/acquaintances). Sample-weighted logistic and linear regression analyses examined differences in intensity expressed as METs (moderate, 3.0-6.0 METs; vigorous, >6.0 METs) and in duration of exercise bouts across environments. Results: Vigorous-intensity exercise was more likely when the bout occurred alone as compared with other social situations (P values < 0.001) and when at a gym/health club and at home as compared with outdoors (P values < 0.001). For both moderate and vigorous activities, exercise bouts were shorter when exercising alone versus with family members, friends/acquaintances, or multiple categories (P values < 0.001). Mean duration of exercise bouts was greater when exercising outdoors than when exercising at home, work, or at gym/health club (P values < 0.001). Conclusions: Nationally representative time use data for U.S. adults suggest that the intensity and duration of exercise bouts are differentially affected by social contexts and physical settings.

PURPOSE: Physical inactivity is deleterious to health, but it has been difficult to determine the extent to which these effects are attributable to abnormal body composition or to factors related to physical activity alone. To begin to gauge independent effects of physical activity on health risk, we matched by BMI two groups of normal-weight adolescent females, one physically active (all participants in high school sports), and one sedentary. METHODS: Thirty-seven sedentary and 37 physically active adolescent females (mean 15.5 yr) were matched for age and BMI percentile (mean = 58.8). Comparisons included fitness, body composition and bone mineralization (by DEXA), circulating inflammatory cytokines, growth factors, bone-turnover markers, leptin, and adiponectin. RESULTS: Compared with the normal-weight sedentary girls, active girls had significantly (P < 0.05) higher fitness level (peak VO2 35.5 +/- 5.2 vs 24.4 +/- 4.1 mL.kg(-1).min(-1)), lean body mass (43.2 +/- 4.4 vs 38.7 +/- 3.6 kg), bone mineralization (spinal BMD z-scores 0.04 +/- 0.88 vs -0.41 +/- 0.85), and lower percent body fat (25.4 +/- 04.6 vs 29.7 +/- 03.7%). Additionally, active girls had lower inflammatory cytokines levels (e.g., TNF-alpha 1.7 +/- 1.3 vs 2.6 +/- 2.2 pg.mL(-1)), and leptin (17.4 +/- 11.2 vs 24.7 +/- 14.7 ng.mL(-1)), and higher bone-turnover markers (e.g. osteocalcin 12.6 +/- 7.6 vs 7.8 +/- 3.0 U.L(-1)), IGFBP-3 (6416 +/- 21280 vs 4247 +/- 1082 ng.mL(-1)), and adiponectin levels (11919 +/- 3935 vs 9305 +/- 2843 ng.mL(-1)). CONCLUSION: The normal-weight, physically active group was fitter and had greater lean body mass, stronger bones, and lower levels of inflammatory markers than did the normal-weight, sedentary group. In adolescent girls, the choice of a lifestyle involving high school sports is characterized by a circulating mediator and body composition pattern that, if sustained, is associated with generally lower long-term risk of cardiovascular disease and osteoporosis.