Participation in vigorous sports, not moderate sports, is positively associated with cardiorespiratory fitness among adolescent girls.

BACKGROUND: There is controversy regarding whether moderately-intense sports can improve physical fitness, which declines throughout adolescence among girls. The objective was to estimate the association between moderate and vigorous sports participation and cardiorespiratory fitness in a racially diverse sample of adolescent girls. METHODS: Cardiorespiratory fitness was measured using a modified physical work capacity test in 1029 eighth-grade girls participating in the Trial of Activity for Adolescent Girls. Girls reported sports in which they participated in the last year on an organized activity questionnaire. Using general linear mixed models, the study regressed absolute and relative fitness on the number of vigorous and moderate sports in which girls participated, race/ethnicity, age, treatment group, fat mass, fat-free mass, and an interaction between race and fat-free mass. RESULTS: The number of vigorous sports in which girls participated was positively associated with absolute fitness (ß = 10.20, P = .04) and relative fitness (ß = 0.17, P = .04). Associations were reduced, but not eliminated, after controlling for MET-weighted MVPA. Participation in moderate sports was not associated with either fitness measure. CONCLUSIONS: Vigorous sports participation is positively associated with cardiorespiratory fitness. Future longitudinal research should analyze whether promoting vigorous sports at an early age can prevent age-related declines in cardiorespiratory fitness among adolescent girls.

A longitudinal study of sedentary behavior and overweight in adolescent girls.

The aim of this study is to examine sedentary and light activity in relation to overweight in adolescent girls. Adolescent girls were randomly recruited from 36 schools participating in the Trial of Activity for Adolescent Girls (TAAG). Assessments included age, ethnicity, socioeconomic status, and body composition estimated from weight, height, and triceps skinfold. Sedentary and light activity was measured for 6 days using accelerometry in 6th and in 8th grade among two randomly sampled cross-sections of girls. Sedentary activity increased from the 6th to 8th grade by 51.5 min/day. In the 8th grade, a significantly higher number of hours in sedentary activity for each of the 6-days of measurement were evident with higher tertiles of percent body fat (30-35%, >35% fat) (P < 0.05), but not across all increasing tertiles of BMI (5th to 85th, 85th to 95th, and >95th percentiles). The increase in sedentary activity was observed on weekdays, but not on weekends for percent body fat tertiles. In the cohort of girls measured in both 6th and 8th grades, the mean cross-sectional coefficient estimates were significant for percent body fat, but not BMI for sedentary and light activities. Adolescent girls from the 6th to 8th grade are shifting their time from light to more sedentary activity as measured by accelerometers. In addition, the increase in sedentary activity is not associated with an adverse effect on BMI or percent body fat. The eventual impact of this shift to a more sedentary lifestyle on body composition and other outcomes needs to be evaluated further.