We evaluated anthropometric and performance measures which best predict bone mineral density (BMD) in 54 adolescent girls (14.6��0.5y; 22.7��14.0 months past menarche). BMD for the whole body, femoral neck, greater trochanter, lumbar spine (L2-L4), and mid-femoral shaft was assessed using dual-energy x-ray absorptiometry (DXA) (Hologic QDR 1000/W). Whole body lean mass and fat mass were derived from the whole body scan. Knee extensor strength and leg power were assessed by isokinetic dynamometry and the Wingate Anaerobic Power Test, respectively. Using simple regression, lean mass was significantly correlated with BMD at all bone sites r=.45-.77; p<0.001), and was more highly correlated with BMD at all sites than was body weight. Maximum leg power was also associated with bone mass at all sites (r=.41-.67; p<0.001) while leg strength correlated significantly with all sites (r=.41-.53; p<0.001) except the lumbar spine. Stepwise regression analyses revealed that 59% of the variance in whole body BMD was predicted by lean mass alone. No other variables, including fat mass, height, months past menarche, leg power, or leg strength, contributed additionally to the regression model. Similarly, lean mass was the only predictor of lumbar spine and femoral shaft BMD (R��=.25, R��=.37, respectively), while femoral neck and trochanteric BMD were best predicted by leg power (R��=.38, R��=.36, respectively). In this group of adolescent girls, lean body mass and leg power independently predicted bone mineral density of the whole body, lumbar spine, femoral shaft, and hip, which may suggest an important role for muscle mass development during growth to maximize peak bone density. / Graduation date: 1997

Thesis (M. Sc.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 85-113).

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 165-178).

Thesis (Ph. D.)--University of North Texas, Aug., 2007. / Title from title page display. Includes bibliographical references.

Thesis (M.S.)--Wake Forest University. Dept. of Health and Exercise Science, 2002. / Vita. Includes bibliographical references (leaves 54-63).

Thesis (Ph.D) - University of Queensland, 2006. / Includes bibliography.

Leung, Fung Lin Elean. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 128-157). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Motivations: Socio-economic status (SES) is a major source of health disparities. Those who lived in resource-deficient social and physical environments and with low individual income have been found to be at increased risk of physical inactivity. In Hong Kong there is virtually no research on the effect of SES on adolescent physical activity (PA). It is therefore important to explore the SES differentials in PA among Hong Kong adolescents and identify the mechanisms underlying such differentials. It is also important to examine the extent to which SES acts as a moderator and mediator of associations between various potential determinants of adolescent PA. Methods: A hundred eighty-one adolescents aged 12-18 were recruited in the study. This study applied an ecological framework to study the SES effects on adolescents’ PA participation. Physical activity was measured both objectively using accelerometers and subjectively using self-reports. Individual, social and school environment factors were assessed by validated self-report measures. Neighborhood built environmental factors were assessed using Geographic Information Systems (GIS) data. Individual-level SES was based on parents’ report of monthly household income, while area-level SES was based on census data on median household income of selected study neighborhoods. Generalized linear models with robust standard errors were used to assess associations of individual, social and environmental factors with adolescents’ PA. They were also used to assess the moderating of SES and mediators of SES-PA relationships. Results: The results supported the hypothesis that individual, social and environmental factors would all contribute to the explanation of adolescents’ PA. Moderation analyses showed that the PA level of adolescents living in low SES areas might have been negatively affected by the presence of steep streets in the neighborhood environment and the lack of sports facilities. These effects were not observed in adolescents living in high SES areas. In contrast, only adolescents living in high-SES areas showed positive associations of school-based social support and school PA-related environment with PA. Mediation analyses showed that SES differences in adolescents PA participation could be explained by social support from family and access to sports/recreational facilities in/around the school. Significance: The current findings would imply that environmental interventions at the neighborhood level might benefit low-SES groups of adolescents as they seem to be more influenced by aspects of the neighborhood environment. By contrast, high-SES adolescents might be more reactive to school-based environmental interventions. To narrow the SES gap in PA participation among Hong Kong adolescents, interventions should encourage low-SES families to provide more support to their children by widening the available range of opportunities for PA, encouraging their children to participate in PA, and acting as role models. The findings from this study also suggest that the provision of more PA facilities in/around school neighborhood in low-SES areas could contribute to increasing PA participation among the adolescent population of such areas and, thus, narrow the gap between high- and low-SES groups of adolescents. / published_or_final_version / Human Performance / Master / Master of Philosophy

Graduation date: 2005

<p>Associated with physical inactivity and obesity are numerous other health risks which have become a major health concern. A steady decrease in the levels of physical activity during childhood and adolescents have been noted in various parts of the world. The picture of low physical activity levels in developed countries is no different in developing countries. Children spend the majority of their day at school therefore a school setting is ideal to conduct physical activity intervention studies The primary aim of this study was to measure the effect of an intervention programme on the physical activity participation levels among school going children and adolescents. The study was carried out at an urban independent Catholic school. The sample, which was conveniently selected, which included 100 learners from grade 5 to 7 with parental consent. A quantitative approach using a quasi-experimental design was used in this study. Baseline data included levels of physical activity participation, Body Mass Index (BMI), hip-waist ratio, and socio-demographic variables. Physical activity was assessed with the Modifiable Activity Questionnaire for Adolescents. The Promoting Lifestyle activity for Youth (PLAY) programme was implemented at the school. This process-oriented programme shifts the focus from fitness toward regular participation in daily physical activity, and it is not intended to replace a comprehensive physical education programme.</p>