Teses e Dissertações

• Teses
• Dissertações

ARTIGOS

 

1- A methodological model for collecting high-quality data on physical activity in developing settings - The experience of the 1993 Pelotas (Brazil) Birth Cohort Study

 

ABSTRACT

 

Background

Prospective studies on physical activity (PA), diet, and body composition in adolescents are lacking, particularly outside high-income countries. The aims of this paper were to describe the methods used for assessing these variables in the 1993 Pelotas (Brazil) Birth Cohort, and to discuss the fieldwork challenges faced and alternatives to overcome them.

 

Methods

 

In 2006-7 a sub-sample of the 1993 Pelotas cohort was revisited. PA was estimated using questionnaires, a combined heart rate and motion sensor (Actiheart), and the Actigraph GT1M accelerometer. Diet was investigated by questionnaire. Total body water was determined by stable isotopes. Thirty individuals had their total energy expenditure assessed by double labeled water. All data were collected at participants’ home.

 

Results

 

The logistics of the fieldwork and the difficulties in undertaking the study and alternatives to overcome them are presented. Preliminary analyses show that 511 individuals were traced (response rate = 90.0%). Compliance of both adolescents and their families for the motion sensors and body composition measurements was excellent.

 

Conclusions

 

We conclude it is feasible to carry out high-quality studies on PA in developing countries. We hope the present manuscript will be useful to other researchers interested in carrying out similar studies.

 

Key-words: accelerometry, adolescent, body composition, measurement, motion sensors, physical activity assessment.

 

2- Physical activity and body composition indices in Brazilian adolescents

 

ABSTRACT

 

Objective: To explore the association between physical activity measured by accelerometers and body composition indices in a sample of adolescents living in a population undergoing rapid nutritional transition.

 

Design: Population-based cross-sectional study nested to the 1993 Pelotas 5 (Brazil) Birth Cohort.

 

Subjects: 457 boys and girls (80.5% of the target sample, 52.1% boys).

 

Measurements: Physical activity was measured by the Actigraph accelerometer. The outcomes investigated were sum of triceps and subscapular skinfolds, waist circumference, 10 waist-to-hip ratio and waist-to-thigh ratio.

 

Results: After adjustment for sex, socioeconomic status, age, Tanner stage of sexual maturation, diet pattern, height, and birth weight, time (min/day) spent at vigorous intensity activity was inversely associated with waist circumference and sum of skinfolds. A one minute increase in vigorous intensity physical activity was associated with a reduction of 15 0.15cm in waist circumference (p=0.007) and 0.20mm in sum of skinfold thicknesses (p=0.02). Associations were stronger in boys than in girls. Total activity and time spent in moderate intensity physical activities were not associated with any of the outcomes in the adjusted analyses.

 

Conclusion: Promotion of improvements in body composition in adolescents should focus on 20 vigorous intensity, instead of moderate intensity physical activities.

 

Keywords: Brazil, accelerometry, adiposity, body fat, motor activity, activity monitors.

 

3- Physical activity as a predictor of adolescent body fatness: a systematic review

 

ABSTRACT

Adolescent obesity has increased dramatically in several countries in recent decades, however the contribution of physical activity level to adolescent adiposity requires clarification. The aim of this review was to investigate the effect of physical activity on subsequent levels of adiposity in adolescence. We also evaluate methodological aspects of the studies included in the review, particularly in terms of measurement accuracy for both exposure (physical activity) and outcome (adiposity) variables. Systematic searches of the literature were undertaken using online databases, including Pubmed/Medline,

examination of citations, and contacting of authors. The online databases were searched from their earliest records until 2007. Only longitudinal studies with 50 or more adolescents were included. Two independent reviewers assessed the quality of the studies using the Downs & Black checklist. Thirteen observational, five experimental and six quasi-experimental studies (without control group) were identified. Almost all studies were carried out in high-income settings and showed protective effects of physical activity for both prevention and treatment of adolescent obesity. However, experimental studies undertaken with obese adolescents at baseline usually combined physical activity with dietary changes, making difficult to assess the effect of physical activity itself on the treatment of obesity. Physical activity estimated from questionnaires and body mass index (BMI) were the most frequently measures. Despite the feasibility of using these approaches in epidemiological studies, significant limitations are evident. Questionnaires are subjective and adolescents may not report physical activity level accurately. Furthermore, BMI is not an accurate measure of fatness for adolescents, as it is also associated with lean mass, hence bias may arise from its longitudinal association with physical activity level. We conclude that despite the majority of studies reviewed showing protective effects of physical activity on adiposity, particularly in individuals obese at baseline, the current literature on this issue is sparse and several methodological drawbacks are evident. The main limitations relate to a lack of validity in the measurements of both physical activity and body composition. Further studies are needed in order to generate evidence-based recommendations for the quantity and quality dose of adolescent physical activity required to prevent or treat adolescent obesity.

 

Keywords: motor activity; adiposity; obesity; youth; exercise; body composition; longitudinal studies