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BACKGROUND: Studies concerning child and adolescent growth, development, performance and health aimed at the multiple interactions amongst this complex set of variables are not common in the Portuguese speaking countries. AIM: The aim of this paper is to address the key ideas, methodology and design of the Oporto Growth, Health and Performance Study (OGHPS). SUBJECTS AND METHODS: The OGHPS is a multidisciplinary mixed-longitudinal study whose main purpose is to examine the multiple interactions among biological, environmental and lifestyle indicators that affect growth, development, health and performance of Portuguese adolescents aged 10-18 years old. RESULTS: This study briefly presents baseline results for growth, physical fitness and lifestyle behaviours for those participating in the cross-sectional sample (n ≈ 8000). Approximately 30% were over-fat or obese. On average, boys were more physically fit and active than girls. Few adolescents meet the guidelines for sleep duration (≈10%) and eating habits (16.2-24.8%), while 76-85% meet the recommended levels of moderate-to-vigorous physical activity. CONCLUSIONS: The OGHPS has an innovative approach due to its mixed-longitudinal design and the broad array of variables. Furthermore, subsequent analyses of the longitudinal data will enable a detailed exploration of important factors affecting the growth trajectories of health and performance variables and will also help to identify some of the most opportune times for interventions in terms of health behaviours.

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In this paper, three different statistical approaches were used to investigate short-term tracking of cardiorespiratory and performance-related physical fitness among adolescents. Data were obtained from the Oporto Growth, Health and Performance Study and comprised 1203 adolescents (549 girls) divided into two age cohorts (10-12 and 12-14 years) followed for three consecutive years, with annual assessment. Cardiorespiratory fitness was assessed with 1-mile run/walk test; 50-yard dash, standing long jump, handgrip, and shuttle run test were used to rate performance-related physical fitness. Tracking was expressed in three different ways: auto-correlations, multilevel modelling with crude and adjusted model (for biological maturation, body mass index, and physical activity), and Cohen's Kappa (κ) computed in IBM SPSS 20.0, HLM 7.01 and Longitudinal Data Analysis software, respectively. Tracking of physical fitness components was (1) moderate-to-high when described by auto-correlations; (2) low-to-moderate when crude and adjusted models were used; and (3) low according to Cohen's Kappa (κ). These results demonstrate that when describing tracking, different methods should be considered since they provide distinct and more comprehensive views about physical fitness stability patterns.

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Abstract Tracking refers to the idea of maintaining a relative position within a given group of individuals as they change in time. This paper presents several approaches to study and analyze tracking (i.e., stability and predictability) and its application in physical education and sport. We will use data from a mixed-longitudinal study conducted in the city of Porto, Portugal, comprising 486 girls that were divided into two age cohorts: 12-14 years and 14-16 years. Body mass index (BMI) was the chosen variable in all statistical analyses of tracking. Statistical techniques to describe tracking included: autocorrelations, Foulkes & Davis gamma and Goldstein constancy index. Regardless of statistical procedure used, tracking BMI was moderate to high in each cohort, which could be due to the short follow-up period. However, each tracking statistics showed different aspects of inter-individual differences in intra-individual changes of girls' BMI. The use of any of the suggested procedures to study aspects of stability and predictability (i.e., tracking) in longitudinal studies requires a careful scrutiny of main goals and hypotheses to be tested.

Resumo O termo Tracking refere-se à noção de manutenção de posição relativa de valores de um dado grupo de sujeitos em função do tempo. O presente artigo apresenta diversas técnicas de estudo e análise do tracking (i.e., estabilidade e previsibilidade). Os dados utilizados provêm de um estudo longitudinal-misto da Região do Grande Porto, Portugal, compreendendo 486 meninas, divididas em duas coortes que abrangem as faixas etárias dos 12 aos 14 e dos 14 aos 16 anos. A variável eleita para as análises foi o índice de massa corporal (IMC). Os procedimentos estatísticos utilizados para descrever o tracking foram: autocorrelações, gama de Foulkes & Davis e índice de constância de Goldstein. Independentemente da estatística utilizada e face à curta duração do estudo, o tracking do IMC foi moderado a elevado em cada coorte. Contudo, cada procedimento de análise mostrou aspetos distintos das diferenças interindividuais nas mudanças intraindividuais do IMC das meninas. O uso parcimonioso de qualquer um dos procedimentos sugeridos para estudar aspetos da estabilidade e previsibilidade (i.e., do tracking) em estudos longitudinais exige o estabelecimento muito criterioso dos objetivos e hipóteses a serem testados.

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O propósito deste estudo é apresentar o uso da modelação multinível (MMN) com informação oriunda de um estudo longitudinal-misto sobre o crescimento, desenvolvimento e saúde de adolescentes portugueses. A amostra foi composta por 5155 indivíduos divididos em quatro coortes que abrangem as faixas etárias dos 10 aos 12, 12 aos 14, 14 aos 16 e 16 aos 18 anos. As variáveis de estudo foram a força de preensão manual e o percentual de gordura total (%GTotal). A análise mostrou trajetórias curvilíneas do desempenho de força de preensão, com maiores incrementos anuais nos meninos. O %GTtotal apresentou associação positiva com o desempenho da força estática; constatou-se uma forte variabilidade interindividual. O recurso ao delineamento longitudinal-misto permitiu a recolha mais célere da informação; e a metodologia MMN mostrou-se suficientemente flexível e robusta para acomodar, num modelo único, aspectos da mudança individual e das diferenças interindividuais do desempenho da força estática condicionados à ação do tempo.

The main aim of this study was to introduce the use of multilevel modeling in the data from a mixed longitudinal study concerning growth, development and health of Portuguese adolescents. The sample comprises 5155 subjects from 4 age cohorts: 10 to 12, 12 to 14, 14 to 16 and 16 to 18 years. Variables chosen for analysis were handgrip strength and percentage of total body fat. Multilevel modeling analysis showed a quadratic trajectory of adolescents' handgrip strength performance, with higher annual increasing in boys. The percentage of total body fat was positively associated with the static strength and there were marked interindividual differences. The use of a mixed longitudinal design allowed a faster data collection process; in addition, multilevel modeling analysis was sufficiently flexible and robust to accommodate, in a single model, aspects of individual and interindividual changes in static strength development over the time.

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OBJECTIVE: To examine the associations of objectively measured sedentary time and television (TV) viewing time with emerging inflammatory and endothelial function markers in adolescents. STUDY DESIGN: This study comprised 183 adolescents (88 girls), aged 13 to 17 years. Sedentary time and moderate-to-vigorous physical activity was objectively measured with accelerometry, whereas TV viewing time was self-reported. White blood cell counts and levels of C-reactive protein, complement factors C3 and C4, interleukin-6, adiponectin, leptin, intercellular adhesion molecule 1, vascular cell adhesion molecule 1, E-selectin, L-selectin, and plasminogen activator inhibitor-1 were measured in fasted blood samples. RESULTS: Sedentary time was not significantly associated with any of the examined cardiometabolic markers after controlling for potential confounders. However, TV viewing time was positively associated with soluble endothelial adhesion molecules intercellular adhesion molecule 1 (standardized ß = 0.19, P = .008), vascular cell adhesion molecule 1 (ß = 0.17, P = .020), L-selectin (ß = 0.18, P = .013), and E-selectin (ß = 0.16, P = .023) concentrations, after controlling for sex, age, pubertal status, moderate-to-vigorous physical activity, body mass index, and total sedentary time. CONCLUSIONS: High TV viewing time may play a key role in cardiovascular and metabolic diseases through the cell adhesion molecules in adolescence.

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OBJECTIVES: To examine the combined influence of physical activity and screen time (television and video games) on the odds of being overweight and to evaluate the utility of current public policy recommendations. STUDY DESIGN: Physical activity was assessed by a pedometer and screen time was assessed by survey in a sample of 709 children age 7 to 12 years. The percentage of subjects meeting current physical activity and screen time recommendations was calculated. Cross-tabulated physical activity-screen time groups were formed depending on whether or not the children were meeting current recommendations. Logistic regression was used to examine the influence of physical activity and screen time on the odds of being overweight. RESULTS: Children meeting physical activity and screen time recommendations were the least likely to be overweight. Approximately 10% of the boys and 20% of the girls meeting both recommendations were overweight, compared with 35% to 40% of those who did not meet either recommendation. Screen time and physical activity appeared to be equivalent risk factors for boys, even though physical activity in girls was more strongly associated with body mass index. CONCLUSIONS: Children not meeting the physical activity or screen time recommendations were 3 to 4 times more likely to be overweight than those complying with both recommendations.

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