The purpose of this study was to analyse secular trend in handgrip strength (HGS) in adolescents using an allometric approach and identify the factors associated. The sample comprised 657 and 1004 adolescents (14 to 19 years) in 2007 and 2017/2018, respectively, of public schools in Florianópolis, Brazil. The dependent variable was HGS normalised to body mass and height. Covariance analysis was used to examine secular trends in HGS, and multiple linear regression was used to identify associated factors. The independent variables were sociodemographic, biological, and behavioural factors. Comparison of HGS between surveys indicated a negative secular trend in both sexes (p < 0.001). In boys, there was a positive association of HGS with age and FFM in both surveys. In 2017/18, there was a positive association with sexual maturation and a negative association with sitting time and fat percentage. In girls, FFM was positively associated with HGS in both surveys. In 2007, there were positive associations of HGS with age and vigorous physical activity, whereas, in 2017/18, negative associations were observed with economic level and sitting time. The findings of the present study show a decline in adolescent HGS. And behavioural changes appear to be contributing to declines in HGS.

Objective: To investigate the association of phase angle (PhA) with body fat percentage, lean soft tissue, and bone mineral density (BMD) in adolescent athletes overall and stratified by sex and sexual maturity stage. Approach: A cross-sectional study was conducted with 112 adolescent athletes (67 boys, 14.25 ± 2.08 years) who practiced indoor volleyball, beach volleyball, swimming, Track and Field, or basketball. BMD, lean soft tissue, and body fat percentage were estimated using dual-energy X-ray absorptiometry. PhA was determined using bioelectrical impedance analysis (50 kHz). Associations between PhA and body composition were tested using multiple linear regression in three models: (1) total sample, (2) stratified by sex, and (3) stratified by maturation. Covariates generally included skin color/race, sport modality, time in the sport, and weekly training volume. Main results: In the overall sample, PhA showed a negative association with body fat percentage and a positive association with lean soft tissue and BMD. When the results were stratified by sex, there was a negative association with fat percentage in girls and positive associations with lean soft tissue and BMD in boys. Analysis by sexual maturity stage revealed that PhA was negatively associated with body fat percentage in pubertal athletes and positively associated with lean soft tissue and BMD in both pubertal and post-pubertal athletes. Significance: PhA was positively associated with lean soft tissue and BMD and negatively associated with fat percentage. However, associations varied by sex and sexual maturity, underscoring the importance of accounting for these biological variables when assessing relationships between body composition and PhA in athletes.

Objetivo: Identificar as associações entre aptidão física, atividade física extracurricular e adiposidade corporal em uma amostra representativa de adolescentes de Florianópolis, Brasil. Método: estudo transversal, de base escolar, que incluiu 981 adolescentes de 14 a 18 anos, matriculados em escolas públicas do município de Florianópolis-SC. A variável dependente foi a adiposidade corporal, obtida pela soma de duas dobras cutâneas (tríceps + subescapular). A participação em atividades físicas extracurriculares e os componentes relacionados à saúde da aptidão física (flexibilidade, força e resistência muscular, aptidão cardiorrespiratória) foram considerados variáveis ​​independentes. Resultados: A prevalência de alta adiposidade corporal foi de 27,1%, sem diferença entre os sexos (meninos=25%, meninas=29,4%). Houve associação negativa entre adiposidade corporal, aptidão cardiorrespiratória e resistência abdominal em ambos os sexos. O modelo final explicou 58,2% da variação nos altos escores de adiposidade corporal em meninas e 47,9% em meninos. Em ambos os sexos, foram encontradas associações negativas entre aptidão cardiorrespiratória (meninas: β = -0,752, p= <0,001; meninos: β = -0,655, p< 0,001) e resistência abdominal (meninas: β = -0,070, p = 0,021; crianças: β = -0,077, p= 0,021) com adiposidade corporal. Além disso, nas meninas, foram observadas associações negativas entre atividade física extracurricular (β = -0,078, p= 0,010) e nos meninos força de preensão (β = -0,121, p< 0,001) e flexibilidade (β = -0,082, p = 0,015) com adiposidade corporal. Conclusão: Em ambos os sexos, maiores níveis de aptidão cardiorrespiratória e resistência abdominal estiveram associados a menor adiposidade corporal. Nas meninas, a atividade extracurricular e nos meninos, a força muscular e a flexibilidade associaram-se negativamente com a adiposidade corporal. Palavras-chave: Adolescente. Composição do corpo. Atividade física extracurricular. Cinantropometria.

To examine the link between adherence to 24-h movement guidelines (isolated and combined) and muscular strength, cardiorespiratory fitness, and obesity indicators in Brazilian adolescents. Data from 980 adolescents (14–19 years) in Florianópolis, Brazil, were analyzed. The dependent variables were body mass index (BMI), body fat, handgrip strength (HGS), maximal oxygen consumption ($\dot{\mathrm{V}}$O_2max). The independent variables were physical activity (PA, IPAQ), screen time (ST), sleep (bedtime, wake-up time). Compliance was calculated for each behavior and combinations. Multiple linear regression models were employed. Overall compliance: 4.1% (boys), 4.9% (girls). Positive associations were found between PA adherence and HGS/ $\dot{\mathrm{V}}$O_2max in both sexes, ST adherence and $\dot{\mathrm{V}}$O_2max, and adherence to all three guidelines and $\dot{\mathrm{V}}$O_2max. Girls showed positive associations between combined PA ​+ ​sleep adherence and HGS, ST ​+ ​sleep and $\dot{\mathrm{V}}$O_2max, and negative associations between adherence to two guidelines and BMI. Boys exhibited a negative association between PA and body fat, positive between ST and HGS, and positive/negative between combined PA ​+ ​ST adherence and HGS/body fat. Moreover, adherence to all three guidelines associated positively with HGS. Adhering to 24-h movement guidelines, alone or in combination, benefits muscular strength and cardiorespiratory fitness in Brazilian adolescents. However, simultaneous adherence did not correlate with obesity indicators.

Objective: The aim of this study was to analyze isolated and combined associations of physical inactivity excessive screen time with negative self-rated health, according to sex, among school adolescents. Methods: In this cross-sectional study conducted with 2,517 adolescents in Amazonas State, participants were asked about their self-rated health with the following question: How do you rate your health? Responses were dichotomized into positive (excellent and good) and negative (regular, bad, and terrible). Information on sex, age group, family income, physical activity, and screen time (watching TV, using a computer, or playing video games) was collected through a self-administered questionnaire. Adolescents simultaneously classified as physically inactive (2 h/day) were considered to have two risk factors. Data was analyzed using binary logistic regression. Results: Out of every 10 adolescents, 2 had a negative self-rated health. After adjusting for age and family income, there were no isolated or combined associations between physical inactivity or excessive screen time and negative self-rated health in girls. In boys, negative self-rated health was associated with insufficient levels of physical activity (odds ratio [OR]: 2.39; 95% confidence interval [CI]: 1.03–5.59) and with the accumulation of two risk factors (OR: 1.61; 95%CI 1.10–2.34). Conclusions: Being insufficiently active and the combination of physical inactivity and excessive screen time become exposure factors to the negative self-rated health of adolescent boys.

Objective: Identify possible associations of muscular endurance with body adiposity, physical activity, and sedentary behavior in adolescents. Methods: A cross-sectional study was conducted on a sample of 1773 adolescents (795 boys and 978 girls) aged 14 to 19 years from Florianopolis, Brazil. Abdominal endurance by the sit-up test proposed by the Canadian Physical Activity, Fitness and Lifestyle Assessment Approach. Body adiposity was estimated by the sum of triceps and subscapular skinfold thicknesses. Daily physical activity was estimated by the International Physical Activity Questionnaire - Short Form. Sedentary behavior was investigated using a self-report questionnaire, taking into account the time spent sitting on a weekday and a weekend day. Stepwise linear regression analysis was performed to identify the predictors of abdominal endurance. Results: Boys (16,43 years) were more active (94.85 min/day vs 84.30 min/day, p < 0.001) and had higher abdominal endurance (23.67 repetitions vs 21.31 repetitions, p < 0.001) than girls. Girls (16,27 years) had a longer sitting time (414.89 min/day vs 376.12 min/day, p < 0.001) and higher body adiposity (31.69 mm vs 21.44 mm, p < 0.001) than boys. As for predictors, body adiposity (β = −0.207) was the only variable associated with abdominal endurance in boys, whereas body adiposity (β = −0.127) and physical activity (β = 0.099) were associated with abdominal endurance in girls. Conclusion: In both sexes, high levels of body adiposity negatively affect abdominal endurance. On the other hand, in girls, high levels of physical activity have a positive influence on abdominal endurance.