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BACKGROUND: There has been a decline in children's physical fitness in recent decades. Such concerns are largely based on evidence from North America, Europe, and Asia. The current study describes the secular trend and variation (spread) in the physical fitness scores of young Brazilians from 2005 to 2022. METHODS: This study is a repeated, cross-sectional surveillance study (1999-2022). Children and adolescents (n = 65 139; boys = 36 539) participated between 2005 and 2022. In each cohort six physical fitness tests were conducted: (1) 20-m sprint speed (m s-1 ), (2) cardio-respiratory 6-min run test (m min-1 ), (3) abdominal strength test (sit-ups per min), (4) horizontal jump test (cm), (5) the agility test (m s-1 ), and (6) the medicine ball throw test (cm). Means and distributional characteristics of the population were assessed using ANOVA, ANCOVA adopting BMI as the body-size covariate, Levene's test of equality-of-error variances, and Box and whisker plots. RESULTS: ANOVAs and ANCOVA's identified significant declines in physical fitness over time/year in 5 of the 6 physical fitness variables (e.g., 20-m sprint speed slope B = -0.018 (m s-1 y-1 ); 95% CI -0.019 to -0.017; p < 0.001), the only exception being the medicine ball throw test (cm). The Levene's test of equality-of-error variances also identified a systematic increase in the variances/standard deviations over time/years. CONCLUSIONS: Results provide powerful evidence that children and adolescents' physical fitness is declining, a trend that is also diverging asymmetrically, becoming more extreme in more recent years. The "fit" appear to be getting fitter, but the fitness of the "less-fit" appears to be declining further. These results have important implications for sports medicine and government policy makers.

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ABSTRACT: Guerra, MA Jr, Caldas, LA, Souza, HL, Tallis, J, Duncan, MJ, and Guimarães-Ferreira, L. The effects of physical fitness on postactivation potentiation in professional soccer athletes. J Strength Cond Res 36(6): 1643-1647, 2022-To investigate the relationship of the response to postactivation potentiation (PAP) with scores of physical fitness. Twenty-four professional male soccer players undertook tests of agility, muscular power, aerobic capacity, and body composition. Conditioning activities (CAs) were performed consisting of plyometrics exercises and sprints with sled towing. In the first and second sessions, body composition, agility, power, and aerobic capacity were assessed. At the third session, countermovement jumps (CMJ) were performed with 1, 3, and 5 minutes after the execution of the CA. Significant differences were found for CMJ height 1, 3, and 5 minutes after the CA compared with baseline values (3.58, 5.10, 5.48%, respectively). There was a significant positive correlation between the level of general physical fitness and PAP (CMJ height increase) 5 minutes after (r = 0.73). When the athletes were divided into groups with higher and lower physical fitness, the CA caused a significant increase in CMJ height in both groups, but a significant difference (p < 0.05) was observed at all times after PAP induction, with better performance in higher versus lower fitness level. The results suggest that plyometrics exercises associated with sled towing sprints as a CA result in an increase in CMJ performance in athletes and that physical fitness directly influences the PAP occurrence, with higher fit players demonstrating an enhanced PAP response.

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ABSTRACTThis systematic review and meta-analysis aimed to evaluate the effectiveness of interventions through Physical Education (PE) exercises on bone mineral content (BMC) and density (BMD) of children and adolescents. The research was conducted using the online electronic databases PubMed, Science Direct, Web of Science and Scopus (March 2021). The analysis was restricted to school-based studies that examined the effect of PE interventions on BMC and BMD in schoolchildren (<18 years old). Standardised mean differences (SMD) with 95% confidence interval (CI) and random-effects models were calculated. The heterogeneity and inconsistency of the studies were estimated using Cochran's Q-statistic and I2, respectively. Twenty-two studies with 2,556 participants were selected. PE interventions were associated with a significant increase in BMC (SMD = 1.348; 95% CI, 1.053-1.643) and BMD (SMD = 0.640; 95% CI, 0.417-0.862). Femoral neck subgroup analysis indicate an increase in BMC for boys (SMD = 1.527; 95% CI, 0.990-2.065) and girls (SMD = 1.27; 95% CI, 0.782-1.767), and in BMD for boys (SMD = 0.518; 95% CI, 0.064-0.972) and girls (SMD = 0.817; 95% CI, 0.349-1.284). Finally, increases are reported in the lumbar spine BMC for boys (SMD = 1.860; 95% CI, 1.018-2.700) and girls (SMD = 1.275; 95% CI, 0.782-1.767). This meta-analysis provides insights into the effectiveness of interventions aimed at including physical exercise in PE on bone mass, suggesting that increasing the proportion of curriculum time allocated to PE may improve students' BMD and BMC, especially in the femoral neck and lumbar spine.

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BACKGROUND: Accruing adequate daily amounts of time spent on movement behaviors (physical activity (PA), sedentary behavior (SB), and sleep) in childhood has been associated with positive short and long-term health outcomes. Nonetheless, how waking time is distributed across PA and SB among preschoolers who are short and adequate sleepers at night is unknown. AIM: This study investigated: (1) if there are differences in a movement behaviors composition among adequate and short nocturnal sleepers; and (2) the association between preschoolers' time spent in PA, SB, and sleep among adequate and short nocturnal sleepers. METHODS: A total of 270 preschoolers (132 boys; 3.97 ± 0.81 years old; 15.48 ± 1.62 kg/m2 ) participated in this study. PA and SB were assessed using accelerometry (model wGT3X). Sleep duration was assessed through a parental-proxy interview, and preschoolers were stratified as short and adequate sleepers, according to attendance to international sleep duration guidelines. Compositional data analysis was used to explore the time-use patterns of behaviors among adequate and short sleepers. RESULTS: Short sleepers spent 64 min less time asleep, accumulated 32 min in more sedentary time (p = .005, Cohen's d = 0.36, Bayes Factor: 6.17), and 24 min more in light PA (p = .0005, Cohen's d = 0.44, Bayes Factor: 46.37) compared to adequate sleepers. CONCLUSIONS: Being a short sleeper was associated with greater time spent in SB and light PA during their waking hours. The health implications of movement behaviors composition among short sleep preschoolers should be further investigated.

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This study identifies physical activity (PA) and sedentary behaviour (SB) clusters in preschoolers compliant (C) or non-compliant (NC) with sleep recommendations; and associates these clusters with obesity markers. PA and SB were objectively assessed (Actigraph WGT3-X) in 272 preschoolers (4.4 ± 0.7 years old). Sleep duration was parent-reported, and preschoolers were classified as C (3-4 years old: 600-780 min/day; 5 years old: 540-660 min/day) or NC with sleep recommendations. Body mass index (BMI) and waist circumference (WC) were assessed according to international protocols. Moderate to vigorous physical activity (MVPA) and light physical activity (LPA) were categorized as low/high (<60 min/>60 min/day or <180 min/180 min/day, respectively). SB was defined according to mean values between clusters. Latent profile analysis was performed. Associations between the observed clusters and obesity markers were determined using linear regression (RStudio; 1.3.1073). Four cluster solutions for C and NC preschoolers were identified. A negative association between C/Low MVPA cluster and BMI, and a positive association between NC/Low MVPA and BMI (ß = -0.8, 95%CI = -1.6;-0.1, and ß = 0.9, 95%CI = 0.1;1.7, respectively) were observed. No association was seen for SB clusters. Adequate sleep duration may have a protective role for preschoolers' BMI, even if the children do not comply with MVPA recommendations.

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The purpose of the current article was to use allometric models to identify the best body size descriptors and other anthropometric variables, body composition, and offset maturity that might be associated with the youngsters' 50m personal-best (PB) swim speeds (m·s-1). Eighty-five competitive swimmers (male, n=50; 13.5±1.8 y; female, n=35; 12.6±1.8 y) participated in this study. Height, body mass, sitting height, arm span, skinfolds, arm muscle area (AMA), and maturity offset were assessed. Swimming performance was taken as the PB time recorded in competition, and the propulsive force of their arm (PFA) was assessed by the tied swimming test. The multiplicative allometric model relating 50m PB swim speeds (m·s-1) to all the predictor variables found percentage body fat as a negative [(BF%) ß= -.121±.036; P=0.001], and PFA (PFA ß=.108±.033; P=0.001) and the girl's arm span (ß=.850±.301; P=0.006), all log-transformed, as positive significant predictors of log-transformed swim speed. The adjusted coefficient of determination, Radj2 was 54.8% with the log-transformed error ratio being 0.094 or 9.8%, having taken antilogs. The study revealed, using an allometric approach, that body fatness and PFA were significant contributors to 50m freestyle swim performance in young swimmers.

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BACKGROUND: Although the association between body mass index (BMI), physical activity (PA) and motor competence (MC) has been widely investigated, the influence of different environmental contexts is not well defined. AIM: To analyse the relationship between BMI, PA and MC and the moderating role of the environmental context. SUBJECTS AND METHODS: A cross-sectional study was performed with 668 children (318 boys) aged 5-7 years (north-eastern district - Brazil). MC (Körper koordination test fur Kinder; KTK), BMI and PA (parent reporting) were assessed. To classify three contexts of the environment a variable was created based on the presence of a sports court in school and/or environment for play or sports practice out of school. Multilevel mixed-effects linear regressions, interaction test and estimation of coefficients in moderation analysis were used. RESULTS: BMI (ß = -2.93; p < .01) and age (ß = 19.02; p < .01) were associated, and PA was not associated (ß = 0.07; p = .05) with MC. The strength of the association between BMI and MC changed based on the environmental contexts. The better the environment context the weaker the association between BMI and MC (ß = -2.93, p < .01 to ß = -2.38, p = .33 to ß = 0.26, p = .94). CONCLUSIONS: The association between BMI and MC is moderated by environmental contexts.

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BACKGROUND: In response to the worldwide increasing prevalence of low cardiorespiratory fitness (CRF), several interventions have been developed. The aim of this study was to examine the effect of a school-based intervention on CRF in Brazilian students. METHODS: A nonrandomised controlled design tested 432 students (intervention group: n = 247) from 6th to 9th grade recruited from two public secondary schools in Florianopolis, in 2015. The intervention entitled "MEXA-SE" (move yourself), applied over 13 weeks, included four components: (1) increases in physical activity during Physical Education classes; (2) active recess; (3) educational sessions; and (4) educational materials. CRF (20-m shuttle run test) was the primary outcome. RESULTS: The effect size of the intervention on CRF was 0.15 (CI 95% = -0.04; 0.34). In the within-group comparisons, VO2max decreased significantly from baseline to follow-up in the control group but remained constant in the intervention group. After adjustment variables, differences between intervention and control group were not statistically significant (p > 0.05). CONCLUSION: The "MEXA-SE" intervention did not have an effect on adolescents' CRF. However, maintenance of VO2max in intervention group and a reduction within control group demonstrates that this intervention may be beneficial for long-term CRF and, possibly, the increased intervention time could result in a better effect.

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BACKGROUND: Post-activation potentiation (PAP) is the phenomenon by which muscular performance is enhanced in response to a conditioning stimulus. PAP has typically been evidenced via improved counter movement jump (CMJ) performance. This study examined the effects of PAP, with and without prior caffeine ingestion, on CMJ performance. METHODS: Twelve male professional soccer players (23 ± 5 years) performed two trials of plyometric exercises and sled towing 60 min after placebo or caffeine ingestion (5 mg.kg- 1) in a randomized, counterbalanced and double-blinded design. CMJ performance was assessed at baseline and 1, 3 and 5 min after the conditioning stimulus (T1, T3 and T5, respectively). RESULTS: Two way ANOVA main effects indicated a significant difference in jump height after the PAP protocol (F[3, 11] = 14.99, P < 0.001, partial η2 = 0.577). Analysis also indicated a significant difference in CMJ performance across conditions, with caffeine eliciting a greater response (F[1, 11] = 10.12, P = 0.009, partial η2 = 0.479). CMJ height was increased at T1, T3 and T5 in caffeine condition (5.07%, 5.75% and 5.40%, respectively; P < 0.01) compared to baseline. In the placebo condition, jump performance was increased at T3 (4.94%; P < 0.01) only. Jump height was higher in caffeine condition on T1, T3 and T5 (P < 0.05) but not on baseline (P > 0.05) compared to placebo. CONCLUSIONS: The results of this study suggest that acute plyometric and sled towing stimuli enhances jump performance and that this potentiation is augmented by caffeine ingestion in male soccer players.

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OBJECTIVES: In low- to middle-income countries, children from less-deprived areas (from families of higher socio-economic status [SES]) have superior muscular fitness than those from low-SES groups. They are also taller and heavier, factors associated with muscular fitness. The purpose of this study was to identify any socio-demographic differences in Colombian children's muscular fitness and examine how these conclusions can be modified by scaling for differences in body size. METHODS: A total of 38,098 youths (46% girls), ninth grade students (aged 14-15 years), participated in a study of cross-sectional design. We recorded SES and family incomes, stature, and mass. Standing broad jump and handgrip strength were used to assess muscular fitness. A multiplicative allometric model was adopted to adjust for body-size differences. RESULTS: Children from the mid- to high-SES groups jumped significantly higher than children from the lowest SES group, although no SES group difference in grip strength was observed. After adjusting for body size, children from higher SES and with higher family incomes had significantly lower handgrip strength, and their superior jump height performances remained but were greatly reduced. Only children from the highest SES now jumped significantly higher that the lowest SES group. CONCLUSIONS: The superior jump performance and no difference in handgrip strength of Colombian children from higher SES may simply reflect their superior physiques. When body size is accounted for, these differences are reduced or even reversed, suggesting that children from higher SES groups should not be complacent regarding their apparent superior muscular fitness.

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To compare high active (HA) and low active (LA) adolescent's physical activity (PA) levels in three different domains: commuting to school, physical education (PE) class and recess time at school. Method: This is a cross-sectional study, with a quantitative approach and random sample of 176 (105 girls) adolescents aged 14 - 18 years old from 10 urban public high schools in southern from Brazil. PA levels were measured using a pedometer. The average number of steps was recorded on the way to school, during PE classes and during school recess time. Participants were classified as HA and LA according to Tudor-Locke's cut-off points. Data were analyzed using descriptive statistics and One-Way ANOVA stratified by sex. Results: Data showed differences of mean values between school commuting PA for girls (LA: 1057.60; HA: 1624.54; Δ: 566.94; p<0.001), during PE class (LA: 1401.75, HA: 1701.10; Δ: 308.53; p<0.05) and in recess time (LA: 443.09, HA: 611.98; Δ: 168.89; p=0.001), whereas for boys, differences only found between the mean values of PA during PE class (LA: 1787.91, HA: 2511.20; Δ: 723.29; p<0.01). Conclusion: HA girls are consistently more active in each domain analyzed compared to LA counterparts, while for boys PE class was the domain that differentiated the HA vs. LA adolescents. This study highlights some potential settings to be included in the policies focused in enhance PA levels among adolescents namely in the context of school PE.(AU)

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OBJECTIVES: Both waist circumference (WC) and body size (height) increase with age throughout childhood. Hence, there is a need to scale WC in children to detect differences in adiposity status (eg, between populations and different age groups), independent of body size/height. METHODS: Using two culturally different samples, 1 English (10-15.9 years n = 9471) and 2 Colombian (14-15 years, n = 37,948), for WC to be independent of height (HT), a body shape index was obtained using the allometric power law WC = a.HTb . The model was linearized using log-transformation, and multiple regression/ANCOVA to estimate the height exponents for WC controlling for age, sex, and any other categorical/population differences. RESULTS: In both samples, the power-law height exponent varied systematically with age. In younger children (age 10-11 years), the exponent was approximately unity, suggesting that pre-pubertal children might be geometrically similar. In older children, the height exponent declined monotonically to 0.5 (ie, HT0.5 ) in 15+ year-olds, similar to the exponent observed in adults. UK children's height-adjusted WC revealed a "u" shaped curve with age that appeared to reach a minimum at peak-height velocity, different for boys and girls. Comparing the WC of two populations (UK versus Colombian 14-15-year-old children) identified that the gap in WC between the countries narrowed considerably after scaling for height. CONCLUSIONS: Scaling children's WC for differences in height using allometric modeling reveals new insights into the growth and development of children's WC, findings that might well have been be overlooked if body size/height had been ignored.

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