COVID-19 public health crisis has exerted immediate negative impacts on children’s physical fitness, but the longer-term effects are not clear, and the impact on children with excess weight is yet unknown. We examined changes in multiple components of physical fitness in response to COVID-19 imposed restrictions, but also a year after the restrictions were terminated, and compared these trends in groups of boys and girls with normal weight, overweight, or obesity before the pandemic. Information was gathered through Slovenia's national fitness surveillance system, and included 41,330 children (19,890 girls), aged 5–17, who had their fitness levels measured yearly from 2019 to 2022. Multilevel linear mixed models, fitted separately for boys and girls, were used to model the individual-level trends over time in centile score for each fitness test across 3 weight groups. Overall fitness levels decreased markedly across all weight categories between 2019 and 2020, with the largest decreases in Total Fitness Index observed in children with normal weight and overweight (−8.4 and −7.7 centiles for boys and −8.3 and −8.8 for girls, respectively, p < 0.001). While there was some recovery in the overall fitness level between 2020 and 2022, it remained much lower in 2022 compared to 2019 across most groups, apart from boys with obesity. Fitness components that had the largest impact on general fitness trends were cardiorespiratory fitness, lower body power, body core, and upper body strength. A severe decline in fitness that has not come close to returning to pre-pandemic levels in most population groups of youth begs for urgent population-wide initiatives that will provide additional opportunities for physical activity to youth. Among vulnerable groups, girls with overweight and obesity deserve a special focus of these policies. 10.13039/501100007601 Horizon 2020 (Grant no. 774548), Slovenian National Research Agency (Grant no. P5-0142), 10.13039/501100004488 Croatian Science Foundation (Grant no. DOK-2020-01-3728).

Background: A large number of wearable activity monitor models are released and used each year by consumers and researchers. As more studies are being carried out on children and adolescents in terms of sedentary behavior (SB) assessment, knowledge about accurate and precise monitoring devices becomes increasingly important. Objective: The main aim of this systematic review was to investigate and communicate findings on the accuracy and precision of consumer-grade physical activity monitors in assessing the time spent in SB in children and adolescents. Methods: Searches of PubMed (MEDLINE), Scopus, SPORTDiscus (full text), ProQuest, Open Access Theses and Dissertations, DART Europe E-theses Portal, and Networked Digital Library of Theses and Dissertations electronic databases were performed. All relevant studies that compared different types of consumer-grade monitors using a comparison method in the assessment of SB, published in European languages from 2015 onward were considered for inclusion. The risk of bias was estimated using Consensus-Based Standards for the Selection of Health Status Measurement Instruments. For enabling comparisons of accuracy measures within the studied outcome domain, measurement accuracy interpretation was based on group mean or percentage error values and 90% CI. Acceptable limits were predefined as –10% to +10% error in controlled and free-living settings. For determining the number of studies with group error percentages that fall within or outside one of the sides from previously defined acceptable limits, two 1-sided tests of equivalence were carried out, and the direction of measurement error was examined. Results: A total of 8 studies complied with the predefined inclusion criteria, and 3 studies provided acceptable data for quantitative analyses. In terms of the presented accuracy comparisons, 14 were subsequently identified, with 6 of these comparisons being acceptable in terms of quantitative analysis. The results of the Cochran Q test indicated that the included studies did not share a common effect size (Q5=82.86; P<.001). I2, which represents the percentage of total variation across studies due to heterogeneity, amounted to 94%. The summary effect size based on the random effects model was not statistically significant (effect size=14.36, SE 12.04, 90% CI −5.45 to 34.17; P=.23). According to the equivalence test results, consumer-grade physical activity monitors did not generate equivalent estimates of SB in relation to the comparison methods. Majority of the studies (3/7, 43%) that reported the mean absolute percentage errors have reported values of <30%. Conclusions: This is the first study that has attempted to synthesize available evidence on the accuracy and precision of consumer-grade physical activity monitors in measuring SB in children and adolescents. We found very few studies on the accuracy and almost no evidence on the precision of wearable activity monitors. The presented results highlight the large heterogeneity in this area of research. Trial Registration: PROSPERO CRD42021251922; https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=251922

Obesity in childhood has deleterious consequences for health while improving physical fitness can significantly reduce health risks related to high body mass index. We aimed to examine the evolution of disparities in physical fitness based on weight status among 7–15-year-olds in Slovenia between 1989 and 2019 and compare these trends across sex, age and socioeconomic status. We used annual data collected within the SLOfit monitoring system in the period between 1989 and 2019, totalling 4,256,930 participants (about 137 000 per year). We examined cardiorespiratory fitness (600-m run test), muscular fitness (60-s sit-ups, bent arm hang, and standing broad jump test) and skill-related fitness (backwards obstacle course, 60-m dash, arm plate tapping). We grouped children according to the IOTF cut-offs for BMI to those living with normal weight or excess weight and estimated changes in physical fitness over time by fitting quantile regression models separately by sex and age group, and then using segmented regression to identify the patterns of trends over time. Weight-based disparities in physical fitness were large in 1989 and have further increased by 2019. The increase in disparities was generally around 5 percentiles larger in boys, and 10–15-year-olds compared to younger children. It was particularly pronounced for body core strength and speed in boys (up to 15 and 19 percentiles, respectively) and upper body strength and speed among girls (up to 13 percentiles). Most of the increase in disparities in health-related fitness accumulated during the 2010s, when the fitness of children generally improved, but much less so in children living with excess weight. Despite recent improvements in population fitness levels, children with excess weight seem to be left behind, which adds to existing health inequalities. Our results should encourage policymakers to redesign policies aimed at promoting physical activity and enhancing physical fitness to make them more equitable and ultimately lead to reducing inequalities in fitness.

Background Obesity in childhood has deleterious consequences for health while improving physical fitness can significantly reduce health risks related to high body mass index. This study leverages near-census data collected by the national fitness surveillance system in Slovenia to investigate the evolution of weight-based disparities in the physical fitness of 7–15-year-olds between 1989 and 2019. Methods We used annual data collected within the SLOfit monitoring system in the period between 1989–2019, totalling 4,256,930 participants (about 137 000 per year). We examined cardiorespiratory fitness (600-m run test), muscular fitness (60-s sit-ups, bent arm hang, and standing broad jump test) and skill-related fitness (backwards obstacle course, 60-m dash, arm plate tapping). We grouped children according to the IOTF cut-offs for BMI to those living with normal weight or excess weight and estimated changes in physical fitness over time by fitting quantile regression models separately by sex and age group, and then using segmented regression to identify the structure of trends over time. Results Weight-based disparities in physical fitness were large in 1989 and have further increased from 1989 to 2019 for all fitness components and across all age and sex groups. The increase in disparities was generally larger in boys than in girls, and 10–15-year-olds compared to younger children. Most of the increase in disparities in health-related fitness accumulated during the 2010s, when the fitness of children generally improved, but much less so in children living with excess weight. Conclusions Despite recent improvements in population fitness levels, children with excess weight seem to be left behind, which adds to existing health inequalities. Our results should encourage policymakers to redesign policies aimed at promoting physical activity and enhancing physical fitness to make them more equitable and ultimately lead to reducing inequalities in fitness.

Partial sleep deprivation is common in sports, particularly before competitions. This study examined whether two nights of severe sleep restriction (<4 h/night), compared with mild sleep restriction (control), are associated with changes in SJ and CMJ in physically active female students. Twenty-three female students (n = 12 experimental; n = 11 control) were randomly assigned to their respective groups. The experimental group underwent two nights of severe sleep restriction (<4 h/night), while the control group experienced mild sleep restriction. Differences between groups were analyzed using Quade’s nonparametric ANCOVA (sleep duration as covariate), and within-group pre–post changes were evaluated using paired-samples t-tests. No significant differences were found between groups after two nights in CMJ (p = 0.92) or SJ (p = 0.73) performance. Within the experimental group, SJ performance significantly decreased from the initial to the final assessment (p = 0.02), with a large effect size (d = −0.81). CMJ performance in the experimental group showed a non-significant decrease with a moderate effect size (d = −0.45). No significant differences or notable effect sizes were found in the control group (d = 0.01 to 0.23). Within-group results suggest that SJ decreased after severe sleep restriction, while CMJ changes were smaller and not statistically significant; between-group comparisons were not significant, and results appear sensitive to the analytical approach. These exploratory findings suggest that monitoring sleep before power-related tasks may be warranted. Coaches may consider monitoring sleep duration before high-intensity power training, as two nights of severe sleep restriction may be associated with reduced SJ performance.