The health benefits of muscular fitness for children and adolescents: a systematic review and meta-analysis

Assessing the sustained impact of a school-based obesity prevention program for adolescent boys: the ATLAS cluster randomized controlled trial

BACKGROUND

Obesity prevention interventions targeting 'at-risk' adolescents are urgently needed. The aim of this study is to evaluate the sustained impact of the 'Active Teen Leaders Avoiding Screen-time' (ATLAS) obesity prevention program.

METHODS

Cluster RCT in 14 secondary schools in low-income communities of New South Wales, Australia. Participants were 361 adolescent boys (aged 12-14 years) 'at risk' of obesity. The intervention was based on Self-Determination Theory and Social Cognitive Theory and involved: professional development, fitness equipment for schools, teacher-delivered physical activity sessions, lunch-time activity sessions, researcher-led seminars, a smartphone application, and parental strategies. Assessments for the primary (body mass index [BMI], waist circumference) and secondary outcomes were conducted at baseline, 8- (post-intervention) and 18-months (follow-up). Analyses followed the intention-to-treat principle using linear mixed models.

RESULTS

After 18-months, there were no intervention effects for BMI or waist circumference. Sustained effects were found for screen-time, resistance training skill competency, and motivational regulations for school sport.

CONCLUSIONS

There were no clinically meaningful intervention effects for the adiposity outcomes. However, the intervention resulted in sustained effects for secondary outcomes. Interventions that more intensively target the home environment, as well as other socio-ecological determinants of obesity may be needed to prevent unhealthy weight gain in adolescents from low-income communities.

TRIAL REGISTRATION

Australian Clinical Trial Registry ACTRN12612000978864.

A school-based intervention incorporating smartphone technology to improve health-related fitness among adolescents: rationale and study protocol for the NEAT and ATLAS 2.0 cluster randomised controlled trial and dissemination study

INTRODUCTION

Physical inactivity has been described as a global pandemic. Interventions aimed at developing skills in lifelong physical activities may provide the foundation for an active lifestyle into adulthood. In general, school-based physical activity interventions targeting adolescents have produced modest results and few have been designed to be 'scaled-up' and disseminated. This study aims to: (1) assess the effectiveness of two physical activity promotion programmes (ie, NEAT and ATLAS) that have been modified for scalability; and (2) evaluate the dissemination of these programmes throughout government funded secondary schools.

METHODS AND ANALYSIS

The study will be conducted in two phases. In the first phase (cluster randomised controlled trial), 16 schools will be randomly allocated to the intervention or a usual care control condition. In the second phase, the Reach, Effectiveness, Adoption, Implementation and Maintenance (Re-AIM) framework will be used to guide the design and evaluation of programme dissemination throughout New South Wales (NSW), Australia. In both phases, teachers will be trained to deliver the NEAT and ATLAS programmes, which will include: (1) interactive student seminars; (2) structured physical activity programmes; (3) lunch-time fitness sessions; and (4) web-based smartphone apps. In the cluster RCT, study outcomes will be assessed at baseline, 6 months (primary end point) and 12-months. Muscular fitness will be the primary outcome and secondary outcomes will include: objectively measured body composition, cardiorespiratory fitness, flexibility, resistance training skill competency, physical activity, self-reported recreational screen-time, sleep, sugar-sweetened beverage and junk food snack consumption, self-esteem and well-being.

ETHICS AND DISSEMINATION

This study has received approval from the University of Newcastle (H-2014-0312) and the NSW Department of Education (SERAP: 2012121) human research ethics committees. This study is funded by the Australian Research Council (FT140100399) and the NSW Department of Education.

TRIAL REGISTRATION NUMBER

ACTRN12615000360516; Pre-results.

Association between serum adiponectin levels and muscular fitness in Portuguese adolescents: LabMed Physical Activity Study

BACKGROUND AND AIM

Paradoxically, recent investigations have showed that adiponectin levels are inversely associated with muscle strength. However, to date, there is a lack of knowledge on the relationship between muscular fitness (MF) and adiponectin levels in adolescents. We aimed to examine the independent associations between MF and adiponectin levels in adolescents, controlling for several potential confounders.

METHODS AND RESULTS

This is a cross-sectional analysis with 529 Portuguese adolescents aged 12-18 years. A MF score was computed as the mean of the handgrip strength and standing long jump standardized values by age and gender. We measured fasting glucose, insulin, HDL-cholesterol, C-reactive protein and adiponectin. Linear regression analysis showed a significant inverse association between adiponectin (Z-score by age and sex) and MF score, after adjustments for age, sex, pubertal stage, socioeconomic status, adherence to the Mediterranean diet, body mass index, HOMA-IR, HDL-cholesterol, C-reactive protein and cardiorespiratory fitness (unstandardized β = -0.176; p < 0.005). Analysis of covariance showed a significant difference between the Low MF/Non-overweight group and the High MF/Non-overweight Group (p < 0.05) and between the Low MF/Non-overweight and High MF/Overweight Group (p < 0.05) (F (5, 523) = 2.262, p = 0.047).

CONCLUSION

Adiponectin circulating levels are inversely and independently associated with MF. In non-overweight adolescents, those with high levels of MF presented lower levels of adiponectin compared to those with Low MF. Likewise, overweight adolescents with High MF presented lower levels of serum adiponectin than non-overweight adolescents with Low MF.

Effects of Resistance Training in Youth Athletes on Muscular Fitness and Athletic Performance: A Conceptual Model for Long-Term Athlete Development

During the stages of long-term athlete development (LTAD), resistance training (RT) is an important means for (i) stimulating athletic development, (ii) tolerating the demands of long-term training and competition, and (iii) inducing long-term health promoting effects that are robust over time and track into adulthood. However, there is a gap in the literature with regards to optimal RT methods during LTAD and how RT is linked to biological age. Thus, the aims of this scoping review were (i) to describe and discuss the effects of RT on muscular fitness and athletic performance in youth athletes, (ii) to introduce a conceptual model on how to appropriately implement different types of RT within LTAD stages, and (iii) to identify research gaps from the existing literature by deducing implications for future research. In general, RT produced small-to-moderate effects on muscular fitness and athletic performance in youth athletes with muscular strength showing the largest improvement. Free weight, complex, and plyometric training appear to be well-suited to improve muscular fitness and athletic performance. In addition, balance training appears to be an important preparatory (facilitating) training program during all stages of LTAD but particularly during the early stages. As youth athletes become more mature, specificity, and intensity of RT methods increase. This scoping review identified research gaps that are summarized in the following and that should be addressed in future studies: (i) to elucidate the influence of gender and biological age on the adaptive potential following RT in youth athletes (especially in females), (ii) to describe RT protocols in more detail (i.e., always report stress and strain-based parameters), and (iii) to examine neuromuscular and tendomuscular adaptations following RT in youth athletes.

Normative Reference Values for Handgrip Strength in Colombian Schoolchildren: The FUPRECOL Study

Ramírez-Vélez, R, Morales, O, Peña-Ibagon, JC, Palacios-López, A, Prieto-Benavides, DH, Vivas, A, Correa-Bautista, JE, Lobelo, F, Alonso-Martínez, AM, and Izquierdo, M. Normative reference values for handgrip strength in Colombian schoolchildren: the FUPRECOL study. J Strength Cond Res 31(1): 217-226, 2017-The primary aim of this study was to generate normative handgrip (HG) strength data for 10 to 17.9 year olds. The secondary aim was to determine the relative proportion of Colombian children and adolescents that fall into established Health Benefit Zones (HBZ). This cross-sectional study enrolled 7,268 schoolchildren (boys n = 3,129 and girls n = 4,139, age 12.7 [2.4] years). Handgrip was measured using a hand dynamometer with an adjustable grip. Five HBZs (Needs Improvement, Fair, Good, Very Good, and Excellent) have been established that correspond to combined HG. Centile smoothed curves, percentile, and tables for the third, 10th, 25th, 50th, 75th, 90th, and 97th percentile were calculated using Cole's LMS method. Handgrip peaked in the sample at 22.2 (8.9) kg in boys and 18.5 (5.5) kg in girls. The increase in HG was greater for boys than for girls, but the peak HG was lower in girls than in boys. The HBZ data indicated that a higher overall percentage of boys than girls at each age group fell into the "Needs Improvement" zone, with differences particularly pronounced during adolescence. Our results provide, for the first time, sex- and age-specific HG reference standards for Colombian schoolchildren aged 9-17.9 years.

Low Muscle Strength Thresholds for the Detection of Cardiometabolic Risk in Adolescents

INTRODUCTION

There is an association between strength and health among adolescents, yet, what remains to be determined is sex-specific cut points for low strength in the detection of risk in this population. The purpose of this study was to determine thresholds of low grip strength in a large cohort (N=1,326) of adolescents.

METHODS

All data were collected between 2005 and 2008, and analyzed in 2014-2015. A cardiometabolic risk score (MetScore) was computed from the following components: percent body fat, fasting glucose, blood pressure, plasma triglyceride levels, and high-density lipoprotein cholesterol. A high-risk cardiometabolic phenotype was characterized as ≥75th percentile of the MetScore. Conditional inference tree analyses were used to identify sex-specific, low normalized strength (grip strength/body mass) thresholds and risk categories.

RESULTS

Lower strength was independently associated with increased odds of the high-risk cardiometabolic phenotype, such that for every 5% decrement of normalized strength, there were 1.48 and 1.45 increased odds (p<0.001) for boys and girls, even after adjusting for cardiorespiratory fitness and physical activity. Conditional tree analysis revealed a high-risk threshold for boys (≤0.33) and girls (≤0.28), as well as an intermediate threshold (boys, >0.33 and ≤0.45; girls, >0.28 and ≤0.36).

CONCLUSIONS

These sex-specific thresholds of low strength can be incorporated into a clinical setting for identifying adolescents that would benefit from lifestyle interventions to improve muscular fitness and reduce cardiometabolic risk.

Effect of Physically Active Academic Lessons on Body Mass Index and Physical Fitness in Primary School Children

BACKGROUND

Preventing overweight and improving physical fitness in primary school children is a worldwide challenge, and physically active intervention programs usually come with the cost of academic instruction time. This study aimed to investigate effects of physically active academic lessons on body mass index (BMI) and physical fitness in primary school children.

METHODS

Dutch children attending second- or third-grade class from 12 primary schools (N = 376; 8.1 ± 0.7 years) were randomly assigned to a 22-week intervention program or to the control group. In addition to measuring BMI before and after the intervention, physical fitness was measured with 5 items of the Eurofit test battery, measuring cardiovascular and muscular fitness.

RESULTS

Multilevel analysis showed a significant interaction effect between condition (intervention vs control) and grade (B = -0.47; p < .05). For third-grade children, BMI of the intervention group did not change significantly during the intervention period, whereas a significant increase was found in the control group. No significant main or interaction effects were found for cardiovascular or muscular fitness.

CONCLUSIONS

The current physically active academic lessons had positive effects on BMI in third-grade children, but had no effects on cardiovascular and muscular fitness.

Two years of school-based intervention program could improve the physical fitness among Ecuadorian adolescents at health risk: subgroups analysis from a cluster-randomized trial

Background

Adolescents with overweight and poor physical fitness have an increased likelihood of developing cardiovascular diseases during adulthood. In Ecuador, a health promotion program improved the muscular strength and speed-agility, and reduced the decline of the moderate-to-vigorous physical activity of adolescents after 28 months. We performed a sub-group analysis to assess the differential effect of this intervention in overweight and low-fit adolescents.

Methods

We performed a cluster-randomized pair matched trial in schools located in Cuenca–Ecuador. In total 20 schools (clusters) were pair matched, and 1440 adolescents of grade 8 and 9 (mean age of 12.3 and 13.3 years respectively) participated in the trial. For the purposes of the subgroup analysis, the adolescents were classified into groups according to their weight status (body mass index) and aerobic capacity (scores in the 20 m shuttle run and FITNESSGRAM standards) at baseline. Primary outcomes included physical fitness (vertical jump, speed shuttle run) and physical activity (proportion of students achieving over 60 min of moderate–to-vigorous physical activity/day). For these primary outcomes, we stratified analysis by weight (underweight, normal BMI and overweight/obese) and fitness (fit and low fitness) groups. Mixed linear regression models were used to assess the intervention effect.

Results

The prevalence of overweight/obesity, underweight and poor physical fitness was 20.3 %, 5.8 % and 84.8 % respectively. A higher intervention effect was observed for speed shuttle run in overweight (β = −1.85 s, P = 0.04) adolescents compared to underweight (β = −1.66 s, P = 0.5) or normal weight (β = −0.35 s, P = 0.6) peers. The intervention effect on vertical jump was higher in adolescents with poor physical fitness (β = 3.71 cm, P = 0.005) compared to their fit peers (β = 1.28 cm, P = 0.4). The proportion of students achieving over 60 min of moderate-to-vigorous physical activity/day was not significantly different according to weight or fitness status.

Conclusion

Comprehensive school-based interventions that aim to improve diet and physical activity could improve speed and strength aspects of physical fitness in low-fit and overweight/obese adolescents.

Trial registration

Clinicaltrials.gov identifier NCT01004367. Registered October 28, 2009.

Electronic supplementary material

The online version of this article (doi:10.1186/s12887-016-0588-8) contains supplementary material, which is available to authorized users.

Dramatic decrease in muscular fitness in the Czech schoolchildren over the Last 20 years

AIM

Obesity and physical inactivity had already reached epidemic, becoming one of the leading causes of death and disability worldwide. The objective of this study was to investigate the current level and a nearly three decades' trend of muscular fitness (MF) and the nutritional state of Czech children.

METHODS

In 2013, cross-sectional epidemiological survey was conducted in schoolchildren with examination of the anthropometric characteristics and measured MF using a UNIFIT test, which normative for MF categories was given as results of national monitoring data collected in 1987. In total 896 current schoolchildren (472 aged 8-9 years and 424 aged 12-13 years) were examined from selected children through stratified sampling from the Czech Republic.

RESULTS

Against 31% of children from 1986 there were 74% of current children classified as "poor" or "below normal" in the MF category (p<0.001). MF was inversely associated with BMI. Poor posture was diagnosed in 24% of children, more frequently in overweight (OW) and obese (OB) children in comparison to normal body weight children (p<0.001). In comparison to 10% of OW and OB children in 1991, using these cut-off points for body mass index references, the current prevalence of OW and OB doubled (19.8%).

CONCLUSIONS

Current Czech schoolchildren showed a doubled prevalence of OW and OB during the last two decades and simultaneously during nearly three decades there were more than doubled prevalence of "poor" or "under normal" MF of children, with overall dramatic decrease of MF in current schoolchildren.

Long-term effects of physically active academic lessons on physical fitness and executive functions in primary school children

Integrating physical activity into the curriculum has potential health and cognitive benefits in primary school children. The aim of this study was to investigate the effects of physically active academic lessons on cardiovascular fitness, muscular fitness and executive functions. In the current randomized controlled trial, 499 second and third graders within 12 primary schools (mean age = 8.1 ± 0.7) were randomized to the intervention (n = 249) or control condition (n = 250). The physically active academic lessons were given for 2 consecutive school years, 22 weeks per year, three times a week, with a duration of 20-30 min per lesson. Multiple tests were administered before, between and after the intervention period, measuring cardiovascular fitness, muscular fitness and executive functions. Multilevel analysis accounted for the nested structure of the children within classes and schools. Results showed a larger improvement in speed-coordination (B = -0.70,P = 0.002) and a lower improvement in static strength (B = -0.92,P < : 0.001) for the intervention group compared with the control group. The current lessons did not result in a significant change in executive functions.

A methodological approach to short-term tracking of youth physical fitness: the Oporto Growth, Health and Performance Study

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.

Assessing physical fitness in preschool children: Feasibility, reliability and practical recommendations for the PREFIT battery

OBJECTIVES

In childhood (>6 years-old) and adolescence, fitness testing is feasible, reliable and related to later health. The purpose of this study was to examine the feasibility and reliability of a field-based fitness-test battery in preschool children.

DESIGN

Repeated measures.

METHODS

A total of 161 preschoolers aged 3 to 5 years participated in the study. Anthropometry, cardiorespiratory fitness, muscular strength and motor fitness were tested twice (2 weeks apart) using weight, height, waist circumference, PREFIT 20m shuttle run, handgrip strength, standing long jump, 4×10m shuttle run and one-leg stance tests, respectively.

RESULTS

The main results indicated that all tests are feasible and highly reliable (mean differences, weight=0.04kg, height=0.22cm, waist circumference=-0.08cm, PREFIT 20m shuttle run=2.00 laps, handgrip strength=-0.24kg and 4×10m shuttle run=0.12s), in preschool children, except for the standing long jump test and one-leg stance test (mean differences of -7.31cm and 8.01s). After some methodological adaptations, reliability for standing long jump was improved in a replication study (i.e. from -7 to -2cm). We observed evidence of heteroscedasticity in the 4×10m shuttle run and one-leg stance tests.

CONCLUSIONS

The PREFIT battery is a feasible and reliable tool to assess physical fitness in preschool children yet standing long jump has shown mixed findings and requires further studies. The one-leg stance test showed poor reliability in our study and if confirmed by future studies, its use in 3 to 5 years-old would not be recommended. Future studies should consider the mean differences provide in this study to explain the changes in test performance.

Influence of physical fitness on cardio-metabolic risk factors in European children. The IDEFICS study

OBJECTIVE

The aim of the study was to assess the associations of individual and combined physical fitness components with single and clustering of cardio-metabolic risk factors in children.

SUBJECTS/METHODS

This 2-year longitudinal study included a total of 1635 European children aged 6-11 years. The test battery included cardio-respiratory fitness (20-m shuttle run test), upper-limb strength (handgrip test), lower-limb strength (standing long jump test), balance (flamingo test), flexibility (back-saver sit-and-reach) and speed (40-m sprint test). Metabolic risk was assessed through z-score standardization using four components: waist circumference, blood pressure (systolic and diastolic), blood lipids (triglycerides and high-density lipoprotein) and insulin resistance (homeostasis model assessment). Mixed model regression analyses were adjusted for sex, age, parental education, sugar and fat intake, and body mass index.

RESULTS

Physical fitness was inversely associated with clustered metabolic risk (P<0.001). All coefficients showed a higher clustered metabolic risk with lower physical fitness, except for upper-limb strength (β=0.057; P=0.002) where the opposite association was found. Cardio-respiratory fitness (β=-0.124; P<0.001) and lower-limb strength (β=-0.076; P=0.002) were the most important longitudinal determinants. The effects of cardio-respiratory fitness were even independent of the amount of vigorous-to-moderate activity (β=-0.059; P=0.029). Among all the metabolic risk components, blood pressure seemed not well predicted by physical fitness, while waist circumference, blood lipids and insulin resistance all seemed significantly predicted by physical fitness.

CONCLUSION

Poor physical fitness in children is associated with the development of cardio-metabolic risk factors. Based on our results, this risk might be modified by improving mainly cardio-respiratory fitness and lower-limb muscular strength.

Screen-based sedentary behavior and associations with functional strength in 6-15 year-old children in the United States

BACKGROUND

Physical strength is associated with improved health outcomes in children. Heavier children tend to have lower functional strength and mobility. Physical activity can increase children's strength, but it is unknown how different types of electronic media use impact physical strength.

METHODS

Data from the NHANES National Youth Fitness Survey (NNYFS) from children ages 6-15 were analyzed in this study. Regression models were conducted to determine if screen-based sedentary behaviors (television viewing time, computer/video game time) were associated with strength measures (grip, leg extensions, modified pull-ups, plank) while controlling for potential confounders including child age, sex, BMI z-score, and days per week with 60+ minutes of physical activity. Grip strength and leg extensions divided by body weight were analyzed to provide measures of relative strength together with pull-ups and plank, which require lifting the body.

RESULTS

The results from the regression models showed the hypothesized inverse association between TV time and all strength measures. Computer time was only significantly inversely associated with the ability to do one or more pull-ups.

CONCLUSIONS

This study shows that television viewing, but not computer/videogames, is inversely associated with measures of child strength while controlling for child characteristics and physical activity. These findings suggest that "screen time" may not be a unified construct with respect to strength outcomes and that further exploration of the potential benefits of reducing television time on children's strength and related mobility is needed.

Mediators of Psychological Well-being in Adolescent Boys

PURPOSE

The aim of this study was to explore the effect of the Active Teen Leaders Avoiding Screen-time (ATLAS) intervention on psychological well-being in adolescent boys and to examine the potential mediating mechanisms that might explain this effect.

METHODS

ATLAS was evaluated using a cluster randomized controlled trial in 14 secondary schools located in low-income communities (N = 361 adolescent boys, mean age = 12.7 ± .5 years). The 20-week intervention was guided by self-determination theory and involved: professional development for teachers, provision of fitness equipment to schools, enhanced school sport sessions, researcher-led seminars, a smartphone application, and parental strategies for reducing screen time. Assessments were conducted at baseline and immediately post intervention (8 months). Psychological well-being was measured using the Flourishing Scale. Motivational regulations (intrinsic, identified, introjected, controlled, and amotivation) and basic psychological needs (autonomy, competence, and relatedness) in school sport, muscular fitness, resistance training skill competency, and recreational screen time were examined as potential mediating mechanisms of the intervention effect.

RESULTS

The intervention effect on well-being was small but statistically significant. Within a multiple mediator model, changes in autonomy needs satisfaction, recreational screen time, and muscular fitness significantly mediated the effect of the intervention on psychological well-being.

CONCLUSIONS

In addition to the physical health benefits, targeted physical activity programs for adolescent boys may have utility for mental health promotion through the mechanisms of increasing autonomy support and muscular fitness and reducing screen time.

Obesity Prevention and Screening

Obesity is widespread, associated with several physical and psychosocial comorbidities, and is difficult to treat. Prevention of obesity across the lifespan is critical to improving the health of individuals and society. Screening and prevention efforts in primary care are an important step in addressing the obesity epidemic. Each period of human development is associated with unique risks, challenges, and opportunities for prevention and intervention. Screening tools for overweight/obesity, although imperfect, are quick and easy to administer. Screening should be conducted at every primary care visit and tracked longitudinally. Screening tools and cutoffs for overweight and obesity vary by age group.

Adiposity, physical activity and neuromuscular performance in children

We investigated the associations of body fat percentage (BF%), objectively assessed moderate-to-vigorous physical activity (MVPA) and different types of physical activity assessed by a questionnaire with neuromuscular performance. The participants were 404 children aged 6-8 years. BF% was assessed using dual-energy x-ray absorptiometry and physical activity by combined heart rate and movement sensing and a questionnaire. The results of 50-m shuttle run, 15-m sprint run, hand grip strength, standing long jump, sit-up, modified flamingo balance, box-and-block and sit-and-reach tests were used as measures of neuromuscular performance. Children who had a combination of higher BF% and lower levels of physical activity had the poorest performance in 50-m shuttle run, 15-m sprint run and standing long jump tests. Higher BF% was associated with slower 50-m shuttle run and 15-m sprint times, shorter distance jumped in standing long jump test, fewer sit-ups, more errors in balance test and less cubes moved in box-and-block test. Higher levels of physical activity and particularly MVPA assessed objectively by combined accelerometer and heart rate monitor were related to shorter 50-m shuttle run and 15-m sprint times. In conclusion, higher BF% and lower levels of physical activity and particularly the combination of these two factors were associated with worse neuromuscular performance.

Muscle Strength and Fitness in Pediatric Obesity: a Systematic Review from the European Childhood Obesity Group

The increasing prevalence of paediatric obesity and related metabolic complications has been mainly associated with lower aerobic fitness while less is known regarding potential musculoskeletal impairments. The purpose of the present systematic review was to report the evidence regarding muscular fitness in children and adolescents with obesity. A systematic article search was conducted between November 2014 and June 2015 using MEDLINE, EMBASE, CINAHL psycINFO, SPORTDiscus and SocINDEX. Articles published in English and reporting results on muscle strength and muscular fitness in children and adolescents aged 6 to 18 years were eligible. Of 548 identified titles, 36 studies were included for analyses. While laboratory-based studies described higher absolute muscular fitness in youth with obesity compared with their lean peers, these differences are negated when corrected for body weight and lean mass, then supporting field-based investigations. All interventional studies reviewed led to improved muscular fitness in youth with obesity. Children and adolescents with obesity display impaired muscular fitness compared to healthy-weight peers, which seems mainly due to factors such as excessive body weight and increased inertia of the body. Our analysis also points out the lack of information regarding the role of age, maturation or sex in the current literature and reveals that routinely used field tests analysing overall daily muscular fitness in children with obesity provide satisfactory results when compared to laboratory-based data.

Physical Fitness in Young Adults Born Preterm

BACKGROUND

Young adults born preterm have higher levels of cardiometabolic risk factors than their term-born peers. Muscular and cardiorespiratory fitness have important cardiometabolic and other health benefits. We assessed muscular, cardiorespiratory, and self-rated fitness in preterm-born young adults.

METHODS

We studied unimpaired participants of the ESTER (Ennenaikainen syntymä ja aikuisiän terveys [Preterm Birth and Early-Life Programming of Adult Health and Disease]) birth cohort study at age 23.3 (SD: 1.2) years: 139 born early preterm (EPT; <34 weeks), 247 late preterm (LPT; 34-36 weeks), and 352 at term (control group). We measured muscular fitness with the number of modified push-ups performed in 40 seconds and maximal handgrip strength of the dominant hand, cardiovascular fitness with heart rate at the end of a 4-minute step test, and self-rated fitness. Data were analyzed with linear regression.

RESULTS

Young adults born EPT (-0.8; 95% confidence interval: -1.5 to -0.1; adjusted for gender, age, and source cohort) and LPT (-0.8; -1.4 to -0.3) performed fewer modified push-ups than controls. Handgrip strength was 23.8 (0.9-46.8) N lower in EPT participants. Cardiorespiratory fitness, measured by submaximal step test, was similar. On a self-rated fitness scale (1-5), the EPT adults reported 0.2 (0.0-0.4) lower scores than controls. After adjustment for early-life confounders, the results remained. They attenuated after further adjustment for mediating factors.

CONCLUSIONS

Young adults born EPT and LPT had lower muscular fitness than controls, which may predispose them to cardiometabolic and other chronic diseases. Adults born EPT also perceived themselves as less fit than controls.

Longitudinal association between preschool fussy eating and body composition at 6 years of age: The Generation R Study

Background

Children’s fussy eating behavior has been related to both underweight and overweight in cross-sectional studies, but the direction of these associations and the relation with more detailed measures of body composition remains unclear. We aimed to examine whether fussy eating at age 4 years is longitudinally related to body mass index (BMI), fat mass index (FMI) and fat-free mass index (FFMI) at 6 years of age.

Methods

This study was embedded in Generation R, a population-based, prospective cohort. Data were available for 4191 children. The Children’s Eating Behaviour Questionnaire (CEBQ), administered at age 4 years, was used to derive a fussy eating profile. This profile is characterized by high scores on food avoidant scales and low scores on food approach scales. At age 6 years, height and weight were measured at our research center. Body fat and fat-free mass were measured using Dual-energy-X-ray absorptiometry. We used age- and sex-specific standard deviation scores (SDS) for all outcomes.

Results

After adjustment for confounders, the fussy eating profile was related to lower BMI-SDS (B = −0.37, 95 % CI: −0.47;−0.26), lower FMI-SDS (B = −0.22, 95 % CI: −0.33;−0.12) and lower FFMI-SDS (B = −0.41, 95 % CI: −0.54;−0.29). When adjusting for baseline BMI at 4 years, the fussy eating profile predicted a 0.11 lower BMI-SDS at age 6 (95 % CI: −0.19;−0.04). This change in BMI was mainly due to a decrease in FFMI (B = −0.19, 95 % CI: −0.29;−0.09). Fussy eaters also had a higher risk of becoming underweight than non-fussy eaters (OR = 2.28, 95 % CI: 1.34;3.87).

Conclusions

Our findings suggest that young fussy eaters are at risk of having a lower fat free mass and of becoming underweight over a 2-year period. This implies that fussy eaters may benefit from careful monitoring to prevent an adverse growth development.

Electronic supplementary material

The online version of this article (doi:10.1186/s12966-015-0313-2) contains supplementary material, which is available to authorized users.

Growth Charts for Muscular Strength Capacity With Quantile Regression

INTRODUCTION

Muscle strength preservation may play an important role in protecting against cardiometabolic diseases, functional decline, musculoskeletal deterioration, and early all-cause mortality. However, sex-specific strength growth charts and curves using data from a U.S.-representative sample and clinically feasible measurement remain to be established.

METHODS

A sample of 7,119 individuals, aged 6-80 years, was included from the 2011-2012 National Health and Nutrition Examination Survey. Analyses were performed in 2015. Grip strength was assessed using a hydraulic handheld dynamometer; peak force values were normalized per body mass. Parametric quantile regression was used to determine unique normalized and absolute strength percentiles for men and women. Responses were fitted with a parametric model, involving six powers of age.

RESULTS

Growth charts and curves were created using output from the quantile regression from reference values of normalized and absolute grip strength corresponding to the fifth, tenth, 25th, 50th, 75th, 90th, and 95th percentiles across all ages. For men, there was a small drop in normalized strength at age 6 years followed by quick growth until about age 25 years. Among women, normalized strength grew gradually until about age 15 years. For both men and women, normalized strength declined throughout middle age and later adulthood; however, these rates were greater among men. More-pronounced patterns of growth and decline were observed for absolute strength in men and women.

CONCLUSIONS

The established strength quantiles can easily be incorporated into a clinical setting for screening individuals that would benefit from lifestyle interventions to improve muscular fitness and reduce health risks.

Physical Fitness Percentiles of German Children Aged 9-12 Years: Findings from a Longitudinal Study

Background

Generating percentile values is helpful for the identification of children with specific fitness characteristics (i.e., low or high fitness level) to set appropriate fitness goals (i.e., fitness/health promotion and/or long-term youth athlete development). Thus, the aim of this longitudinal study was to assess physical fitness development in healthy children aged 9–12 years and to compute sex- and age-specific percentile values.

Methods

Two-hundred and forty children (88 girls, 152 boys) participated in this study and were tested for their physical fitness. Physical fitness was assessed using the 50-m sprint test (i.e., speed), the 1-kg ball push test, the triple hop test (i.e., upper- and lower- extremity muscular power), the stand-and-reach test (i.e., flexibility), the star run test (i.e., agility), and the 9-min run test (i.e., endurance). Age- and sex-specific percentile values (i.e., P₁₀ to P₉₀) were generated using the Lambda, Mu, and Sigma method. Adjusted (for change in body weight, height, and baseline performance) age- and sex-differences as well as the interactions thereof were expressed by calculating effect sizes (Cohen’s d).

Results

Significant main effects of Age were detected for all physical fitness tests (d = 0.40–1.34), whereas significant main effects of Sex were found for upper-extremity muscular power (d = 0.55), flexibility (d = 0.81), agility (d = 0.44), and endurance (d = 0.32) only. Further, significant Sex by Age interactions were observed for upper-extremity muscular power (d = 0.36), flexibility (d = 0.61), and agility (d = 0.27) in favor of girls. Both, linear and curvilinear shaped curves were found for percentile values across the fitness tests. Accelerated (curvilinear) improvements were observed for upper-extremity muscular power (boys: 10–11 yrs; girls: 9–11 yrs), agility (boys: 9–10 yrs; girls: 9–11 yrs), and endurance (boys: 9–10 yrs; girls: 9–10 yrs). Tabulated percentiles for the 9-min run test indicated that running distances between 1,407–1,507 m, 1,479–1,597 m, 1,423–1,654 m, and 1,433–1,666 m in 9- to 12-year-old boys and 1,262–1,362 m, 1,329–1,434 m, 1,392–1,501 m, and 1,415–1,526 m in 9- to 12-year-old girls correspond to a “medium” fitness level (i.e., P₄₀ to P₆₀) in this population.

Conclusions

The observed differences in physical fitness development between boys and girls illustrate that age- and sex-specific maturational processes might have an impact on the fitness status of healthy children. Our statistical analyses revealed linear (e.g., lower-extremity muscular power) and curvilinear (e.g., agility) models of fitness improvement with age which is indicative of timed and capacity-specific fitness development pattern during childhood. Lastly, the provided age- and sex-specific percentile values can be used by coaches for talent identification and by teachers for rating/grading of children’s motor performance.

Assessment of handgrip strength in preschool children aged 3 to 5 years

We investigated whether there is an optimal grip span for determining the maximum handgrip strength in preschool children and if it is influenced by gender, age, or hand size. A total of 292 preschool children (3-5 years; 59.2% boys) carried out the handgrip strength test with different grip spans (4.0, 4.5, 5.0, 5.5, and 6.0 cm). The hand size was also measured. We also determined the reliability of the optimal grip span in another group of children (n = 56, 57% boys) who did the test twice, with a 3-hour difference between tests. The results showed that 4.0 cm is the optimal grip span to determine the maximum handgrip strength in preschool children. This result applied to both genders, all age groups, and hand sizes. Paired t-tests showed no significant differences between test and retest. These findings may guide clinicians and researchers in selecting the optimal grip span when measuring handgrip strength in preschool children.Level IV.

Physical Activity and Fitness of First Nations Youth in a Remote and Isolated Northern Ontario Community: A Needs Assessment

Among a group of First Nations youth, this research aimed to obtain objective measures of anthropometry, physical activity (PA) and fitness; to identify any group-level differences by sex, body mass index, waist circumference and body fat categories; to assess the barriers and supports to PA. Youth participated in anthropometric measures (BMI, waist circumference, body fat percentage), PA assessment (3 days of accelerometry) and fitness testing (guided by the Canadian Physical Activity, Fitness and Lifestyle Approach). Barriers and supports were assessed via environmental scan and focus groups. Descriptive statistics were compared to reference data. Group differences by sex, BMI status, waist circumference and body fat categories were tested using Mann-Whitney U and Chi square tests (p ≤ 0.05). Qualitative data were assembled into one file and coded manually for categories and themes. Seventy-two youth (12.1 ± 1.1 years, 61.1% male) participated in at least one measure; 36 completed the accelerometry. Sixty-three percent were overweight or obese, 51% were abdominally obese and 21% had excess body fat. Most (86.1%) met Canada's PA guidelines. Boys were more active than girls (p = 0.025) and had greater cardiorespiratory endurance (p = 0.003). Overweight, obese, or abdominally obese youth had lower cardiorespiratory endurance than normal weight youth (p < 0.001). Barriers and supports fell under the main themes: motivation, role models, personnel and facilities, environment and programs. Based on this assessment, youth in this community are active, but not sufficiently physically fit, especially among those affected by obesity and abdominal obesity. The findings, in addition to the numerous barriers to PA, support the community's desire for school-based PA programming.

Citius, Altius, Fortius: beneficial effects of resistance training for young athletes: Narrative review

The motto of the Olympic Games is Citius, Altius, Fortius which is Latin for 'Faster, Higher, Stronger'. It is a clarion call to all competitors, including the youngest, to engage in training strategies that prepare athletes to be the best in the world. Existing research indicates that various forms of resistance training can elicit performance improvements in young athletes. Stronger young athletes will be better prepared to learn complex movements, master sport tactics, and sustain the demands of training and competition. An integrative training programme grounded in resistance training and motor skill development can optimise a young athlete's potential to maximise their athletic and sporting performance, while reducing the risk of a sports-related injury. Resistance training may be especially important for modern-day young athletes who are more likely to specialise in one sport at an early age at the expense of enhancing general physical fitness and learning diversified sport skills. Structured interventions that include qualified instruction; targeted movement practice; and strength and conditioning activities that are developmentally appropriate, progressive and technique driven are needed to attain a level of athleticism that is consistent with the Olympic motto.

Improving health-related fitness in adolescents: the CrossFit Teens™ randomised controlled trial

The aim of this study was to evaluate the preliminary efficacy and feasibility of the CrossFit Teens™ resistance training programme for improving health-related fitness and resistance training skill competency in adolescents. This assessor-blinded randomised controlled trial was conducted in one secondary school in the Hunter Region, Australia, from July to September 2013. Ninety-six (96) students (age = 15.4 (.5) years, 51.5% female) were randomised into intervention (n = 51) or control (n = 45) conditions for 8-weeks (60 min twice per week). Waist circumference, body mass index (BMI), BMI-Z score (primary outcomes), cardiorespiratory fitness (shuttle run test), muscular fitness (standing jump, push-up, handgrip, curl-up test), flexibility (sit and reach) and resistance training skill competency were measured at baseline and immediate post-intervention. Feasibility measures of recruitment, retention, adherence and satisfaction were assessed. Significant group-by-time intervention effects were found for waist circumference [-3.1 cm, P < 0.001], BMI [-1.38 kg · m(‒)(2), P < 0.001], BMI-Z [-0.5 z-scores, P < 0.001], sit and reach [+3.0 cm, P < 0.001], standing jump [+0.1 m, P = 0.021] and shuttle run [+10.3 laps, P = 0.019]. Retention rate was 82.3%. All programme sessions were delivered and participants' mean satisfaction scores ranged from 4.2 to 4.6 out of 5. The findings demonstrate that CrossFit Teens™ is a feasible and efficacious programme for improving health-related fitness in adolescents.

BMI as a mediator of the relationship between muscular fitness and cardiometabolic risk in children: a mediation analysis

Objective

Muscular fitness levels have been associated with cardiometabolic risk in children, although whether body weight acts as a confounder or as an intermediate variable in this relationship remains controversial. The aim of this study was to examine whether the association between muscular fitness and cardiometabolic risk factors is mediated by body mass index (BMI).

Design and Methods

Cross-sectional study using a sample of 1158 schoolchildren aged 8-11 years from the province of Cuenca, Spain. We measured anthropometrics and biochemical variables and we calculated a muscular fitness index as the sum of z-scores of handgrip dynamometry/weight and standing long jump, and we estimated a previously validated cardiometabolic risk index (CMRI). Linear regression models were fitted for mediation analysis to assess whether the association between muscular fitness and cardiometabolic risk was mediated by BMI.

Results

Children with normal weight (NW) had a better cardiometabolic risk profile than their overweight (OW) or obese (OB) peers after controlling for muscular fitness. Marginal estimated mean±SE values for NW, OW and OB categories of CMRI were -0.75±0.06<0.84±0.10<2.18±0.16 in boys and -0.73±0.06<0.96±0.10<2.71±0.17 in girls, both p<0.001. Children with higher levels of muscular fitness had a better cardiometabolic risk profile (CMRI marginal estimated mean±SE 1.04±0.13>0.05±0.09>-1.16±0.13 for lower, middle and upper quartiles of muscular fitness in boys and 1.01±0.16>0.10±0.09>-1.02±0.15 in girls, both p<0.001), but differences disappeared when controlling for BMI. BMI acted as a full mediator between muscular fitness and most cardiometabolic risk factors (Sobel test z=-11.44 for boys; z=-11.83 for girls; p<0.001 in CMRI mediation model) and as a partial mediator in the case of waist circumference (Sobel test z=-14.86 for boys; z=-14.51 for girls; p<0.001).

Conclusions

BMI mediates the association between muscular fitness and cardiometabolic risk in schoolchildren. Overall, good muscular fitness is associated with lower cardiometabolic risk, but particularly when accompanied by normal weight.

Development and implementation of a smartphone application to promote physical activity and reduce screen-time in adolescent boys

PURPOSE

To describe the development and implementation of a smartphone application (app) designed to promote physical activity and reduce screen-time in adolescent boys considered "at-risk" of obesity.

METHODS

An app was developed to support the delivery of a face-to-face school-based obesity prevention program known as the "Active Teen Leaders Avoiding Screen-time" (ATLAS) program. ATLAS was guided by self-determination theory and social cognitive theory and evaluated using a cluster randomized controlled trial with 361 boys (12.7 ± 0.5 years) in 14 secondary schools. Following the completion of the study, participants in the intervention group completed a process evaluation questionnaire and focus groups were conducted with 42 students to explore their general perceptions of the ATLAS program and their experience with the smartphone app. Barriers and challenges encountered in the development, implementation, and evaluation of the app are also described.

RESULTS

Participation in the study was not contingent on ownership of a smartphone, but 70% of participants in the intervention group reported having access to a smartphone or tablet device. Focus group participants reported an enjoyment of the program, and felt that it had provided them with new skills, techniques, and routines for the future. However, their engagement with the smartphone app was limited, due to a variety of reasons. Barriers to the implementation and evaluation of the app included limited access to smartphone devices, technical problems with the push notifications, lack of access to usage data, and the challenges of maintaining participants' interest in using the app.

CONCLUSION

Although participants reported high levels of satisfaction with the ATLAS program in general, the smartphone app was not used extensively. Additional strategies and features may be needed to enhance engagement in adolescent boys.