BackgroundThe relationship between muscle strength and cardiometabolic risk factors in youth, and the potential influence of vitamin D status on this relationship, is not well understood. This study examined associations between muscle strength and dyslipidemia, serum 25-hydroxyvitamin D [25(OH)D], and weight status in diverse schoolchildren.MethodsMeasures of hand-grip strength (standardized for sex and body weight), anthropometrics (height and weight converted to BMI z-score [BMIz]), sociodemographics, and fasting blood concentrations of plasma HDL-C and triglycerides and serum 25(OH)D were collected from 350 4th-8th grade schoolchildren (11.2 ± 1.3 y, 49.4% female, 56.3% non-white/Caucasian). Logistic regression was used to measure associations between standardized tertiles of grip strength and blood lipids, 25(OH)D, and weight status along with associations between 25(OH)D and dyslipidemia and weight status.ResultsChildren with higher grip strength had lower odds of overweight/obesity (OR: 0.03, 95% CI: 0.01-0.06, in the highest tertile of grip strength vs. lowest, p for trend< 0.0001), borderline/low HDL-C (OR: 0.28, 95% CI: 0.16-0.50, p for trend< 0.0001), and borderline/high triglycerides (OR: 0.48, 95% CI: 0.25-0.92, p for trend< 0.05), adjusting for covariates. Associations between blood lipids and grip strength became non-significant after further adjustment for BMIz. No association was observed between grip strength and 25(OH)D, nor between 25(OH)D and borderline/low HDL-C or weight status; however, vitamin D sufficiency was associated with lower odds of borderline/high triglycerides compared with vitamin D deficiency (OR: 0.26, 95% CI: 0.09-0.74, p for trend< 0.05) before BMIz adjustment.ConclusionAmong racially/ethnically diverse children, muscle strength was associated with lower dyslipidemia. Longitudinal studies are needed to explore whether changes in muscle strength impact this relationship in children, independent of weight status.Trial registrationThis study was registered at www.clinicaltrials.gov (No. NCT01537809) on February 17, 2012.

We formulated a "one-size-fits-all" model that predicts the energy requirements of level human walking from height, weight, and walking speed. Our three-component model theorizes that the energy expended per kilogram per stride is independent of stature at mechanically equivalent walking speeds. We measured steady-state rates of oxygen uptake of 78 subjects who spanned a nearly twofold range of statures (1.07-2.11 m) and sevenfold range of body masses (16-112 kg) at treadmill speeds from 0.4 to 1.9 m/s. We tested the size independence of the model by deriving best-fit equations in the form of the model on four stature groups (n ≥ 15): short, moderately short, moderately tall, and tall. The mean walking metabolic rates predicted by these four independently derived equations for the same set of reference subjects (n = 16; stature range: 1.30-1.90 m) agreed with one another to within an average of 5.2 ± 3.7% at the four intermediate speeds in our protocol. We next evaluated the model's gross predictive accuracy by dividing our 78 subjects into 39 stature-matched pairs of experimental and validation group subjects. The model best-fit equation derived on the experimental group subjects predicted the walking metabolic rates of the validation group subjects to within an average of 8.1 ± 6.7% (R(2) = 0.90; standard error of estimate = 1.34 ml O2·kg(-1)·min(-1)). The predictive error of the American College of Sports Medicine equation (18.0 ± 13.1%), which does not include stature as a predictor, was more than twice as large for the same subject group. We conclude that the energy cost of level human walking can be accurately predicted from height, weight, and walking speed.

Highlights School employee health and well-being directly impact student learning and success. Higher physical activity levels were associated with better cardiometabolic health. High stress had a negative impact on the relationship between PA and BMI. Stress may affect heart health, potentially through an impact on health behaviors. Enhancing school employee well-being may improve student academic achievement.

BackgroundThe majority of US children do not meet physical activity recommendations. Schools are an important environment for promoting physical activity in children, yet most school districts do not offer enough physical activity opportunities to meet recommendations. This study aimed to identify school districts across the country that demonstrated exemplary efforts to provide students with many physical activity opportunities and to understand the factors that facilitated their programmatic success.MethodsA total of 59 districts were identified as model districts by members of the Physical Activity and Health Innovation Collaborative, an ad hoc activity associated with the Roundtable on Obesity Solutions at the National Academies of Sciences, Engineering, and Medicine. Semi-structured interviews were conducted with consenting stakeholders from 23 school districts to understand physical education and activity efforts and elucidate factors that led to the success of these districts’ physical activity programming. Districts were geographically and socioeconomically diverse and varied in their administrative and funding structure.ResultsMost districts did not offer the recommended 150 or 225 min of physical activity a week through physical education alone; yet all districts offered a range of programs outside of physical education that provided additional opportunities for students to be physically active. The average number of school-based physical activity programs offered was 5.5, 3.5 and 2.1 for elementary, middle and high schools, respectively. Three overarching and broadly relevant themes were identified that were associated with successfully enhancing physical activity opportunities for students: soliciting and maintaining the support of champions, securing funding and/or tangible support, and fostering bi-directional partnerships between the district and community organizations and programs. Not only were these three themes critical for the development of physical activity opportunities, but they also remained important for the implementation, evaluation and sustainability of programs. These themes also did not differ substantially by the socioeconomic status of districts.ConclusionsThese findings demonstrate the success of school districts across the nation in providing ample opportunities for physical activity despite considerable variability in socioeconomic status and resources. These results can inform future research and provide actionable evidence for school districts to enhance physical activity opportunities to students.Electronic supplementary materialThe online version of this article (10.1186/s12889-018-5889-4) contains supplementary material, which is available to authorized users.