Distinct Amino Acid Profile Characterizes Youth With or at Risk for Type 2 Diabetes.

Branched-chain amino acids (BCAAs) and aromatic AAs (AAAs) are associated with increased risk for type 2 diabetes in adults. Studies in youth show conflicting results. We hypothesized that an AA metabolomic signature can be defined to identify youth at risk for ß-cell failure and the development of type 2 diabetes. We performed targeted AA metabolomics analysis on 127 adolescents (65 girls; 15.5 [SD ±1.9] years old, Tanner stage II-V) with normal weight or obesity across the spectrum of glycemia, with assessment of AA concentrations by mass spectrometry, at fasting, and steady state of a hyperinsulinemic-euglycemic clamp, with determination of insulin sensitivity (IS) per fat-free mass (FFM). We measured insulin secretion during a 2-h hyperglycemic clamp and calculated the disposition index per FFM (DIFFM), a measure of ß-cell function. Our results showed that concentration of glycine (Gly) and the glutamine (Gln)-to-glutamate (Glu) ratio were lower, whereas BCAA, tyrosine, and lysine (Lys) concentrations were higher in the groups with obesity and dysglycemia compared with those with normal weight. Gly and Gln-to-Glu ratio were positively related to IS and DIFFM, with opposite relationships observed for BCAAs, AAAs, and Lys. We conclude that a metabolic signature of low Gly concentration and low Gln-to-Glu ratio, and elevated BCAAs, AAAs, and Lys concentrations may constitute a biomarker to identify youth at risk for ß-cell failure.

Hyperglycemia: A determinant of cardiac autonomic dysfunction in youth with obesity across the spectrum of glycemic regulation.

OBJECTIVES: To characterize the determinants of heart rate variability (HRV) in youth with obesity across the glycemia spectrum. METHODS: A total of 94 adolescents, 15 ± 2.1 years (21 with normal weight, 23 with overweight-normal glucose tolerance, 26 with prediabetes and 24 with type 2 diabetes [T2D]) underwent an assessment of body composition (dual-energy x-ray absorptiometry), 2-h oral glucose tolerance test with the calculation of indices of glycemia and insulin sensitivity (IS), inflammatory markers (high-sensitivity C-reactive protein [hs-CRP] and tumour necrosis factor-α [TNF-α]), and HRV by peripheral arterial tonometry. RESULTS: The HRV frequency-domain index (low-frequency to high-frequency ratio [LF/HF]), an estimate of the ratio between sympathetic and parasympathetic activity, increased across the glycemic spectrum, and was highest in T2D compared with the other three groups (p = 0.004). LF/HF correlated with %body fat (r = 0.22, p = 0.04); fasting (r = 0.39, p < 0.001), 2-h (r = 0.31, p = 0.004), and area under the curve glucose (r = 0.32, p = 0.003); hs-CRP (r = 0.33, p = 0.002) and TNF-α (r = 0.38, p = 0.006). In a linear regression model, fasting glucose (ß = 0.39, p = 0.003) and hs-CRP (ß = 0.21, p = 0.09) contributed to the variance in Ln LF/HF independent of IS, %body fat, age, sex, race-ethnicity and Tanner stage (R2 = 0.23, p = 0.013). CONCLUSIONS: Youth with impaired glucose regulation have evidence of cardiac autonomic dysfunction with decreased HRV, and sympathetic overdrive (increased LF/HF). This dysfunction is mainly related to glycemia and systemic inflammation.

The roles of sleep and eating patterns in adiposity gain among preschool-aged children.

BACKGROUND: Short sleep durations are related to risks for obesity in preschool children. However, the underlying mechanism or mechanisms are not clear. OBJECTIVES: We evaluated the relationships between sleep characteristics and body composition, energetics, and weight-regulating behaviors in preschool-aged children, as well as the longitudinal associations between children's sleep and eating patterns and body composition at a 1-year follow-up. METHODS: Data were drawn from a longitudinal study of 118 children aged 3-5 years. Sleep (duration, midpoint, regularity) and physical activity (PA) were measured by accelerometry over 6 consecutive days; total energy expenditure (TEE) was measured using the doubly labeled water method; body composition (fat mass, fat-free mass, and percent body fat) was measured by DXA; and dietary intake (energy intake, timing) was measured using two 24-hour recalls. Multivariable regression was used to estimate interindividual associations of sleep parameters with body composition, PA, TEE, and dietary outcomes and to examine the relationships between sleep and dietary behaviors and body composition 1 year later. RESULTS: Cross-sectionally, later sleep midpoint is associated with having a greater fat mass (0.33; 95% CI: 0.05, 0.60) and a higher percent body fat (0.92; 95% CI: 0.15, 1.70). Later sleep midpoint was associated with delayed morning mealtimes (0.51; 95% CI: 0.28, 0.74) and evening mealtimes (0.41; 95% CI: 0.29, 0.53), higher nighttime energy intakes (45.6; 95% CI: 19.7, 71.4), and lower morning energy intakes (-44.8; 95% CI: -72.0, -17.6). Longitudinally, shorter sleep duration (-0.02; 95% CI: -0.03, 0.00) and later meal timing (0.83; 95% CI: 0.24, 1.42) were associated with higher percent body fat measurements 1 year later. CONCLUSIONS: Shorter sleep duration and later meal timing are associated with adiposity gains in preschoolers.

Adiposity, Insulin Resistance, Cardiorespiratory Fitness, and Bone Health in Hispanic Children.

CONTEXT: Childhood obesity disproportionately affects Hispanic youth. The skeletal system appears to be a target organ of the adverse effects of obesity. Yet, the relationship between adiposity and bone health in youth and the modulating factors are not well understood. OBJECTIVE: This work aims to examine the relationship between adiposity, insulin resistance (IR), cardiorespiratory fitness (CRF), and bone mass in Hispanic youth. METHODS: A total of 951 Hispanic youth (50% male), aged 4 to 19 years, participated in this cross-sectional design study from the Viva La Familia Study at Children's Nutrition Research Center. Bone mineral content (BMC) and density (BMD), lean mass (LM), total body fat mass (FM), truncal FM were obtained using dual-energy x-ray absorptiometry. Fasting glucose and insulin were obtained and the homeostasis model assessment of insulin resistance (HOMA-IR) was calculated. CRF was measured using a treadmill ramp protocol. We applied linear regression models and mediation analyses. RESULTS: Adiposity measures were negatively related to BMC and BMD after accounting for LM and sex. IR negatively contributed whereas CRF positively contributed to the variance in BMC and BMD, more notably in the pubertal age group. In mediation analysis, HOMA-IR partially mediated the negative relationship of adiposity to BMC (standardized indirect effect [IE] = -0.0382; 95% CI, -0.0515 to -0.0264) whereas the sequential IE of HOMA-IR and CRF partially attenuated (IE = -0.0026; 95% CI, -0.0053 to -0.0005) this relationship. Similar findings were seen with BMD as the primary outcome. CONCLUSION: IR mediates the negative relationship between adiposity and bone mass whereas CRF may partially attenuate it.

Estimating circadian phase in elementary school children: leveraging advances in physiologically informed models of circadian entrainment and wearable devices.

STUDY OBJECTIVES: Examine the ability of a physiologically based mathematical model of human circadian rhythms to predict circadian phase, as measured by salivary dim light melatonin onset (DLMO), in children compared to other proxy measurements of circadian phase (bedtime, sleep midpoint, and wake time). METHODS: As part of an ongoing clinical trial, a sample of 29 elementary school children (mean age: 7.4 ± .97 years) completed 7 days of wrist actigraphy before a lab visit to assess DLMO. Hourly salivary melatonin samples were collected under dim light conditions (<5 lx). Data from actigraphy were used to generate predictions of circadian phase using both a physiologically based circadian limit cycle oscillator mathematical model (Hannay model), and published regression equations that utilize average sleep onset, midpoint, and offset to predict DLMO. Agreement of proxy predictions with measured DLMO were assessed and compared. RESULTS: DLMO predictions using the Hannay model outperformed DLMO predictions based on children's sleep/wake parameters with a Lin's Concordance Correlation Coefficient (LinCCC) of 0.79 compared to 0.41-0.59 for sleep/wake parameters. The mean absolute error was 31 min for the Hannay model compared to 35-38 min for the sleep/wake variables. CONCLUSION: Our findings suggest that sleep/wake behaviors were weak proxies of DLMO phase in children, but mathematical models using data collected from wearable data can be used to improve the accuracy of those predictions. Additional research is needed to better adapt these adult models for use in children. CLINICAL TRIAL: The i Heart Rhythm Project: Healthy Sleep and Behavioral Rhythms for Obesity Prevention https://clinicaltrials.gov/ct2/show/NCT04445740.

Metabolic flexibility across the spectrum of glycemic regulation in youth.

BACKGROUNDMetabolic flexibility (MF) refers to the relative ability to utilize lipid and carbohydrate substrates and to transition between them. It is not clear whether MF is impaired in obese youth and what the determining factors are.METHODSWe investigated the determinants of MF (increased respiratory exchange ratio [ΔRER] under insulin-stimulated conditions) in pubertal youth (n = 104; 15.6 ± 1.8 years) with obesity across the spectrum of glucose tolerance compared with normal weight (NW) controls, including body composition (fat-free mass [FFM], %body fat), visceral adipose fat (VAT) (MRI), glycemia, and insulin sensitivity (IS) [3-hour hyperinsulinemic-euglycemic clamp with measurement of lipolysis ([2H5] glycerol), free fatty acids (FFAs), and RER (indirect calorimetry)].RESULTSYouth with prediabetes and type 2 diabetes had lower ΔRER and oxidative and nonoxidative glucose disposal compared with NW, with no significant difference in ΔRER between NW and obese with normal glucose tolerance. In multiple regression analysis, ISFFM (ß = 0.4, P = 0.004), percentage suppression of FFAs (r = 0.26, P = 0.007), and race/ethnicity (ß = -0.23, P = 0.02) contributed to the variance in ΔRER (R2 = 0.30, P < 0.001) independent of percentage body fat (or VAT), sex, Tanner stage, and hemoglobin A1c.ConclusionMF is defective at the extreme of the metabolic phenotype in obese youth with dysglycemia related to a defect in IS limiting substrate utilization.FUNDINGUSDA/ARS Project Number 3092-51000-057.

The relationship of sleep duration and quality to energy expenditure and physical activity in children.

BACKGROUND: Shorter sleep duration has been linked to the risk for obesity in children. The pathways linking sleep duration and quality to the risk of obesity are unclear, particularly the effect of sleep on energetics. OBJECTIVE: We investigated the relationship between sleep duration, quality and timing in children, to the basal metabolic rate (BMR), total energy expenditure (TEE) and physical activity (PA). METHODS: Fifty nine children in two age-groups (5-11 and 12-18 years) underwent evaluation of body composition (DXA), BMR in a room calorimeter, free-living TEE by doubly labelled water method, sleep and PA (7-day Actiheart monitor) during school break. RESULTS: Sleep duration contributed to the variance in BMR (ß = 0.11, P = .009) after adjusting for age-group, sex, lean and fat mass, but not to the variance in TEE. Late sleep timing was related to lower PA. In the younger age-group, children who met recommended sleep duration on ≥50% of the 7 days had higher light PA (P = .03) and lower sedentary time (P = .009). CONCLUSION: Suboptimal sleep is associated with lower BMR, lower PA, and higher sedentary behaviours in young children. Prospective studies are needed to confirm if insufficient sleep duration or late sleep timing contribute to obesity risk by increasing sedentary behaviours and decreasing BMR.

New generation lipid emulsions increase brain DHA and improve body composition, but not short-term neurodevelopment in parenterally-fed preterm piglets.

New generation, multicomponent parenteral lipid emulsions provide key fatty acids for brain growth and development, such as docosahexaenoic acid (DHA) and arachidonic acid (AA), yet the content may be suboptimal for preterm infants. Our aim was to test whether DHA and AA-enriched lipid emulsions would increase activity, growth, and neurodevelopment in preterm piglets and limit brain inflammation. Cesarean-delivered preterm pigs were given three weeks of either enteral preterm infant formula (ENT) or TPN with one of three parenteral lipid emulsions: Intralipid (IL), SMOFlipid (SMOF) or an experimental emulsion (EXP). Activity was continuously monitored and weekly blood sampling and behavioral field testing performed. At termination of the study, whole body and tissue metrics were collected. Neuronal density was assessed in sections of hippocampus (HC), thalamus, and cortex. Frontal cortex (FC) and HC tissue were assayed for fatty acid profiles and expression of genes of neuronal growth and inflammation. After 3 weeks of treatment, brain DHA content in SMOF, EXP and ENT pigs was higher (P < 0.01) in FC but not HC vs. IL pigs. There were no differences in brain weight or neuron density among treatment groups. Inflammatory cytokine TNFα and IL-1ß expression in brain regions were increased in IL pigs (P < 0.05) compared to other groups. Overall growth velocity was similar among groups, but IL pigs had higher percent body fat and increased insulin resistance compared to other treatments (P < 0.05). ENT pigs spent more time in higher physical activity levels compared to all TPN groups, but there were no differences in exploratory behavior among groups. We conclude that a soybean oil emulsion increased select brain inflammatory cytokines and multicomponent lipid emulsions enriched with DHA and AA in parenteral lipids results in increased cortical DHA and improved body composition without affecting short term neurodevelopmental outcomes.

Impact of changes in maternal body composition on birth weight and neonatal fat mass in dichorionic twin pregnancies.

Background: Although the impact of gestational weight gain (GWG) on birth weight in twin pregnancies has been demonstrated, the specific components of GWG have not been delineated for twin gestations. Fetal body composition has been shown to be modifiable in singleton gestations based on nutritional intervention strategies and may prove to have similar modifications in twin gestations. Objective: We aimed to determine the relation of maternal body composition changes to birth weight, birth length, and neonatal fat mass (FM) in dichorionic-diamniotic twin pregnancies. Design: This is a prospective study of 20 women with twin gestations. Comparisons were made between body composition variables during each trimester and for the entire pregnancy and compared with the outcomes of birth weight, neonatal fat percentage, and birth length. Results: GWG within or above compared with below the IOM recommendations was associated with higher birth weights (P = 0.03, P = 0.04, respectively), but also with higher postpartum weight retention (P = 0.001). Total maternal protein gain over the pregnancy was positively associated with birth weight (P = 0.03). Changes in maternal fat-free mass (FFM), total body water (TBW), and FM from the first to the third trimester were not associated with either birth weight or neonatal FM percentage. However, maternal FM change from the second to the third trimester was significantly correlated to neonatal FM percentage (P = 0.02). Third trimester GWG and total protein gain were positively correlated with neonatal birth length (P = 0.02 and 0.03, respectively). Maternal FFM over all 3 trimesters showed a positive relation with neonatal birth length (P = 0.01). Conclusions: Significant increases in maternal protein are associated with greater birth weight and neonatal birth length. Protein accretion, in contrast to TBW and FM gains, may be the most critical component of maternal GWG in dichorionic twin gestations.

Estimated energy requirements increase across pregnancy in healthy women with dichorionic twins.

Background: Estimated energy requirement (EER) has not been defined for twin pregnancy. This study was designed to determine the EER of healthy women with dichorionic-diamniotic (DCDA) twin pregnancies. Objectives: We aimed to estimate energy deposition from changes in maternal body protein and fat; to measure resting energy expenditure (REE), physical activity level (PAL), and total energy expenditure (TEE) throughout pregnancy and postpartum; and to define the EER based on the sum of TEE and energy deposition for twin gestation. Design: This is a prospective study of 20 women with DCDA twin gestations. Maternal EER, energy deposition, REE, TEE, and PAL were obtained during the first, second, and third trimesters of pregnancy and immediately postpartum. A mixed-effects linear regression model for repeated measures with random intercept was used to test for the effects of BMI groups and time. Results: Gains in total body protein (mean ± SD: 2.1 ± 0.7 kg) and fat mass (5.9 ± 2.8 kg) resulted in total energy deposition of 67,042 ± 25,586 kcal between 0 and 30-32 weeks of gestation. REE increased 26% from 1392 ± 162 to 1752 ± 172 kcal/d across the 3 trimesters, whereas TEE increased 17% from 2141 ± 283 to 2515 ± 337 kcal/d. Physical activity decreased steadily throughout pregnancy. Reductions in physical activity did not compensate for the rise in REE and energy deposition, thus requiring an increase in dietary energy intake as pregnancy progressed. EER increased 29% from 2257 ± 325 kcal/d in the first trimester to 2941 ± 407 kcal/d in the second trimester, and stayed consistent at 2906 ± 350 kcal/d in the third trimester. Conclusion: Increased energy intake, on average ∼700 kcal/d in the second and third trimesters when compared with the first trimester, is required to support gestational weight gain and the rise in energy expenditure of DCDA twin pregnancies.

Efficacy of a Community- Versus Primary Care-Centered Program for Childhood Obesity: TX CORD RCT.

OBJECTIVE: This randomized controlled trial was conducted to determine comparative efficacy of a 12-month community-centered weight management program (MEND2-5 for ages 2-5 or MEND/CATCH6-12 for ages 6-12) against a primary care-centered program (Next Steps) in low-income children. METHODS: Five hundred forty-nine Hispanic and black children (BMI ≥ 85th percentile), stratified by age groups (2-5, 6-8, and 9-12 years), were randomly assigned to MEND2-5 (27 contact hours)/MEND/CATCH6-12 (121.5 contact hours) or Next Steps (8 contact hours). Primary (BMI value at the 95th percentile [%BMIp95 ]) and secondary outcomes were measured at baseline, 3 months (Intensive Phase), and 12 months (Transition Phase). RESULTS: For age group 6-8, MEND/CATCH6-12 resulted in greater improvement in %BMIp95 than Next Steps during the Intensive Phase. Effect size (95% CI) was -1.94 (-3.88, -0.01) percentage points (P = 0.05). For age group 9-12, effect size was -1.38 (-2.87, 0.16) percentage points for %BMIp95 (P = 0.07). MEND2-5 did not differentially affect %BMIp95 . Attendance averaged 52% and 22% during the Intensive and Transition Phases. Intervention compliance was inversely correlated to change in %BMIp95 during the Intensive Phase (P < 0.05). In the Transition Phase, %BMIp95 was maintained or rebounded in both programs (P < 0.05). CONCLUSIONS: MEND/CATCH6-12 was more efficacious for BMI reduction at 3 months but not 12 months compared to Next Steps in underserved children. Intervention compliance influenced outcomes, emphasizing the need for research in sustaining family engagement in low-income populations.

Energy Cost of Activities in Preschool-Aged Children.

BACKGROUND: The absolute energy cost of activities in children increase with age due to greater muscle mass and physical capability associated with growth and developmental maturation; however, there is a paucity of data in preschool-aged children. Study aims were 1) to describe absolute and relative energy cost of common activities of preschool-aged children in terms of VO2, energy expenditure (kilocalories per minute) and child-specific metabolic equivalents (METs) measured by room calorimetry for use in the Youth Compendium of Physical Activity, and 2) to predict METs from age, sex and heart rate (HR). METHODS: Energy expenditure (EE), oxygen consumption (VO2), HR, and child-METs of 13 structured activities were measured by room respiration calorimetry in 119 healthy children, ages 3 to 5 years. RESULTS: EE, VO2, HR, and child-METs are presented for 13 structured activities ranging from sleeping, sedentary, low-, moderate- to high-active. A significant curvilinear relationship was observed between child-METs and HR (r2 = .85; P = .001). CONCLUSION: Age-specific child METs for 13 structured activities in preschool-aged children will be useful to extend the Youth Compendium of Physical Activity for research purposes and practical applications. HR may serve as an objective measure of MET intensity in preschool-aged children.

Role of physical activity and sleep duration in growth and body composition of preschool-aged children.

OBJECTIVE: The impact of physical activity patterns and sleep duration on growth and body composition of preschool-aged children remains unresolved. Aims were (1) to delineate cross-sectional associations among physical activity components, sleep, total energy expenditure (TEE), and body size and composition; and (2) to determine whether physical activity components, sleep, and TEE predict 1-year changes in body size and composition in healthy preschool-aged children. METHODS: Anthropometry, body composition, accelerometry, and TEE by doubly labeled water were measured at baseline; anthropometry and body composition were repeated 1 year later (n = 111). RESULTS: Cross-sectionally, positive associations between sedentary activity and weight and fat-free mass (FFM) (P = 0.009-0.047), and a negative association between moderate-vigorous physical activity (MVPA) and percent fat mass (FM) (P = 0.015) were observed. TEE and activity energy expenditure (AEE) were positively associated with weight, body mass index (BMI), FFM, and FM (P = 0.0001-0.046). Prospectively, TEE, AEE, physical activity level, and MVPA, but not sedentary activity, were positively associated with changes in BMI (P = 0.0001-0.051) and FFM (P = 0.0001-0.037), but not percent FM. Sleep duration inversely predicted changes in FM (P = 0.005) and percent FM (P = 0.006). CONCLUSIONS: Prospectively, MVPA, TEE, AEE, and physical activity level promote normal growth and accretion of FFM, whereas sleep duration inversely predicts changes in adiposity in preschool-aged children.

Exploring Metrics to Express Energy Expenditure of Physical Activity in Youth.

BACKGROUND: Several approaches have been used to express energy expenditure in youth, but no consensus exists as to which best normalizes data for the wide range of ages and body sizes across a range of physical activities. This study examined several common metrics for expressing energy expenditure to determine whether one metric can be used for all healthy children. Such a metric could improve our ability to further advance the Compendium of Physical Activities for Youth. METHODS: A secondary analysis of oxygen uptake (VO2) data obtained from five sites was completed, that included 947 children ages 5 to 18 years, who engaged in 14 different activities. Resting metabolic rate (RMR) was computed based on Schofield Equations [Hum Nutr Clin Nut. 39(Suppl 1), 1985]. Absolute oxygen uptake (ml.min-1), oxygen uptake per kilogram body mass (VO2 in ml.kg-1.min-1), net oxygen uptake (VO2 - resting metabolic rate), allometric scaled oxygen uptake (VO2 in ml.kg-0.75.min-1) and YOUTH-MET (VO2.[resting VO2] -1) were calculated. These metrics were regressed with age, sex, height, and body mass. RESULTS: Net and allometric-scaled VO2, and YOUTH-MET were least associated with age, sex and physical characteristics. For moderate-to-vigorous intensity activities, allometric scaling was least related to age and sex. For sedentary and low-intensity activities, YOUTH-MET was least related to age and sex. CONCLUSIONS: No energy expenditure metric completely eliminated the influence of age, physical characteristics, and sex. The Adult MET consistently overestimated EE. YOUTH-MET was better for expressing energy expenditure for sedentary and light activities, whereas allometric scaling was better for moderate and vigorous intensity activities. From a practical perspective, The YOUTH-MET may be the more feasible metric for improving of the Compendium of Physical Activities for Youth.

Energetic adaptations persist after bariatric surgery in severely obese adolescents.

OBJECTIVE: Energetic adaptations induced by bariatric surgery have not been studied in adolescents or for extended periods postsurgery. Energetic, metabolic, and neuroendocrine responses to Roux-en-Y gastric bypass (RYGB) surgery were investigated in extremely obese adolescents. METHODS: At baseline and at 1.5, 6, and 12 months post-baseline, 24-h room calorimetry, body composition, and fasting blood biochemistries were measured in 11 obese adolescents relative to five matched controls. RESULTS: In the RYGB group, mean weight loss was 44 ± 19 kg at 12 months. Total energy expenditure (TEE), activity EE, basal metabolic rate (BMR), sleep EE, and walking EE significantly declined by 1.5 months (P = 0.001) and remained suppressed at 6 and 12 months. Adjusted for age, sex, fat-free mass, and fat mass, EE was still lower than baseline (P = 0.001). Decreases in serum insulin, leptin, and triiodothyronine (T3), gut hormones, and urinary norepinephrine (NE) paralleled the decline in EE. Adjusted changes in TEE, BMR, and/or sleep EE were associated with decreases in insulin, homeostatic model assessment, leptin, thyroid stimulating hormone, total T3, peptide YY3-36, glucagon-like peptide-2, and urinary NE and epinephrine (P = 0.001-0.05). CONCLUSIONS: Energetic adaptations in response to RYGB-induced weight loss are associated with changes in insulin, adipokines, thyroid hormones, gut hormones, and sympathetic nervous system activity and persists 12 months postsurgery.

Effectiveness of the modified progressive aerobic capacity endurance run test for assessing aerobic fitness in Hispanic children who are obese.

The purpose of this study was to evaluate the effectiveness of the progressive aerobic capacity endurance run (PACER) and a newly designed modified PACER (MPACER) for assessing aerobic fitness in Hispanic children who are obese. Thirty-nine (aged 7-12 years) children who were considered obese (≥ 95 th body mass index [BMI] percentile) and 16 children who were considered normal weight (<85th BMI percentile) participated in this study. Performance outcomes included test duration (in minutes) and exercise heart rate (HR) (first-stage and peak HR) for each test. Ninety-five percent confidence intervals and independent t-tests were used to assess differences in primary outcomes. Mean PACER test duration was 1.6 ± 0.6 and 3.1 ± 1.3 minutes for children who were obese and normal weight, respectively. Modified PACER duration was higher than 3 minutes for the obese (3.6 ± 0.6 minutes) and normal weight (5.3 ± 1.2 minutes) groups. Children first-stage HR, expressed as a percent of peak HR, was above the predicted anaerobic threshold during the PACER, but below the anaerobic threshold during the MPACER. Relative first-stage HR was not significantly different between groups for the PACER, but they were significantly different between groups for the MPACER. In conclusion, the MPACER was a better alternative than the PACER for assessing aerobic fitness in Hispanic children who were normal weight and obese. When validated, this modified field test could be used to assess aerobic fitness in Hispanic children, particularly those who are overweight or obese. Additionally, the study provides evidence in which physical educators, personal trainers, and others most apt to assess aerobic fitness in children who are obese, should modify tests originally designed for the population who are normal weight.

Revision of Dietary Reference Intakes for energy in preschool-age children.

BACKGROUND: Dietary Reference Intakes (DRI) for energy aim to balance energy expenditure at a level of physical activity consistent with health and support adequate growth in children. DRIs were derived from total energy expenditure (TEE) measured by using the doubly labeled water (DLW) method; however, the database was limited in the 3-5-y-old range. OBJECTIVE: We reexamined the DRI for energy for preschool-age children. DESIGN: Ninety-seven healthy, normal-weight, preschool-age children (mean ± SD age: 4.5 ± 0.9 y) completed a 7-d DLW protocol while wearing accelerometer and heart rate-monitoring devices. RESULTS: Mean TEE and physical activity level (PAL) averaged 1159 ± 171 kcal/d and 1.34 ± 0.14, respectively. TEE predicted by DRI equations agreed with observed TEE (+34 kcal/d or 3%) if the sedentary PAL category was assumed but was overestimated by using the low active (+219 kcal/d or 19%), active (398 kcal/d or 34%), and very active (593 kcal/d or 51%) PAL categories. PAL categories were redefined on the basis of the narrower PAL range observed in preschoolers (range: 1.05-1.70) compared with older children and adults (range: 1.0-2.5). Sex-specific nonlinear regression models were newly developed to predict TEE from age, weight, height, and new PAL categories. The mean absolute error of TEE prediction equations was 0.00 ± 35 kcal/d or 0.1 ± 3%. Ancillary measures, such as total accelerometer counts and total daily steps, that were significantly correlated (P = 0.01-0.05) with TEE (r = 0.26-0.38), TEE per kilogram (r = 0.31-0.41), and PAL (r = 0.36-0.48) may assist in the classification of preschoolers into PAL categories. CONCLUSIONS: Current DRIs for energy overestimate energy requirements of preschool-age children because of the erroneous classification of children into PAL categories. New TEE prediction equations that are based on DLW and appropriate PAL categories are recommended for preschool-age children. This trial was registered at clinicaltrials.gov as H12067.

Prediction of energy expenditure and physical activity in preschoolers.

PURPOSE: Accurate, nonintrusive, and feasible methods are needed to predict energy expenditure (EE) and physical activity (PA) levels in preschoolers. Herein, we validated cross-sectional time series (CSTS) and multivariate adaptive regression splines (MARS) models based on accelerometry and heart rate (HR) for the prediction of EE using room calorimetry and doubly labeled water (DLW) and established accelerometry cut points for PA levels. METHODS: Fifty preschoolers, mean ± SD age of 4.5 ± 0.8 yr, participated in room calorimetry for minute-by-minute measurements of EE, accelerometer counts (AC) (Actiheart and ActiGraph GT3X+), and HR (Actiheart). Free-living 105 children, ages 4.6 ± 0.9 yr, completed the 7-d DLW procedure while wearing the devices. AC cut points for PA levels were established using smoothing splines and receiver operating characteristic curves. RESULTS: On the basis of calorimetry, mean percent errors for EE were -2.9% ± 10.8% and -1.1% ± 7.4% for CSTS models and -1.9% ± 9.6% and 1.3% ± 8.1% for MARS models using the Actiheart and ActiGraph+HR devices, respectively. On the basis of DLW, mean percent errors were -0.5% ± 9.7% and 4.1% ± 8.5% for CSTS models and 3.2% ± 10.1% and 7.5% ± 10.0% for MARS models using the Actiheart and ActiGraph+HR devices, respectively. Applying activity EE thresholds, final accelerometer cut points were determined: 41, 449, and 1297 cpm for Actiheart x-axis; 820, 3908, and 6112 cpm for ActiGraph vector magnitude; and 240, 2120, and 4450 cpm for ActiGraph x-axis for sedentary/light, light/moderate, and moderate/vigorous PA (MVPA), respectively. On the basis of confusion matrices, correctly classified rates were 81%-83% for sedentary PA, 58%-64% for light PA, and 62%-73% for MVPA. CONCLUSIONS: The lack of bias and acceptable limits of agreement affirms the validity of the CSTS and MARS models for the prediction of EE in preschool-aged children. Accelerometer cut points are satisfactory for the classification of sedentary, light, and moderate/vigorous levels of PA in preschoolers.

Support vector machines classifiers of physical activities in preschoolers.

The goal of this study is to develop, test, and compare multinomial logistic regression (MLR) and support vector machines (SVM) in classifying preschool-aged children physical activity data acquired from an accelerometer. In this study, 69 children aged 3-5 years old were asked to participate in a supervised protocol of physical activities while wearing a triaxial accelerometer. Accelerometer counts, steps, and position were obtained from the device. We applied K-means clustering to determine the number of natural groupings presented by the data. We used MLR and SVM to classify the six activity types. Using direct observation as the criterion method, the 10-fold cross-validation (CV) error rate was used to compare MLR and SVM classifiers, with and without sleep. Altogether, 58 classification models based on combinations of the accelerometer output variables were developed. In general, the SVM classifiers have a smaller 10-fold CV error rate than their MLR counterparts. Including sleep, a SVM classifier provided the best performance with a 10-fold CV error rate of 24.70%. Without sleep, a SVM classifier-based triaxial accelerometer counts, vector magnitude, steps, position, and 1- and 2-min lag and lead values achieved a 10-fold CV error rate of 20.16% and an overall classification error rate of 15.56%. SVM supersedes the classical classifier MLR in categorizing physical activities in preschool-aged children. Using accelerometer data, SVM can be used to correctly classify physical activities typical of preschool-aged children with an acceptable classification error rate.

Predicting metabolic rate across walking speed: one fit for all body sizes?

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.