Waist-to-height ratio and body mass index as indicators of cardiovascular risk in youth.

BACKGROUND: The purpose of this investigation was to determine if waist-to-height ratio (WHTR) or body mass index (BMI) is the better indicator of cardiovascular disease risk in children and adolescents of varying ages. METHODS: Data from children and adolescents (N = 2300) who were part of the 2003-2004 National Health and Nutrition Examination Survey (NHANES) were analyzed. Chi-square analyses (2 × 2) were used to compare risk levels of WHTR (>0.50) and BMI (>85th percentile) to systolic blood pressure (SBP) (>90th percentile) as well as total cholesterol (TC) (>200 mg(.) dL(-1) ) for the entire cohort and specified age groups. RESULTS: Significant relationships were detected between SBP and WHTR and BMI, respectively, for the entire cohort as well as the 2 oldest subsamples. A significant association was also noted for both WHTR and BMI to TC for the entire sample and the eldest age group. CONCLUSIONS: A significant association was observed between indicators of cardiovascular health risk and both WHTR and BMI in the entire NHANES cohort of boys and girls as well as in the older age groups. The younger groups of participants did not display a notable link between these cardiovascular indicators and WHTR or BMI.

Electromyographic (EMG) analysis of quadriceps muscle fatigue in children with cerebral palsy during a sustained isometric contraction.

The purpose of this investigation was to determine whether changes in surface electromyography (EMG) data during an isometric muscle protocol, in combination with maximal voluntary isometric force, provide information on fatigue occurrence and exercise limitation in children with cerebral palsy. Twelve children with cerebral palsy and 10 age-matched controls completed an assessment of quadriceps muscle fatigue on an isokinetic device with surface EMG measurements, during a sustained isometric contraction at 50% of the maximal voluntary isometric force. The EMG data collected in participants with cerebral palsy suggest that muscle fatigue occurred sooner in children with cerebral palsy relative to the age-matched controls. However, the results demonstrate that no difference was found in time to exhaustion between the able-bodied and participants with cerebral palsy. These contrasting results may be the result of spasticity and co-contraction during maximal testing, which may play an important role in exercise limitation in children with cerebral palsy.

Within- and between-day stability of treadmill walking VO2 in children with hemiplegic cerebral palsy. Stability of walking VO2 in children with CP.

Within- and between-day stability in locomotor energy use was quantified in 13 children with hemiplegic CP. During testing, subjects were familiarized with the laboratory environment (Session 1), performed three 5-min level treadmill walks (Trials 1, 2, and 3) at 0.67 m x s-1 (Session 2), and completed a single 5-min walk (Trial 4) at 0.67 m x s-1 (Session 3). In Sessions 2 and 3, HR was assessed and expired air was collected and analyzed to determine VO2. Data analyses revealed no significant difference (P > 0.05) in either net VO2 (ml x kg-1 x min-1) or EEIHR (b x m-1) across the three trials performed in Session 2 and between average measures of net VO2 and EEIHR quantified in Session 2 and those obtained in Session 3. Mean within-day coefficient of variation (CV) values for net VO2 and EEIHR were 8.6% +/- 8.5% and 13.9% +/- 7.8%, respectively. Analysis of between-day variability and energy expenditure revealed a between-day CV value of 13.1% for net VO2 and 24.0% for EEIHR. In addition, significant inverse relationships between GMFM scores and within-day (r = -0.61) and between-day (r = -0.58) CV values for net VO2 were detected. Viewed in concert, these data suggest that fairly stable within- and between-day measures of locomotor energy expenditure during level treadmill walking can be achieved in subjects with hemiplegic CP if testing is preceded by a short period of treadmill accommodation. However, children with greater motor dysfunction may require an extended period of treadmill accommodation to reduce trial-to-trial variability in walking energy use.

Within- and between-day stability of treadmill walking VO2 in children with hemiplegic cerebral palsy, stability of walking VO2 in children with CP.

Within- and between-day stability in locomotor energy use was quantified in 13 children with hemiplegic cerebral palsy (CP). During testing, subjects were familiarized with the laboratory environment (Session 1), performed three 5 min level treadmill walks (Trials 1-3) at 0.67 m*s(-1) (Session 2), and completed a single 5 min walk (Trial 4) at 0.67 m*s(-1) (Session 3). In Sessions 2 and 3, heart rate (HR) was assessed and expired air was collected and analyzed to determine VO2. Data analyses revealed no significant difference (P > 0.05) in either net VO2 (ml kg(-1)*min(-1)) or EEI(HR) (b*m(-1)) across the three trials performed in Session 2 and between average measures of net VO2 and EEI(HR) quantified in Session 2 and those obtained in Session 3. Mean within-day coefficient of variation (CV) values for net VO2 and EEI(HR) were 8.6% +/- 8.5% and 13.9% +/- 7.8%, respectively. Analysis of between-day variability and energy expenditure revealed a between-day CV value of 13.1% for net VO2 and 24.0% for EEI(HR). In addition, significant inverse relationships between Gross Motor Function Measure (GMFM) scores and within- (r = -0.61) and between-day (r = -0.58) CV values for net VO2 were detected. Viewed in concert, these data suggest that fairly stable within- and between-day measures of locomotor energy expenditure during level treadmill walking can be achieved in subjects with hemiplegic CP if testing is preceded by a short period of treadmill accommodation. However, children with greater motor dysfunction may require an extended period of treadmill accommodation to reduce trial-to-trial variability in walking energy use.

Comparison of direct and indirect measures of walking energy expenditure in children with hemiplegic cerebral palsy.

The purpose of this study was to investigate the use of the heartrate (HR) version of the energy expenditure index (EEIHR) as a proxy for measurement of walking oxygen consumption (VO2) in children with cerebral palsy (CP). Thirteen children (eight males, five females; mean age 11 years 2 months [SD 3 years], age range 6 to 15 years) with hemiplegic CP, participated in this study. The study was conducted over three sessions. During session 1, participants were familiarized with testing procedures and given 5 minutes of treadmill walking practice. In session 2, participants completed three 5-minute walking bouts on the treadmill at 0.67m x s(-1) to familiarize themselves with treadmill locomotion. During the final session participants walked at 0.67, 0.89, and 1.12m x s(-1) for 5 minutes while gross oxygen consumption (gross VO2; walking VO2/speed), net VO2 ([walking VO2-resting VO2]/speed), and EEIHR ([walking HR-resting HR]/speed) were measured during the last 2 minutes of each bout. Correlational analyses indicated no relationship (p>0.05) between measures of gross VO2 and EEIHR at each speed. Although no association was evident between net VO2 and EEIHR at 0.67 and 0.89m x s(-1), a moderate relationship (r=0.64; p<0.05) was present between these variables at 1.12m x s(-1). Examination of individual data revealed that most participants displayed an unmatched pattern of response between net VO2 and EEIHR. Our results suggest that caution should be applied when using EEIHR to estimate walking energy expenditure in children with CP.

Longitudinal stratification of gait economy in young boys and girls: the locomotion energy and growth study.

The purpose of this study was to determine if the relative ordering of locomotor oxygen consumption ( VO(2)) values remains stable as healthy children age. Beginning at age 6 and ending at age 10, VO(2) during level treadmill walking and running was quantified in 15 boys and 18 girls who were tested on an annual basis. Following 30 min of treadmill accommodation to each exercise mode, subjects walked and ran for 5 min at 1.34 m s(-1) and 2.23 m s(-1), respectively. During the last 2 min of each 5-min stage, expired gas samples were collected and analyzed to quantify VO(2). For both walking (W) and running (R), 27% of subjects showed an average yearly change in VO(2) rank order of

Effects of resistance versus aerobic training on coronary artery disease risk factors.

Individuals exhibiting "the metabolic syndrome" have multiple coronary artery disease risk factors, including insulin resistance, hyperlipidemia, hypertension, and android obesity. We performed a randomized trial to compare the effects of aerobic and resistance training regimens on coronary risk factors. Twenty-six volunteers who exhibited android obesity and at least one other risk factor for coronary artery disease were randomized to aerobic or resistance training groups. Body mass index, waist-to-hip ratio, glucose, insulin, body composition, 24-hr urinary albumin, fibrinogen, blood pressure, and lipid profile were measured at baseline and after 10 weeks of exercise training. Both groups showed a significant reduction in waist-to-hip ratio and the resistance training group also showed a reduction in total body fat. There was no significant change in mean arterial blood pressure in either group. Fasting plasma glucose, insulin, total cholesterol, low-density lipoprotein (LDL) cholesterol, and triglycerides were unchanged in both groups. High-density lipoprotein (HDL) cholesterol increased (13%) with aerobic training only. Plasma fibrinogen was increased (28% and 34%, P < 0.02) in both groups and both groups showed a significant decrease (34% and 28%, P < 0.03) in microalbuminuria after their respective training regimen. In conclusion, resistance training was effective in improving body composition of middle-aged obese sedentary males. Only aerobic training was effective in raising HDL cholesterol. More studies are warranted to assess the effects of exercise on plasma fibrinogen and microalbuminuria.

Prediction of the aerobic demand of walking in children.

PURPOSE: The purpose of this study was to develop a generalized equation to predict VO2 during level treadmill walking in young boys and girls. METHODS: On an annual basis from ages 6 to 10, 23 able-bodied children (14 girls, 9 boys) completed six 5-min walking bouts at speeds ranging from 40.2 to 107.2 m x min(-1). Before testing, each child received 60 min of treadmill walking practice. During the last 2 min of each walking trial, a 2-min sample of expired gas was collected in a meteorological balloon and analyzed to determine VO2. RESULTS: Stepwise regression analyses indicated that the following equation was best suited to predict walking VO2: VO2 = 24.852 + 0.003214 (walking speed in m x min(-1))2 - 0.995 (age in yr) - 0.263 (walking speed); R = 0.95; SEE = 1.74 mL x kg(-1) x min(-1). Bland-Altman analysis revealed that 95% of the differences between actual and predicted VO2 values fell within a range of 3.39 to -3.43 mL x kg(-1) x min(-1). CONCLUSION: We conclude that VO2 during level treadmill walking can be predicted accurately in healthy young children.

Longitudinal profiles of oxygen uptake during treadmill walking in able-bodied children: the locomotion energy and growth study.

The purpose of this study was to document age-related changes in walking V(O(2)) in able-bodied boys and girls. Beginning at age 6 and ending at age 10, 23 children (14 girls, 9 boys) performed six 5-min bouts of level treadmill walking at 0.67, 0.89, 1.12, 1.34, 1.56, and 1.79 m s(-1) on an annual basis. Prior to data collection, subjects received 60 min of treadmill walking practice. During the last 2 min of each walking bout, a 2-min sample of expired air was collected in a meteorological balloon and analyzed to determine V(O(2)). Averaged across age, interindividual variation in V(O(2)) ranged from 32 to 41%. Repeated-measures analysis of variance demonstrated a speed by age interaction for V(O(2)), such that mean V(O(2)) rose (P< or = 0.05) across the five fastest speeds for 6-, 7-, 8-, and 10-year olds and increased over the entire speed range for 9-year olds. For all speeds, V(O(2)) decreased yearly from the ages of 6 to 8. When averaged across speeds, V(O(2)) was 27% higher for 6-year olds compared with 10-year olds. From a clinical perspective, access to longitudinal measurements of walking V(O(2)) in able-bodied children should be helpful in interpreting gait energy use in children with movement disorders and evaluating treatment strategies designed to reduce the aerobic demand of locomotion in youth with impaired mobility.