Cheryl A. Howe

Ten months of exercise improves general and visceral adiposity, bone, and fitness in black girls.

Objective: The goal of this study was to evaluate the impact of a 10‐month after‐school physical activity (PA) program on body composition and cardiovascular (CV) fitness in young black girls.

Accelerometer Output and MET Values of Common Physical Activities

PURPOSE This article 1) provides the calibration procedures and methods for metabolic and activity monitor data collection, 2) compares measured MET values to the MET values from the compendium of physical activities, and 3) examines the relationship between accelerometer output and METs for a range of physical activities. METHODS Participants (N = 277) completed 11 activities for 7 min each from a menu of 23 physical activities. Oxygen consumption (V O2) was measured using a portable metabolic system, and an accelerometer was worn. MET values were defined as measured METs (V O2/measured resting metabolic rate) and standard METs (V O2/3.5 mL.kg.min). For the total sample and by subgroup (age [young < 40 yr], sex, and body mass index [normal weight < 25 kg.m]), measured METs and standard METs were compared with the compendium, using 95% confidence intervals to determine statistical significance (alpha = 0.05). Average counts per minute for each activity and the linear association between counts per minute and METs are presented. RESULTS Compendium METs were different than measured METs for 17/21 activities (81%). The number of activities different than the compendium was similar between subgroups or when standard METs were used. The average counts for the activities ranged from 11 counts per minute (dishes) to 7490 counts per minute (treadmill: 2.23 m.s, 3%). The r between counts and METs was 0.65. CONCLUSIONS This study provides valuable information about data collection, metabolic responses, and accelerometer output for common physical activities in a diverse participant sample. The compendium should be updated with additional empirical data, and linear regression models are inappropriate for accurately predicting METs from accelerometer output.

Blood lactate and perceived exertion relative to ventilatory threshold: boys versus men.

The purpose of this study was to examine blood lactate (BLa) levels and ratings of perceived exertion (RPE) in nine boys (10.5 +/- 0.7 yr) and nine men (25.3 +/- 2.0 yr) during exercise relative to ventilatory threshold (VT). VT and VO2max were determined during a graded exercise test on a cycle ergometer. On three additional days each subject exercised for 10 min at either 80, 100, or 120% of the VO2 at VT. Capillary BLa levels and RPE were assessed at minutes 5 and 10 of each trial. VO2max averaged 47.7 +/- 5.4 and 50.2 +/- 6.2 mL x g(-1) x min(-1) in the boys and men, respectively (P > 0.05). VT expressed as %VO2max was 67.2 +/- 3.5% in the boys and 67.3 +/- 4.9% in the men (P > 0.05). BLa levels ranged from 2.0 +/- 0.7 to 4.7 +/- 0.9 mmol x L(-1) in the boys and from 2.6 +/- 0.5 to 8.2 +/- 2.1 mmol x L(-1) in the men across the three intensities. Corresponding RPE values ranged from 11.2 +/- 1.8 to 16.2 +/- 2.2 in the boys and from 10.2 +/- 1.2 to 15.8 +/- 1.7 in the men. A group x time x intensity interaction (P < 0.05) indicated that BLa in the men increased more so across time and intensity. There were no significant group difference or interactions involving RPE during exercise. Setting exercise intensity relative to VT did not abolish child-adult differences with respect to submaximal BLa levels. Despite maintaining lower BLa levels, RPE values were similar between boys and men.

Accuracy of four resting metabolic rate prediction equations: Effects of sex, body mass index, age, and race/ethnicity

OBJECTIVE This study compared the accuracy of four commonly used RMR prediction equations to measured RMR obtained from the MedGem(®) metabolic analyzer. DESIGN AND METHODS Height, weight and RMR were measured in 362 healthy individuals [51% female; body mass index (BMI): 17.6-50.6 kg m(-2); ages: 18-60 years; 17.4% non-white]. Following a 4h fast, participants rested in the supine position after which RMR was measured. RMR was estimated using four commonly used prediction equations: Harris-Benedict, Mifflin-St. Jeor, Owen, and WHO/FAO/UNU. Accuracy was determined by calculating the percentage of predicted RMR values that were within ± 10% of measured RMR values. Main effects of sex, BMI, age, and race/ethnicity were assessed using repeated measures ANCOVAs. RESULTS For all participants combined, the Harris-Benedict, Mifflin, and WHO/FAU/UNU equations similarly predicted RMR values within ± 10% of measured RMR values (57.5, 56.4, and 55.2% of the sample, respectively). When participant data were stratified by sex, BMI, age, and race/ethnicity, the accuracy of each regression equation varied dramatically. The Harris-Benedict equation over-predicted RMR in 18-29 year olds. The Owen equation under-predicted RMR in both sexes, all three BMI categories, 18-49 year olds and White participants. The Mifflin under-predicted RMR in both sexes, normal weight individuals, 40-60 year olds, and non-Hispanic White participants. The WHO/FAO/UNU over-predicted RMR in males, overweight participants, and 50-60 year olds. CONCLUSIONS When examining the entire sample, the Harris-Benedict, Mifflin, and WHO/FAU/UNU equations yielded similar levels of agreement with the MedGem(®) measured RMR. However, clinical judgment and caution should be used when applying these prediction equations to special populations or small groups.

Accelerometer Prediction of Energy Expenditure: Vector Magnitude Versus Vertical Axis

UNLABELLED It is suggested that triaxial accelerometers (RT3) are superior to single-plane accelerometers for predicting energy expenditure (EE). PURPOSE To compare the RT3 uniaxial and triaxial prediction of activity EE (AEE) during treadmill activities (TM) and activities of daily living (ADL). METHODS Two hundred and twelve subjects (aged 20-60 yr) completed TM speeds of 1.34, 1.56, and 2.23 m x s(-1) at 0% and 3% grades, stair ascent/descent, moving a box, and two randomly assigned ADL. Subjects wore a portable indirect calorimeter to measure EE to calculate AEE by subtracting resting metabolic rate. Acceleration counts in the vertical (V), medial-lateral, and anterior-posterior planes were collected in a single RT3 secured to the hip. Predicted AEE (RT3AEE) was estimated from vector magnitude (VM) counts using a proprietary algorithm. A paired t-test compared RT3AEE versus AEE. The relationship among V and VM counts and AEE was examined using linear regression analyses. RESULTS RT3 overestimated AEE for all activities combined, overestimated for TM (9.0%), and underestimated for ADL (34.3%; P < 0.001). The R2 values between RT3AEE and AEE for TM and ADL were R2 = 0.78 and R2 = 0.15, respectively. The RT3 underestimated activity with greater upper body movements by 24.4%-64.5% (P < 0.001). V and VM counts were similarly related to AEE (R2 = 0.35) and RT3AEE (R2 = 0.83-0.89). CONCLUSIONS Although the RT3 did not accurately predict AEE from accelerometer counts, stronger relationships existed between predicted and measured AEE for TM compared with ADL. Compared with V counts, using VM counts to predict AEE did not significantly improve the relationship between counts and AEE. Analytic techniques beyond linear regression with VM as a covariate or with counts from each axis entering the model separately may improve estimates of AEE from triaxial accelerometers.

Mets and Accelerometry of Walking in Older Adults: Standard versus Measured Energy Cost

PURPOSE This study aimed to measure the metabolic cost (METs) of walking activities in older adults, to examine the relationship between accelerometer output and METs across walking activities, and to compare measured MET values in older adults with the MET values in the compendium. METHODS Twenty older adults (mean age = 75, range = 60-90 yr) completed eight walking activities (five treadmill based, three free living) for 6 min each. Oxygen consumption (V˙O2) and resting metabolic rate (RMR) were measured using a portable metabolic system, and motion was recorded using a waist-mounted ActiGraph accelerometer (GT3X; ActiGraph, Pensicola, FL). Energy expenditure across activities was defined as kilocalories per minute and measured as METs (V˙O2 / RMR) and standard METs (V˙O2 / 3.5 mL·kg-1·min-1). Mixed modeling was used to assess differences in counts per minute and kilocalories per minute by weight status, sex, comorbidity status, and functional status. Linear regression analysis was applied to develop a prediction equation for kilocalories per minute. Energy costs of walking were subsequently compared with METs in the compendium of physical activities. RESULTS Average measured RMR was 2.6 mL·kg-1·min-1, 31.6% less than the standard RMR of 3.5 mL·kg-1·min-1. On average, standard METs were 71% lower than the measured METs across all walking activities. Measured MET levels differed from previously reported values in the literature and values listed in the compendium, resulting in misclassification of activity intensities for 60% of the walking conditions. Average counts for the walking activities ranged from 809 (treadmill = 1.5 mph) to 4593 counts per minute (treadmill = 3.5 mph). Previous regression equations consistently overestimate all activities compared with the measured energy cost in this sample of older adults. CONCLUSION This study identifies the need for equations and cut points specific to older adults.

A recess intervention to promote moderate-to-vigorous physical activity

Schools provide a prime environment for interventions that attempt to increase physical activity and prevent obesity.

Classification Accuracy of the Wrist-Worn Gravity Estimator of Normal Everyday Activity Accelerometer

PURPOSE The purpose of this study was to determine whether the published left-wrist cut points for the triaxial Gravity Estimator of Normal Everyday Activity (GENEA) accelerometer are accurate for predicting intensity categories during structured activity bouts. METHODS A convenience sample of 130 adults wore a GENEA accelerometer on their left wrist while performing 14 different lifestyle activities. During each activity, oxygen consumption was continuously measured using the Oxycon mobile. Statistical analysis used Spearmans rank correlations to determine the relationship between measured and estimated intensity classifications. Cross tabulations were constructed to show the under- or overestimation of misclassified intensities. One-way χ2 tests were used to determine whether the intensity classification accuracy for each activity differed from 80%. RESULTS For all activities, the GENEA accelerometer-based physical activity monitor explained 41.1% of the variance in energy expenditure. The intensity classification accuracy was 69.8% for sedentary activities, 44.9% for light activities, 46.2% for moderate activities, and 77.7% for vigorous activities. The GENEA correctly classified intensity for 52.9% of observations when all activities were examined; this increased to 61.5% with stationary cycling removed. CONCLUSIONS A wrist-worn triaxial accelerometer has modest-intensity classification accuracy across a broad range of activities when using the cut points of Esliger et al. Although the sensitivity and the specificity are less than those reported by Esliger et al., they are generally in the same range as those reported for waist-worn, uniaxial accelerometer cut points.

A 10-month physical activity intervention improves body composition in young black boys.

Objective. To determine if a 10-month after-school physical activity (PA) intervention could prevent deleterious changes in body composition and cardiovascular (CV) fitness in young black boys. Methods. Following baseline measures, 106 boys (8–12 yrs) were randomized to either a control group or an intervention group, further divided into attenders (ATT) and nonattenders (NATT), participating in ≥60% or <60% of the intervention, respectively. The daily intervention consisted of skills development (25 min), vigorous PA (VPA, 35 min), and strengthening/stretching (20 min) components. Body composition was measured by dual-energy X-ray absorptiometry. Results. Following the intervention, the ATT exhibited an increase in moderate-to-vigorous PA and a significant reduction in BMI, fat mass, and %BF compared to the control group. A significant association among the intervention energy expenditure and changes in body composition and CV fitness was observed only in the ATT group. Conclusion. An after-school PA program of sufficient length and intensity can promote healthy changes in body composition and fitness levels in black boys who attend at least 3 days/week.

Energy Expenditure and Enjoyment of Common Children's Games in a Simulated Free-Play Environment

OBJECTIVE To measure the energy expenditure and enjoyment of childrens games to be used in developing a school-based intervention for preventing excessive weight gain. STUDY DESIGN Healthy weight (body mass index [BMI] < 85th percentile) and overweight or obese (BMI ≥ 85th percentile) third-grade children (15 boys; 13 girls) were recruited. In a large gymnasium, children performed 10 games randomly selected from 30 games used in previous interventions. Total energy expenditure was measured with a portable metabolic unit and perceived enjoyment was assessed using a 9-point Likert scale of facial expressions. Mean physical activity energy expenditure (PAEE = total energy expenditure minus resting metabolism) and enjoyment of the games were adjusted for sex and BMI classification. PAEE and enjoyment were compared using a repeated-measures ANOVA with sex, BMI classification, and games as main effects. RESULTS The games elicited a moderate intensity effort (mean ± standard deviation = 5.0 ± 1.3 metabolic equivalents, 123 ± 36 kcal/30 min). PAEE was higher for boys than for girls (0.12 ± 0.04 versus 0.11 ± 0.04 kcal/kg/min) and for healthy weight compared with overweight children (0.13 ± 0.04 versus 0.11 ± 0.03 kcal/kg/min). Twenty-two of the 30 games elicited a sufficiently high PAEE (≥ 100 kcal/30 min) and enjoyment (≥ neutral expression) for inclusion in future school-based interventions. CONCLUSIONS Not all childrens games are perceived as enjoyable or resulted in an energy expenditure that was sufficiently high for inclusion in future physical activity interventions to prevent the excess weight gain associated with childhood obesity.