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Gregory J. Welk

A major challenge in public health research on physical activity is in reconciling the commonly observed differences between estimates provided by monitor-based methods and report-based methods. Calibration methods are widely used in measurement research to rescale or convert an estimate so that it matches a more robust criterion value. Accelerometry-based activity monitors are routinely calibrated against more robust estimates of indirect calorimetry, but surprisingly little research is done to calibrate report-based estimates. The purpose of the paper was to document the utility of calibration methods for harmonizing estimates from report-based measures to correspond with data from monitor-based methods. While there are also limitations associated with monitor-based methods, this procedure provides a systematic way to promote harmonization of estimates obtained from these different methods. This enables the more feasible report-based measures to provide more accurate group-level estimates of physical activity for different research applications.

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Michelle Ihmels, Gregory J. Welk, James J. McClain and Jodee Schaben

Background:

Advances in BIA offer practical alternative approaches to assessing body composition in young adolescents and have not been studied for comparability.

Methods:

This study compared reliability and convergent validity of three field tests (2-site skinfold, Omron and Tanita BIA devices) on young adolescents. Reliability was determined using intraclass correlation coefficients, convergent validity was examined by computing correlations among the three estimates, differences in estimated body fat values were evaluated using repeated-measures ANOVA, and classification agreement was computed for achieving FITNESSGRAM ® Healthy Fitness Zone.

Results:

ICC values of all three measures exceeded .97. Correlations ranged from .74 to .81 for males and .79 to .91 for females. Classification agreement values ranged from 82.8% to 92.6%.

Conclusions:

Results suggest general agreement among the selected methods of body composition assessments in both boys and girls with the exception that percent body fat in boys by Tanita BIA is significantly lower than skinfold estimation.

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James J. McClain, Gregory J. Welk, Michelle Ihmels and Jodee Schaben

Background:

The PACER test is a valid and reliable assessment of aerobic capacity in children. However, many schools lack adequate space to administer the test. This study compared the utility of the standard 20m PACER test with an alternative 15m PACER protocol in 5th and 8th grade students.

Methods:

A total of 171 students completed both PACER protocols in a counterbalanced design. Agreement between the two protocols was assessed with correlations, repeated-measures ANOVA, and classification agreement into the FITNESSGRAM ® healthy fitness zones.

Results:

The difference in estimated VO2max between the two tests was slightly larger for boys (5th grade, 1.32 ml/kg/min; 8th grade, 1.72 ml/kg/min) than girls (5th grade, 0.14 ml/kg/min; 8th grade, 1.11 ml/kg/min), but these differences are probably not of practical significance. Classification agreement was 88% for boys and 91% for girls.

Conclusions:

Collectively, the results suggest that the 15m and 20m PACER provide similar information about aerobic fitness in youth. The 20m test is recommended when possible, but the 15m provides a useful alternative for schools with smaller gymnasiums.

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Stuart J. Fairclough, Nicola D. Ridgers and Gregory Welk

Background:

Vigorous-intensity physical activity (VPA) may confer superior health benefits for children compared to moderate-intensity physical activity (MPA), but the correlates of MPA and VPA may differ. The study purpose was to investigate associations between selected enabling, predisposing, and demographic physical activity correlates, and MPA and VPA during weekdays and at weekends.

Methods:

Data were gathered from 175 children (aged 10 to 11 years). MPA and VPA were assessed using accelerometers. Correlates were measured at child and school levels. Multilevel analyses identified correlates that significantly predicted MPA and VPA.

Results:

Gender significantly predicted weekday MPA (P < .001), and weekend MPA (P = .022) and VPA (P = .035). Weekday VPA was predicted by gender (P < .001), indices of multiple deprivation score (P < .003), BMI (P = .018), and school playground area (P = .046).

Conclusions:

Gender was the most significant correlate of MPA and VPA. Children most likely to engage in weekday VPA were boys with lower deprivation scores and BMI values, with access to larger playground areas.

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Eric E. Wickel, Joey C. Eisenmann and Gregory J. Welk

Background:

This study compared physical activity levels among early, average, and late maturing boys and girls.

Methods:

Physical activity was assessed with an Actigraph accelerometer in 161 (76 boys, 85 girls) 9 to 14 year olds over 7 consecutive days. Anthropometric variables were measured and the maturity offset (ie, years from peak height velocity) was predicted. Biological maturity groups (early, average, and late) were created based on the mean estimated age at peak height velocity for boys and girls separately.

Results:

Levels of moderate-to-vigorous physical activity (MVPA) were similar between early, average, and late maturing boys and girls after adjusting for differences in chronological age. Levels of MVPA progressively declined across chronological age in boys and girls (P < .001) and gender differences existed at 10-, 12-, and 13-years, with boys having higher levels than girls (P < .05). When aligned according to biological age, gender-related differences in MVPA did not exist.

Conclusions:

Within this sample of 9 to 14 year old boys and girls, there were no significant differences in MVPA among early, average, and late maturing individuals.

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Kelly R. Laurson, Gregory J. Welk and Joey C. Eisenmann

Background:

The purpose of this study was to provide a practical demonstration of the impact of monitoring frame and metric when assessing pedometer-determined physical activity (PA) in youth.

Methods:

Children (N = 1111) were asked to wear pedometers over a 7-day period during which time worn and steps were recorded each day. Varying data-exclusion criteria were used to demonstrate changes in estimates of PA. Steps were expressed using several metrics and criteria, and construct validity was demonstrated via correlations with adiposity.

Results:

Meaningful fluctuations in average steps per day and percentage meeting PA recommendations were apparent when different criteria were used. Children who wore the pedometer longer appeared more active, with each minute the pedometer was worn each day accounting for an approximate increase of 11 and 8 steps for boys and girls, respectively (P < .05). Using more restrictive exclusion criteria led to stronger correlations between indices of steps per day, steps per minute, steps per leg length, steps per minute per leg length, and obesity.

Conclusion:

Wear time has a meaningful impact on estimates of PA. This should be considered when determining exclusion criteria and making comparisons between studies. Results also suggest that incorporating wear time per day and leg length into the metric may increase validity of PA estimates.

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Jung-Min Lee, Pedro F. Saint-Maurice, Youngwon Kim, Glenn A. Gaesser and Gregory Welk

Background:

The assessment of physical activity (PA) and energy expenditure (EE) in youth is complicated by inherent variability in growth and maturation during childhood and adolescence. This study provides descriptive summaries of the EE of a diverse range of activities in children ages 7 to 13.

Methods:

A sample of 105 7- to 13-year-old children (boys: 57%, girls: 43%, and Age: 9.9 ± 1.9) performed a series of 12 activities from a pool of 24 activities while being monitored with an indirect calorimetry system.

Results:

Across physical activities, averages of VO2 ml·kg·min-1, VO2 L·min-1, EE, and METs ranged from 3.3 to 53.7 ml·kg·min-1, from 0.15 to 3.2 L·min-1, from 0.7 to 15.9 kcal·min-1, 1.5 MET to 7.8 MET, respectively.

Conclusions:

The energy costs of the activities varied by age, sex, and BMI status reinforcing the need to consider adjustments when examining the relative intensity of PA in youth.

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Matthew T. Mahar, Gregory J. Welk, David A. Rowe, Dana J. Crotts and Kerry L. McIver

Background:

The purpose of this study was to develop and cross-validate a regression model to estimate VO2peak from PACER performance in 12- to 14-year-old males and females.

Methods:

A sample of 135 participants had VO2peak measured during a maximal treadmill test and completed the PACER 20-m shuttle run. The sample was randomly split into validation (n = 90) and cross-validation (n = 45) samples. The validation sample was used to develop the regression equation to estimate VO2peak from PACER laps, gender, and body mass.

Results:

The multiple correlation (R) was .66 and standard error of estimate (SEE) was 6.38 ml·kg−1·min−1. Accuracy of the model was confirmed on the cross-validation sample. The regression equation developed on the total sample was: VO2peak = 47.438 + (PACER*0.142) + (Gender[m=1, f=0]*5.134) − (body mass [kg]*0.197), R = .65, SEE = 6.38 ml·kg–1·min–1.

Conclusions:

The model developed in this study was more accurate than the Leger et al. model and allows easy conversion of PACER laps to VO2peak.