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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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Gregory J. Welk, Kherrin Wood and Gina Morss

This study examined the utility of a model to explain parental influence on children’s physical activity. Children (n = 994) from 3 elementary schools completed a survey with scales assessing physical activity, attraction to activity, perceived competence, and perceived parental influence. Self-report data on the physical activity levels of parents (n = 536) were also obtained to test the hypothesis that active parents may provide more encouragement and support for their children. The parental influence scales accounted for 20%, 26%, and 28% of the variance in physical activity, attraction to physical activity, and perceptions of competence, respectively. Correlations between parent and child levels of activity were low, but children of active parents had higher scores on the parental influence measures and psychosocial correlates than inactive parents. This study provides further confirmation of the important influence that parents exert on their child’s physical activity behavior.

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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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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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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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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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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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Gregory J. Welk, Charles B. Corbin and Lisa A. Lewis

The Physical Self-Perception Profile (3) assesses perceptions of sport competence, physical conditioning, strength, and body attractiveness. Originally validated with college students, the profile has subsequently been adapted for use with younger children (13) and older adults (2) but not with teenage or athletic populations. The purpose of this study was to evaluate the factor validity of the children’s version of the Physical Self-Perception Profile (C-PSPP) for high school athletes (N = 542). The C-PSPP was given to athletes (both boys and girls) from a variety of competitive sports. The internal reliability of the subscales was good for both sexes (alphas = .73 to .83), with the exception of the Sport scale for the males (alpha = .64). A clear four-factor structure was evident, though cross loadings existed for males on the Sport scale. Results indicate that teenage athletes have strong physical self-perceptions compared to other populations, particularly regarding skill performance and conditioning.