Pediatric Weight Management

Pediatrics and Physical Activity

Citation:

Levin S, Lowry R, Brown DR, Dietz, WH. Physical activity and body mass index among US adolescents. Archives of Pediatric and Adolescent Medicine. 2003; 157: 816-820.

PubMed ID: 12912789
 
Study Design:
Cross-Sectional Study
Class:
D - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:

To determine whether an association would be found between physical activity and weight status among a nationally representative sample of high school students.

Inclusion Criteria:

Three-stage cluster sampling procedure was used to produce a nationally representative sample of 9th through 12th grade students in public and private schools in the 50 states and the District of Columbia.

Exclusion Criteria:
  • Participants with a recorded BMI of less than 11kg per m2 or greater than 55kg per m2 
  • Students with missing data for ethnicity, grade level or any of the physical activity (PA) measures.
Description of Study Protocol:

Data from 1999 Youth Risk Behavior Surveillance System (YRBS) were used in the analyses.

Statistical Analyses

  • Weighted percentages of students classified as active by the five indicators were calculated and compared between demographic subgroups 
  • Multiple logistic regression was performed to obtain adjusted odds ratios and 95% confidence intervals using one physical activity variable at a time as the DV and weight status as the IV
  • Crude odds ratios were used to examine associations between weight status of youth and variables of interest
  • Multiple logistic regression models were calculated to examine the relationship of the independent variables with weight status.
Data Collection Summary:

Dependent Variables

  • BMI was the outcome
  • Participants were categorized as:
    • Underweight (5th to 15th percentile)
    • Normal weight (15th to 85th percentile)
    • At risk for overweight (85th to 95th percentile)
    • Overweight (greater than 95th percentile).

Independent Variables

Physical activity assessed with five different single questions:

  • Vigorous activity: “On how many of the past seven days did you exercise or participate in physical activity for at least 20 minutes that made you sweat and breath hard?”
  • Moderate activity: “On how many of the past seven days did you participate in physical activity for at least 30 minutes that did not make you sweat or breathe hard?”
  • Strength activity: “On how many of the past seven days did you do exercises to strengthen or tone your muscles, such as push-ups, sit-ups or weight lifting?”
  • Sports: “During the past 12 months, on how many sports teams did you play?”
  • Physical education: “In an average week when you are in school, on how many days do you go to physical education (PE) class?”
    • Less than tjree = inactive group
    • Three or more = active group
    • Less than five = inactive group
    • Five or more = active group
    • Less than three = inactive group
    • Three or more = active group
    • 0 = inactive group
    • One plus = active group
    • 0 = inactive group
    • One plus= active group.

 

Description of Actual Data Sample:

Sample included 13,295 students in grades nine to 12.

Summary of Results:
  • 78% of the students were classified as active on at least one of the physical activity (PA) measures, 12% were not sufficiently active by any measure and 9% were classified as active on all criteria
  • Participation in physical education declined with each increasing grade level
  • Participation in vigorous PA, strength and sports teams also declined with age and grade.

Physical Activity and Overweight

  • Participation in vigorous activity was associated with a 13 to 15% reduction in the likelihood of overweight, but the values were not significant for boys or girls
  • Participation in moderate activity was associated with a 25% reduction in the likelihood of overweight. The risk was significant for boys; OR 0.75 (0.61 to 0.93), but not for girls OR 0.76 (0.48 to 1.18).
  • Participation in a sports team was associated with a reduced risk of overweight; OR 0.62 (0.50 to 0.78) and a reduced overweight prevalence; OR 0.63 (0.48 to 0.85) for girls but the associations were not significant for boys.
  • Physical education participation was not associated with risk for overweight or overweight status in boys or girls.
Author Conclusion:

Weight status among high school students is correlated with selected physical activity behaviors, especially among adolescent boys.

Funding Source:
Government: National Center for Chronic Disease Prevention and Health Promotion, Centers for Disease Control and Prevention
Reviewer Comments:
  • The categorization of activities may reduce the likelihood of seeing associations
  • Stronger effects would be seen if multiple categories were used in the analyses.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) No
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? No
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? N/A
  8.6. Was clinical significance as well as statistical significance reported? N/A
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes