Meta-analysis of Anthropometric Outcomes of Supervised Exercise Interventions in Healthy Adults

Vicki Conn PhD RN FAAN

Todd Ruppar PhD RN

Lorraine Phillips PhD RN

Jo-Ana Chase MSN RNMETA-ANALYSIS RESEARCH CENTER

UNIVERSITY OF MISSOURI SCHOOL OF NURSING

Parent Study: Meta-Analysis of Physical Activity Interventions in Healthy People

Funding: Meta-analysis of interventions to increase exercise & physical activity (R01NR07870)

Vicki Conn, principal investigator

Grant co-investigators:Adam Hafdahl PhDDavid Mehr MD MSDiane Johnson MS

Extant Research• Evidence mixed about effects of PA on

anthropometric outcomes

• Limited previous meta-analyses:

• Focused on clinical populations

• Did not report findings separately for exercise and diet changes

• Did not separate supervised exercise and motivational interventions

• 1991 last semi-comprehensive meta-analysis

• No previous moderator analyses

What is the overall effect of supervised exercise interventions on anthropometric outcomes?

How do the anthropometric effects of supervised exercise vary depending on sample, design, or intervention characteristics?

Research Questions

Inclusion Criteria• ‘Healthy’ adult sample• Samples included regardless of anthropometric

status at entry• Supervised exercise with verified exercise dose• Adequate data to calculate effect size for body

mass index (BMI), weight, percent body fat, or central obesity (abdominal girth, waist-to-hip ratio)

Search Strategies (1)• Searched 14 computerized databases

– MEDLINE & PsycINFO– EMBASE– Cochrane Controlled Trials Register– Database of Abstracts of Reviews of Effectiveness – Healthstar– Combined Health Information Database

– Educational Resources Information Center – Sport Discus– Dissertation Abstracts International

Search Strategies (2)

• Ancestry searches

• Author searches from all primary studies

• Hand searches of 114 journals

• Conference abstracts (e.g. ACSM, APHA, AHA, MNRS, SBM)

• Research registers (e.g. CRISP [RePORT])

• Reviewed 54,642 studies for potential eligibility

Coding Data Categories• Source characteristics

• Published vs. unpublished• Year of distribution

• Participant attributes• Ages• Gender/minority distribution

• Methodological features • Supervised exercise intervention

characteristics• Effect size information

Calculating Effect Sizes

Analyses• Random effect model

• Assumes heterogeneity beyond sampling error• Appropriate with variations in research methods

(interventions, measures, samples)

• Effect sizes weighted by inverse of variance• Effect sizes adjusted for bias• Q & I2 statistics to examine heterogeneity• Moderator analyses:

• Dichotomous: meta-analysis analogue of ANOVA• Continuous: meta-analysis analog of regression

Study Characteristics

• Two-group comparisons: treatment vs. control • 316 comparisons• 24,689 people

• Single-group comparisons: treatment baseline vs. treatment outcome • 794 comparisons• 20,335 people

Sample Characteristics

• Sample sizes:

• Two group: median 23 subjects

• Single group: median 17 subjects

• Modest attrition: median 7%

• Age: median 38 years

• Percent female: median 55%

• Percent minority: median 13% (poorly reported)

• Baseline BMI: median 27 – 28 kg/m2

Typical Intervention Characteristics

Supervised exercise interventions:

• 47 minutes per session

• 3 sessions per week

• 42 total sessions

Anthropometric Outcomes

Comparisons k ES p I2

Treatment vs. control post-intervention 316 .21 <.001 .29

Treatment vs. control pre-post 303 .18 <.001 0

Treatment pre- vs. post-intervention 794 .20 <.001 .51

Control group pre- vs. post-intervention 226 -.03 <.001 0

k = number of comparisonsES = effect size (d index)p = test of statistical significance of effect sizeI2 = index of heterogeneity beyond within-study sampling error

Effect Size Meaning• Converted effect size (treatment vs. control at outcome)

to original metric of BMI

• Effect size * BMI SD = difference in original metric (.21 * 4.6 =.97)

• At outcome:• Treatment subjects BMI = 27.0

• Control subjects BMI = 28.0

• Mean difference 2.3 kg between treatment and control subjects

Significant Moderators• Previous exercise: studies of people with existing exercise behavior

reported lower ES (.11) than studies of sedentary subjects (ES = .24)

• Lower effect size for studies with more minority subjects (B = -.26)

• Larger exercise dose associated with better anthropometric outcomes:

• Studies with more total number of exercise sessions reported larger effect sizes (B = .29): remained important in multivariate analyses

• Studies with more total minutes of supervised exercise reported larger effect sizes (B = .29): total number of exercise sessions more important

Potential Moderators Which Were Not Significant

• Publication year

• Published vs. unpublished report

• Presence of funding

• Sample characteristics: gender, age, BMI

• Random vs. non-random assignment

• Behavioral target (exclusively PA vs. PA plus diet)

• Fitness testing present vs. absent

• Aerobic exercise only vs. aerobic plus resistance

• Individual components of exercise dose:• Minutes of exercise per session

• Frequency of sessions per week

Limitations• Primary studies often poorly report

interventions, minority participants, and statistical outcomes

• Anthropometric outcomes may have measurement error

• Need research with documented exercise dose over years to determine health outcomes

• Future meta-analyses focus on overweight/obese adults

Discussion• Clinically important improvement in BMI following

interventions (BMI = 28 vs. 27; Kg = 2.3 difference)

• Important health benefit across years of exercise

• Exercise may be more effective in preventing gain

• Exercise confers benefits beyond anthropometric outcomes

• Minority subjects may experience less improvement

• Dose matters: total number of sessions most important (but few studies with brief or infrequent sessions)