Opportunities and challenges in physical activity research in young people

Estimated Distributions of Usual Physical Activity during Recess

PURPOSE

This study aimed to estimate distributions of usual physical activity during recess in schools in low-income areas using measurement error models and to compare model-adjusted distributions to unadjusted distributions based on a single day of measurement.

METHODS

A randomized study of the Playworks program was conducted in 29 schools from six U.S. cities. A sample of 365 fourth- and fifth-grade students in 26 of the study schools wore accelerometers during their recess periods on two school days. Estimates for the percentage of time spent in moderate to vigorous physical activity (MVPA) during recess were constructed from the accelerometer data for each school day. Using measurement error models, distributions for the usual amount of time spent in MVPA during recess were estimated for intervention and control groups of males and females. Unadjusted distributions for these same groups were also constructed using data from a single school day.

RESULTS

There is considerable intraindividual variability in the students' physical activity, which accounts for 67%-83% of the overall variability, depending on the study group. Unadjusted single-day distributions are much wider and have more weight in the tails than model-adjusted distributions owing to this large intraindividual variability in the data.

CONCLUSIONS

Using measurement error models to analyze physical activity data collected from recess periods will allow for more accurate and reliable inferences on students' physical activity.

A systematic review of intervention effects on potential mediators of children's physical activity

Background

Many interventions aiming to increase children’s physical activity have been developed and implemented in a variety of settings, and these interventions have previously been reviewed; however the focus of these reviews tends to be on the intervention effects on physical activity outcomes without consideration of the reasons and pathways leading to intervention success or otherwise.

To systematically review the efficacy of physical activity interventions targeting 5-12 year old children on potential mediators and, where possible, to calculate the size of the intervention effect on the potential mediator.

Methods

A systematic search identified intervention studies that reported outcomes on potential mediators of physical activity among 5-12 year old children. Original research articles published between 1985 and April 2012 were reviewed.

Results

Eighteen potential mediators were identified from 31 studies. Positive effects on cognitive/psychological potential mediators were reported in 15 out of 31 studies. Positive effects on social environmental potential mediators were reported in three out of seven studies, and no effects on the physical environment were reported. Although no studies were identified that performed a mediating analysis, 33 positive intervention effects were found on targeted potential mediators (with effect sizes ranging from small to large) and 73% of the time a positive effect on the physical activity outcome was reported.

Conclusions

Many studies have reported null intervention effects on potential mediators of children’s physical activity; however, it is important that intervention studies statistically examine the mediating effects of interventions so the most effective strategies can be implemented in future programs.

Determinants of change in physical activity in children and adolescents: a systematic review

CONTEXT

Data are available on correlates of physical activity in children and adolescents, less is known about the determinants of change. This review aims to systematically review the published evidence regarding determinants of change in physical activity in children and adolescents.

EVIDENCE ACQUISITION

Prospective quantitative studies investigating change in physical activity in children and adolescents aged 4-18 years were identified from seven databases (to November 2010): PubMed, SCOPUS, PsycINFO, Ovid MEDLINE, SPORTDdiscus, Embase, and Web of Knowledge. Study inclusion, quality assessment, and data extraction were independently validated by two researchers. Semi-quantitative results were stratified by age (4-9 years, 10-13 years, and 14-18 years).

EVIDENCE SYNTHESIS

Of the 46 studies that were included, 31 used self-reported physical activity; average methodologic quality was 3.2 (SD=1.2), scored 0-5. Of 62 potential determinants identified, 30 were studied more than three times and 14 reported consistent findings (66% of the reported associations were in the same direction). For children aged 4-9 years, girls reported larger declines than boys. Among those aged 10-13 years, higher levels of previous physical activity and self-efficacy resulted in smaller declines. Among adolescents (aged 14-18 years), higher perceived behavioral control, support for physical activity, and self-efficacy were associated with smaller declines in physical activity.

CONCLUSIONS

Few of the variables studied were consistently associated with changes in physical activity, although some were similar to those identified in cross-sectional studies. The heterogeneity in study samples, exposure and outcome variables, and the reliance on self-reported physical activity limit conclusions and highlight the need for further research to inform development and targeting of interventions.