Moderating influences of baseline activity levels in school physical activity programming for children: the Ready for Recess project

Abstract

Background: A limitation of traditional outcome studies from behavioral interventions is the lack of attention given to evaluating the influence of moderating variables. This study examined possible moderation effect of baseline activity levels on physical activity change as a result of the Ready for Recess intervention.

Methods: Ready for Recess (August 2009-September 2010) was a controlled trial with twelve schools randomly assigned to one of four conditions: control group, staff supervision, equipment availability, and the combination of staff supervision and equipment availability. A total of 393 children (181 boys and 212 girls) from grades 3 through 6 (8-11 years old) were asked to wear an Actigraph monitor during school time on 4-5 days of the week. Assessments were conducted at baseline (before intervention) and post intervention (after intervention).

Results: Initial MVPA moderated the effect of Staff supervision (β = -0.47%; p < .05), but not Equipment alone and Staff + Equipment (p > .05). Participants in the Staff condition that were 1 standard deviation (SD) below the mean for baseline MVPA (classified as "low active") had lower MVPA levels at post-intervention when compared with their low active peers in the control condition (Mean diff = -10.8 ± 2.9%; p = .005). High active individuals (+1SD above the mean) in the Equipment treatment also had lower MVPA values at post-intervention when compared with their highly active peers in the control group (Mean diff = -9.5 ± 2.9%; p = .009).

Conclusions: These results indicate that changes in MVPA levels at post-intervention were reduced in highly active participants when recess staff supervision was provided. In this study, initial MVPA moderated the effect of Staff supervision on children's MVPA after 6 months of intervention. Staff training should include how to work with inactive youth but also how to assure that active children remain active.

Figure 1

Percent time spent in MVPA at recess for a (randomly selected) subgroup of 25 individuals. Each line represents an individual. This figure illustrates a high degree of variability in individual’s baseline scores (intercept) and change over time (slopes). This justifies the need for a random intercept term at level-2 (individual).

Figure 2

Percent time spent in MVPA at recess for the 12 schools. Each line represents a school. Similarly to Figure 1, there was a significant difference in baseline scores for school clusters, and therefore, justifying the need for random intercepts at this level.

Figure 3

Average MVPA scores for the control and each treatment group. Both the Staff (ST) and the Equipment (EQ) treatments had a negative effect on individuals’ MVPA. The Staff + Equipment (STEQ) treatment effect was positive.

Figure 4

Average % MVPA difference among Low, Moderate, and High active groups, per treatment group. Each activity level subgroup was compared with their respective control group (e.g. % MVPA Difference Low Staff = “Low Staff”- “Low Control” at trial 2, holding constant all the remaining variables in the full model). There was a reduced effect trend (from Low to High active individuals) for the Staff (ST), and the Staff + Equipment (STEQ) treatment groups. This trend was reversed in the Equipment (EQ) group (the effect was higher for High active individuals and decreased among Moderate, and Low active subgroups). *Significantly different than respective control group at trial 2 (p < .01). ^#Borderline significantly different than respective control group at trial 2 (.01 < p < .05).