BACKGROUND
The promotion of physical activity to school age children is a public health priority. There is a need to identify suitable contexts to enhance daily physical activity opportunities for children (Strong et al., 1998). Recess represents a school-based daily activity opportunity for children to be physically active. Previous studies have investigated the short-term effects of playground markings on children’s recess physical activity levels (Stratton & Mullan, 2005); however, the longer-term effects are not widely reported.

OBJECTIVE
The objective of the study was to determine the effects of a playground intervention on children’s recess moderate-to-vigorous (MVPA) and vigorous physical activity (VPA) engagement over time.

METHODS
Two hundred and ninety-eight children (149 boys, 149 girls) from 26 elementary schools participated in the study. Fifteen schools each received £20,000 through a national £10 million Sporting Playgrounds Initiative to redesign the school playground environment based on the sporting playground Zoneparc design. Eleven schools served as socioeconomic matched controls. Physical activity during recess was quantified using a uni-axial accelerometer prior to, 6 weeks and 6 months following the playgrounds being painted with multicolor playground markings. Control schools received no markings through the study. The accelerometer epoch length was set at 5 seconds. The percentage of time spent engaged in MVPA and VPA during recess at each measurement point was determined using existing thresholds. Multilevel analysis was used to determine the effects of the intervention across time using a three level structure. The levels were time of follow-up measure (level 1), pupil (level 2) and school (level 3). MVPA and VPA following the intervention were the outcome variables. Baseline MVPA and VPA, body mass index, age, recess time and gender were identified as potential covariates. Intervention effects were analyzed using adjusted models where covariates were added to the model. An intervention x time interaction term was also constructed to investigate potential changes in the intervention effect between 6 weeks and 6 months post-intervention. Separate analyses were conducted for MVPA and VPA.

RESULTS
A statistically positive intervention effect across time was found for both MVPA (p = 0.03) and VPA (p = 0.01). Children in the intervention schools engaged in 4.5% (95%CI: 0.59 to 8.47) and 2.3% (95%CI: 0.71 to 3.93) more MVPA and VPA respectively during recess than control school children. A significant positive intervention x time interaction was found for VPA (p = 0.05), indicating that the intervention effect strengthened longitudinally across time. The intervention x time interaction term was not significant for MVPA (p = 0.56).

CONCLUSIONS
The results indicate that developing school playgrounds based on the Zoneparc design is a suitable school based for increasing children’s recess MVPA and VPA over time. Increases in recess MVPA were sustained across time, whilst the intervention effect was stronger at 6 months for VPA. It has been suggested that children are less active in restricted environments (Pellegrini & Smith, 1993). The increases observed in VPA may be attributable to increased play space due to the zonal design. Overall, the results indicate that playground markings and physical structures are an effective method for significantly increasing children’s recess physical activity levels in the longer-term.