Childhood obesity is regarded as one of the most serious public health challenges of the twenty-first century [2, 3]. The issue is global, steadily affecting many low- and middle-income countries, particularly in urban settings [2]. Childhood obesity constitutes something of a public health time bomb, with overweight or obese preschoolers are five times as likely to become overweight or obese adults, compared with their normal-weight peers [4]. Reflecting its status as the world’s second most obese populous country [5], the United States has high rates of obesity among preschool children—approximately one child in eight aged 2–5 years is obese, with particularly high rates in the State of California [4]. Tackling childhood obesity requires a broad range of population-level actions, including the adoption of community-based interventions [6], and there is a need to build the evidence-base around engaging overweight children in cost-efficient, feasible, and effective ways.

Increasing participation in team sports may have a role to play in achieving positive lifestyle changes among this target group, as there is evidence that children who take part in team sports are generally more physically active and have greater levels of physical fitness compared with children who do not [7–10]. Barriers to obese children accessing team sports activities can include parents’ concerns about the safety of outdoor play [11] and the influence of children’s perceptions of their own competence on participation [12]. Also, it is has been shown that children who are overweight perceive more barriers to participating in physical activity compared with normal-weight children [13, 14]. Increasing team sports participation among overweight children, therefore, requires an approach which can successfully address these issues.

The purpose of the project was to design an organized after-school team sports intervention for low-income overweight children and test its effectiveness against a “control” intervention using standard health promotion materials and activities produced by federal health agencies and national nongovernmental health organizations.

The intervention was designed to create a supportive environment, with the aims of reducing weight gain, increasing physical activity and improving psychological health.

Researchers and physicians at Lucile Packard Children’s Hospital and the Stanford University School of Medicine in California, USA devised the Stanford Sports to Prevent Obesity Randomized Trial, or SPORT, after noticing increasing numbers of obese, physically inactive children attending their clinics. It became apparent that simply promoting the benefits of exercise was insufficient to achieve meaningful behavior. While the children and their families tended to recognize the importance of exercise for controlling weight gain, they were unsuccessful in finding ways to routinely incorporate sufficient increased physical activity into their lives. In response to this problem, the SPORT project was conceived, involving designing an after-school physical activity intervention specifically for overweight and obese children and conducting a pilot study to test its efficacy against a traditional nutrition and health education intervention.

Through a combination of feedback from overweight children attending local clinics, school district personnel and staff from other community youth programs, and previous clinical work with children in the community, it was ascertained that soccer was the most popular sport among children in the community. As soccer was also felt to be easy to teach to children with varying levels of skill and experience, it was decided to use co-ed soccer as the basis for designing the intervention. The study was approved by the Stanford University Panel on Protection of Human Subjects in Medical Research and implemented in local schools in collaboration with school district personnel. Initially, a 3-month feasibility study was undertaken with 13 children to establish that it was acceptable to the target group, practical to deliver, and showed promise in slowing BMI gain and improving psychological outcomes before commencing the main pilot study.

The recruitment of participants, delivery of the intervention, and follow-up took place between April 2005, and February 2006.

To be eligible for inclusion, children had to have a body mass index (BMI) score at or above the 85th percentile for age and sex,¹ and be in grades 4 and 5 (ages 9–11) in a low-income community in northern California. Children were excluded from the study if their growth was affected either by a medical condition or any medication they were taking, or if they had a medical condition which would limit their ability to participate in the intervention or the assessments. Children were also required to be given medical clearance to take part in the sport activity by a primary care professional.

Eligible participants were recruited through primary care, schools, and community centers where children were sent home with leaflets describing the study and inviting parents to telephone the study coordinator if they were interested in their child becoming a participant. Recruitment also took place through physician referrals, with doctors issued with “prescription pads” for the study which served as both a referral and medical clearance.

Baseline assessments were completed for all participants before they were randomly allocated either to the after-school soccer intervention or to a traditional nutrition and health education program which served as a control. Twenty-one children were enrolled in the study in total, of whom 14 had never previously participated on a sports team. Nine children were allocated to the treatment intervention and 12 to the control group.

Both the intervention and the control programs were delivered after-school by undergraduate and medical students from Stanford University, under the guidance of the investigators leading the study. All the students underwent appropriate training, including certification in the Protection of Human Research Subjects and training in youth development, group management, and the soccer curriculum for the program.