Childhood obesity has reached epidemic proportions in developed countries . In New Zealand (NZ) almost one third (31%) of children aged 5–14 years old are overweight or obese . The causes of obesity are multi-factorial. Research evidence points toward an imbalance between energy intake (food consumed) and energy expenditure (physical activity) . Current lifestyles and environments are thought to discourage regular physical activity and encourage sedentary behaviors in children [4, 5]. In particular, sedentary screen-based behaviors (such as television watching, video game play, and computer use) are thought to displace physical activity and are independently associated with obesity  and other adverse health outcomes such as hypertension . In NZ, television watching is the most popular leisure time activity ; data from multiple sources [2, 9, 10] show that NZ children watch more than two hours of television on average per day. Video game playing is also pervasive. A report from the United Kingdom found that 91% of children played three or more gaming formats (or platforms), with video console games the preferred choice. For 11–16 year old children, 74% played 3–7 times per week, with an average duration of 1.9 hours (per session). Similar results have been reported for 6–10 year olds . This video game usage mirrors that seen in NZ and other countries [12, 13]. A recent review  found a positive association between non-television screen viewing (e.g., video games, computer games) and obesity. Similarly, a positive association was reported between time spent playing screen games and obesity after controlling for television watching.
To date, interventions aimed at decreasing obesity in children have been largely unsuccessful. A recent Cochrane systematic review of trials to prevent obesity  found 22 studies; ten long-term (at least 12 months) and 12 short-term (12 weeks to 12 months) that investigated a variety of single or multifaceted interventions . Of the long-term studies, six combined dietary and physical activity interventions [17–22]. Five of these studies resulted in no difference in overweight status between groups. Two long-term studies used physical activity as the sole intervention [23, 24]. Of these, a multi-media approach appeared to be effective in preventing obesity. Four short-term studies used physical activity as the sole intervention [25–28], and two [25, 28] resulted in minor reductions in overweight status in the intervention group. The other eight short-term studies combined advice on diet and physical activity, but none had a significant impact.
The authors of this review highlighted a number of significant design flaws which marred the majority of studies; 1) being underpowered and/or poorly designed given the complexity of the intervention and outcomes sought; 2) many were short term in duration; and 3) lack of environmental influence that would affect the sustainability of the intervention. Despite these limitations, the authors concluded that strategies to increase physical activity and reduce sedentary behavior may be fruitful in preventing overweight and obesity in schoolchildren and that further well-designed randomized controlled trials are required .
Turning off television has been advocated as a population health strategy [10, 28]. However, television and computer games offer a distraction for children at busy times in a parent's day and thus reducing time spent in such sedentary activities constitutes a major challenge. A novel strategy might be to provide popular active alternatives to displace sedentary activities . A new generation of active video games ('exer-gaming') such as Sony PlayStation® EyeToy™ and Nintendo Wii™ provide the potential to turn a traditionally sedentary behavior into a physically active one. During these games, players interact physically (using arm, leg, or whole-body movement) with images onscreen in a variety of activities such as sports (e.g., football, boxing, martial arts) and other activities (dancing, washing windows etc). Games are dependent on player movement, and this active component replaces the largely sedentary hand controller of traditional video games whereby button pushing is used to control the game.
Numerous research studies have been conducted to quantify the energy cost of active video games. Without exception, playing active video games have been shown to elicit greater energy expenditure compared to rest and traditional non-active video games, as well as other common sedentary activities such as TV watching [30–32]. Overall, the energy expenditure associated with playing these active video games is similar in intensity to traditional physical activities such as walking, jogging, and cycling, approximately 3–6 Metabolic Equivalents (METS), which are multiples of resting metabolic rate. Recently, active video games have been considered in intervention research. Four small (n ranged from 15–60), short-term studies [33–36] have been conducted, of which three reported improvements in physical activity level among children over periods of 4–12 weeks. The fourth study  found no effect on physical activity. All studies were of short duration (12 weeks maximum) and thus were unable to provide insight into the sustainability of this intervention and the possible impact on other important variables such as body mass and physical fitness.
Taken together, these findings indicate that active video games are a promising and novel approach to promote physical activity in children. A large, methodologically sound randomized controlled intervention trial is required to determine definitively the long-term effect of active video games on children's physical activity and other outcomes. This paper describes the design and conduct of the eGAME (Electronic Games to Aid Motivation to Exercise) study, which will determine the effects of an active video game intervention over six months on: body mass index (BMI), body weight, percentage body fat, waist circumference, cardio-respiratory fitness, and physical activity levels in overweight NZ children. It was hypothesized that playing 30 minutes of active video games per day over a 6 month period could improve body composition, cardio-respiratory fitness, and physical activity levels in overweight children.