The purpose of this study is to implement a peer modeling intervention to improve self-efficacy and aerobic fitness in obese youth. A total of 40 obese (defined as Body Mass Index greater than the 95th percentile for age and gender) youth will participate in this study.

There has been a dramatic increase in the prevalence of overweight and obese children in all regions of Canada. In fact, Canada has one of the highest rates of childhood obesity compared to other developed countries. This is disconcerting because this preventative condition is strongly associated with the risk of future disease, such as adult obesity, insulin resistance, type 2 diabetes, cardiovascular problems and psychosocial distress. This trend is a driving factor to develop effective strategies for assessment and intervention.

Aerobic fitness is the ability of the cardiovascular and respiratory system to deliver oxygen to working muscles and utilize that oxygen to produce energy. Aerobic fitness is a strong indicator of physical activity and also correlates with the aforementioned diseases. It is measured as peak ventilatory oxygen (peak VO2; mL/kg min), and is evaluated using a maximal incremental exercise protocol on a treadmill, whereby expired gases are analyzed using a metabolic cart. Aerobic fitness values are inconsistent in youth, particularly obese youth. This discrepancy is due to low self-efficacy. Self-efficacy refers to the belief that one has the power and capabilities to produce an effect. Low self-efficacy is prominent in obese youth because they lack actual and perceived physical competence and social support. This may translate into less effort invested by this population into physical activity, and by the same token, aerobic fitness tests. To date, no experimental studies have attempted to address these psychological variables and apply an intervention to achieve accurate peak VO2 values in obese adolescents.

Peer modelling is the demonstration of particular behaviors that are learned observationally and is a powerful source of self-efficacy. This mode of learning has been very successful in increasing the consumption of new foods (36 subjects) and activity levels (100 subjects) in children. Based on this success, it would suggest that the investigators could confidently apply it to this study. Therefore the main objective is to examine the effect of a modeling intervention (DVD film) on self-efficacy and peak VO2 in obese youth during a maximal treadmill test. Models will demonstrate and articulate increased confidence to perform the test and offer a variety of strategies to cope with the maximal effort and overcome the associated challenges during the test (e.g. shortness of breath, sweating, and increased heart rate). The models will not be participants in the study.

Obese (defined as Body Mass Index greater than the 95th percentile for age and gender) youth (10-17 years, N = 40) who receive written consent from a parent or guardian will be asked to participate in the study. Prior to undertaking the aerobic fitness test, children are required to seek approval from their family physician by completing the Physical Activity Readiness Questionnaire (PAR-Q).

Participants will be randomized after baseline measures are completed into one of two conditions: peer modeling intervention or control to ensure group equivalency. Following randomization, participants in the intervention group will watch the peer modeling DVD film in the lab. Those in the control group will view a DVD film of similar length about nutrition. After seven days, participants in both groups will return for follow-up. One week is a suitable interval because it provides time for participants to reflect on any information they received from the DVD films and minimize external confounding factors, while not providing enough time to see changes in fitness (which requires approximately 3 months). Prior to the second exercise test, participants will watch the DVD film they viewed the previous week. Afterwards, participants will complete their peak VO2 test and self-reported measures. All participants will be asked not to change their normal physical activity patterns during the week.

To complete a peak VO2 test, participants will be required to complete a maximal incremental exercise protocol on a treadmill. The test will be conducted by trained personnel and terminated when participants are unable to continue the protocol, or when their vital signs warranted discontinuation.

The results of this RCT will provide an accurate measurement of aerobic fitness, which is crucial to assessing health status, risk of disease and assisting in planning programs aimed at improving quality of life in adolescents.

Inclusion Criteria:

• Children and adolescents aged 10-17 years who are obese, defined as Body Mass Index greater than the 95th percentile for age and gender

Exclusion Criteria:

• Participants who smoke, are pregnant or have an illness or disease will be excluded from the study.