Obesity in childhood already affects 17% of all children and adolescents in the United States. The prevalence of childhood obesity is still increasing in most of the countries of the world. For example, in the last ten years the prevalence of childhood obesity in Germany increased by 50%. Similar data can be found in Austria. Obesity is a major risk factor for the development of varus/valgus deformities of the knee joint in children. Malalignment in the knee joint combined with increased excess mass, as present in obese children, can result in increased joint stress and damage to articular cartilage. Studies indicate that overweight children encounter a serious risk of either developing unfavourable gait patterns to minimise or maintain joint loadings during walking and have an increased risk for greater hip and knee joint loadings during locomotion. These kinematic and kinetic alterations may lead to an increased risk of developing osteoarthritis over time. Hence, preventing these kinematic or kinetic alterations in obese children might be a possibility to reduce the risk of developing osteoarthritis in adulthood. Recently it was shown, that a lower-extremity strengthening programme could decrease frontal plane moments during walking in adults with knee osteoarthritis. However, to our knowledge there exist no studies examining the preventive effect of those interventions in reducing joint loads in obese children. Therefore, the aims of this study are to examine if a training programme for obese children including strength and neuromuscular exercises can positively affect lower-extremity joint loads during walking and stair climbing. Further we want to determine if this programme can positively change knee related ratings in well being, pain and joint function. A total of 48 obese boys and girls aged between 10 and 18 years with a body mass index exceeding the 97th percentile will be recruited for this study and randomly assigned to an intervention and control group. Participants of the intervention group will undergo a 12 week neuromuscular and quadriceps/hip strengthening program. 3D gait analysis during level walking and stair climbing will be performed at baseline and follow-up. Repeated measures analysis of covariance will be used to compare both groups in biomechanical and clinical outcome parameters. This project will be the basis for an interdisciplinary, competitive research group, binding together sport scientists (biomechanics and informatics) and the field of physiotherapy (clinical knowhow) in Austria. This research group will position the St. Poelten University of Applied Sciences and the Centre of Sports Science in the field of clinical biomechanical research. Research participants and future members of the research group will profit from this collaboration in equal measures. In addition, both fields of research will benefit from the exchange of professional expertise (clinical and biomechanical knowhow) allowing for ongoing cutting-edge investigations in Austrian physiotherapy research as well as Austrian clinical biomechanics science at a high international level. This project is funded by the NFB (NÖ Forschungs- und Bildungsges.m.b.H.).