The purpose of this study is to examine the effects of aerobic eccentric training in overweight and obese children.

recent studies have shown that similarly to regular exercise, aerobic ECcentric Contraction (ECC) exercise induces changes in the musculoskeletal system while using lower energy consumption, due to the fact that eccentric training creates greater force in the muscle.

most of the studies in this subject were done on healthy or overweight adults. therefore, the effect of aerobic eccentric training on children is still unknown. this study wants to test the impact of eccentric training on overweight and obese children.

this study will include approximately 100 overweight and obese children (boys and girls), aged 5-18 years. participants will be recruited from the population of overweight children from children sports medical center 'Meir' in Kfar Saba, Israel. participants will be randomly divided into two groups (intervention and control). Participants and their parents will sign a consent form before entering the study.

Each participant will undergo a series of tests including: anthropometrics (height, weight, bmi, body composition by BIA), fitness tests (Maximal distance achieved in a 12min outdoor run\walk, Vertical jump, Standing long jump, 4X10 meter sprint run), quadriceps and hamstrings strength test (hand-held dynamometer MicroFet2), bone strength (bone sonometer), ankle and tibial kinematic(accelerometers+ video of foot strike).

Intervention group will then perform an 8 week (16 sessions) ECC training program on a decline treadmill, the program will include two weeks of habituation to lower as possible DOMS (delayed onset muscle soreness) and possible injuries, training length and intensity will be gradually increasing over the time of the program, maximal negative gradient will be -15% at the end of the program.

Control group will perform the same amount of training (volume, intensity and frequency) on a neutral gradient surface. After completing the training program each participant will perform again the series of tests. Once all the data is collected, statistical test will be performed in order to learn about the effect of ECC training program on overweight and obese children.

Inclusion Criteria:

• Children and adolescents aged 5-18.
• Children and adolescents with overweight defined as BMI percentile over 85%.
• Children and adolescents who are able to perform moderate physical activity.
• Children and adolescents that participate in 'Meir' hospital sports and health centre.

Exclusion Criteria:

• Participant that does not wish to participate - will not be obligated to do so, and shall not participate in the study.
• Participants with orthopaedic history in the past two years.