Childhood obesity is a public health problem; in Mexican children a high prevalence of cardiovascular risk factors are present. Physical activity has been proposed as a strategy to reduce this risk. We conducted a pre-posttest intervention study of 214 school-aged Mexican children (4th to 6th grade), to assess the effects of two physical activity routines with different duration and intensity (40 minute aerobic routine vs. 20 minute routine) on cardiovascular risk markers. Physical activity routines were assigned randomly to two public schools in Toluca, Mexico (20 min: group 1 (n= 117), 40 min: group 2 (n=97)). The routines were implemented Monday through Friday for 12 weeks. Nutrition assessment was done before and after the intervention and included anthropometric measurements (weight, height, body mass index, waist circumference and body composition), blood pressure and biochemical analysis (triglycerides, total cholesterol LDL-cholesterol, HDL-Cholesterol, glucose and insulin). Heart rate was monitored 3 times during the intervention to evaluate the routine´s intensity.

Inclusion Criteria:

• All children from 4th to 6th grade, from 2 public urban schools in Toluca, Estado de México

Exclusion Criteria:

• If they have a chronic disease
• If they can not do exercise
• If they have low body mass index (BMI less than 5th percentile).
• If they miss more than 20 sessions
• If they decide that they did not want to participate any more.