Primary care centres are a key setting to treat people with overweight and moderate obesity. There is growing evidence that sitting for a long time is negatively associated with people's health. Interventions with the aim of reducing daily time of sedentary activities can be an effective strategy to increase daily energy expenditure. To improve the effectiveness of programmes promoting physical activity in primary care we need some clear action protocols that can be easily integrated in the daily routines of primary care professionals.

Objective. The objective of the study is to evaluate the effectiveness of a six-moth primary care intervention to reduce diary hours of sitting time in overweight and obese sedentary patients, as well as to increase their weekly caloric spend.

Methods. The design of the study is a simple randomized controlled trial. Ten primary care centers will be invited to participate and will be randomized into control (CG) and intervention group (IG). Each professional will randomly invite to participate voluntarily moderate obese or overweight patients (BMI: 25-34,9 kg/m2) of both sexes, aged between 25 and 65 years old, who are 6 or more than 6 hours daily sitting. A total of 400 subjects (200 individuals in each group) are needed. In addition, 50 subjects with fibromyalgia will be included in the study to know the feasibility of the intervention among them.

The main dependent variable (sitting times) will be measured with an ActivPAL during first and last intervention week. There will be a follow up after 3, 6 and 12 months of the end of the intervention. Other variables included in the study: number of steps walked, subjective level of physical activity, weight, height, BMI, skinfolds, waist circumference, triglycerides, total cholesterol, (LDL and HDL), glucose, sociodemographic variables, blood pressure and quality of life related to health. A descriptive analysis of all variables and a multivariate analysis to assess differences among intervention and control group will be undertaken. Multivariate analysis will be carried out to assess time changes of dependent variables. All the analysis will be done under the intention to treat principle.

The intervention will be based on a recommendation to find alternatives to progressively substitute Sitting time by doing the regular activities standing or walking. Control group will receive minimum advice.

Inclusion Criteria:

• Overweight and moderate obese patients (BMI: 25-34,9 kg/m2).
• Be 6 or more than 6 hours daily sitting.
• Able to walk and stand up from a chair unaided.
• Subjects who can guarantee a year continuity in the study.

Exclusion Criteria:

• Recommended contradictions to advising physical activity to overweight and obese people.
• Have an obesity surgical operation.