In the developing countries, obesity prevalence is on a dramatic rise. Obesity is related to co-morbidities and as a result, obesity significantly shortens life expectancy and lowers quality of life. To prevent this, participation in exercise or training programs is absolutely necessary, in order to generate adipose tissue mass loss. The amount of adipose tissue mass loss is, amongst others, dependent on lipolysis which is under endocrine regulation by, mainly, catecholamines, insulin and atrial natriuretic peptide. However, large variations in adipose tissue mass loss and gain are likely in obese subjects, possibly due to a decreased lipolytic effect of these hormones (as was shown for catecholamines in the subcutaneous adipose tissue of obese subjects). However, the relative contribution of atrial natriuretic peptide in the lipolytic process remains elusive, particularly in subjects with obesity, which show an increased plasma expression of atrial natriuretic peptide.

The aim of the present study is to observe the contribution of atrial natriuretic peptide in the subcutaneous adipose tissue of obese subjects. This will be tested by measurements of extracellular glycerol levels (by microdialysis) in the subcutaneous adipose tissue in situ at rest and during endurance exercise under local beta- and alpha-blockade.

Eventually, the knowledge gained from this research will contribute to the optimization of exercise programs for people with obesity.

Inclusion Criteria:

• Obese group: BMI > 30 kg/m², sedentary (no regular physical activity last 6 months), insulin sensitive or insulin resistant
• Lean controls: BMI > 18.5 kg/m² and < 25 kg/m², regular physical activity, insulin sensitive

Exclusion Criteria:

• Regular glucose lowering medication or beta blockade medication
• Presence of chronical diseases
• Orthopedic or neurological problems

subjects with obesity