For some patients with morbid obesity surgical interventions, like for example the gastric bypass (Roux-en-Y Gastric Bypass or RYGB), are the only chance to sustainably loose enough weight. The RYGB is the so-called gold standard. In about 70 percent of the patients the gastric bypass operation leads to an improvement of the sugar (glucose) metabolism after the surgery - independently from the weight reduction. It is yet unknown in what way exercise after the intervention supports the positive change in glucose metabolism. Therefore, this study examines the effects of a supervised sports program and whether there are different results in a strength- or in an endurance-training program compared to a control group with normal activity.