This PhD-project is based on a planned randomised controlled study including 50 or more treatment seeking morbidly obese patients who will be randomised to either a 24 week moderate-intensity exercise (MIE) programme or a 24 week high-intensity exercise (HIE) programme. The investigators main hypothesis is that patients randomised to the HIE-program will achieve higher energy expenditure during rest and physical activity after treatment than those allocated to the MIE-programme. In addition, the investigators hypothesise that the HIE-group will achieve a better health related quality of life than the MIE-group after treatment. The investigators also hypothesize that inter-individual variability in adaptation to the two training regimens may be due to genetic factors. If the investigators hypotheses are confirmed, this project might have beneficial clinical implications for future obesity treatment strategies.