Regular exercise has several positive health effects including increased physical fitness and muscle mass. It is well known that increased muscle mass is associated with increased resting energy expenditure which may facilitate weight loss and maintenance. Previous studies have, however, failed to show any consistent association between the intensity of physical exercise and energy expenditure, or relate the variance in these adaptations to genetic variability. Whether high-intensity exercise (HIE) is associated with improved health related quality of life in severely obese patients remains unknown.