Physical exercise decreases the risk of obesity, diabetes mellitus, and cardiovascular disease. Skeletal muscle can be exercised by two ways: Concentric contraction is defined as active shortening of muscles, e.g. by stepping upwards, whereas eccentric muscle contraction is defined as active resistance to stretching, e.g. by stepping downwards. Although the effects of exercise (i.e. the combination of concentric and eccentric muscle contraction) on metabolic parameters have been extensively investigated, there are no data on the specific metabolic effects of concentric versus those of eccentric muscle work in humans.