There has never been as much focus on running as in these days. With the knowledge the investigators have today, there is reason to believe that it is healthy to run both in a physical sense, but perhaps also in terms of brain function. However, there has not previously carried out extensive comparative studies of very active runners and healthy untrained control subjects. In this project the investigators will characterize the degree of training in subjects as the investigators will carry out various forms of physiological studies on the subjects' fitness level. The investigators will examine whether there is a linkage between training level and brain function.