The investigators wish to compare very active runners in healthy untrained control subjects on a number of parameters.

The project aims to understand the underlying mechanisms by which physical inactivity causes diseases. This the investigators will study the full spectrum of physical activity, from the most inert of the most active people. The investigators have already collected muscle biopsies and established stem cells from people with Type 2 diabetes, obese healthy and normal weight healthy. In this study, the investigators will establish a cohort of highly physically active marathon runners. In a case-control design, the investigators compare muscle stem cell function across the entire spectrum of physical activity / inactivity.

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.

The investigators will also examine muscle function at the molecular level. The investigators will isolate stem cells (satellite cells) from muscles biopsy and establish primary muscle cell cultures. By electrical stimulation of these cells in vitro, the investigators can emulate a muscle contraction as during physical activity. The investigators will test the overall hypothesis that physical activity affects stem cell function.

The investigators will further study whether epigenetic phenomena (methylation) of selected DNA sequences are sensitive to training level.

Inclusion Criteria:

• 10 marathons, 2 within the last year or 50 km/week the last 5 years

Exclusion Criteria:

• smokers, any medication, chronic diseases, digestion of performance enhancing drugs, pregnancy, alcohol abuse

Runners with high amount of training