It is well known that continuous physical exercise leads to a number of changes in the body. Maximal oxygen uptake; the heart's pumping ability and muscle mass and strength increases. Also the metabolism adapts: The ability to oxidize fat increase and the insulin sensitivity in primarily in muscle, but also in the liver increase.

Also endocrine glands adapts according to the level of physical activity. It is known that in healthy, younger people the insulin secretion from the pancreas after administration of sugar consumed orally or given directly into a vein, is significantly lower in trained individuals compared with untrained. This change does, however, not only apply to glucose, as also stimulation by the amino acid arginine, shows the same pattern.

It seems plausible that the endocrine glands/cells adapts to the level of physical training, but this has not yet been investigated.

The gastrointestinal tract is the birthplace of a variety of hormones. One group of these is called incretin hormones. They stimulate the glucose dependant insulin secretion in the pancreas and affect hunger/satiety. Whether the incretin production and thus their concentration in the blood is regulated by physical training is unknown.

Obese and patients with type 2 diabetes, has, in contrast to well-trained, decreased insulin sensitivity. As a consequence their (type 2 diabetics, at least early in their disease course) meal stimulated insulin release is greater than in healthy, normal weight individuals. This in spite of the fact that the incretin effect is reduced in obese people and patients with type 2 diabetes compared to healthy, normal weight.

Whether physical training affects both the secretion of incretins and the incretin effect has not yet been studied.

The purpose of this study is to investigate whether incretin hormones in physical well-trained young men have a changed effect on insulin secretion from the pancreas compared to untrained young men. A difference may indicate that the body's endocrine glands adapts to training mode.

The investigators hypothesis is that incretin hormones have a decreased effect on the glucose dependant insulin release in physically trained persons and thus results in a lower insulin release at any given plasma glucose level.

Inclusion Criteria:

• Sedentary: 50>Maximal oxygen uptake (VO2max), ml*min-1*kg-1 OR endurance trained VO2max, ml*min-1*kg-1>60
• 20-30 years
• BMI: 18,5-25kg/m2
• Caucasian
• Healthy

Exclusion Criteria:

• Any kind of medication or diabetes in the family (parents, siblings),
• Non-caucasian

Danish University Students from University of Copenhagen,