Oxygen is required for an optimal muscle function. In patients with diabetes mellitus, hyperglycemia can cause vascular complications. The endothelium (inter layer of the blood vessels) can be damaged leading to a reduced oxygen flow towards the muscle cells. Besides, it is possible that mitochondrial dysfunction is occuring leading to reduced extraction of oxygen. Both conditions will lead to a reduced flow of oxygen towards the muscle and this can have impact on the production of energy necessary for optimal functioning. In this study, the investigators will examine the functionality of the blood vessels (1) and the uptake of oxygen into the muscles (2) in patients with diabetes mellitus type 1 and type 2 (with and without vascular complications) compared to healthy persons.