Participants in the Intervention group exercise three times a week for 30 minutes on a bicycle ergometer (optibike med, ergoline GmbH, Bitz, Germany) in the integrated gym hall of one of the participating residencies. Training is individualised as respective performance is adapted to the power at the first ventilator threshold (assessed during cardiopulmonary exercise test).

Participants of Waiting Control continue their regular physical activity behaviour for 12 weeks. They will start the same exercise intervention after a reassessment at week 12 for the next upcoming 12 weeks. (13-24)

During the first 4 weeks of intervention two of the three weekly training sessions are offered as group training supervised by the respective qualified exercise physiologist of the Department of Sports Medicine. After 4 weeks, participants' physical performance is reassessed at the Department of Sports Medicine. If necessary, workload is readjusted to achieve the initially defined exercise intensity.

assessed by MRSI, Primary hypothesis is that aerobic exercise leads to an increase of cerebral N-acetyl-aspartate (NAA; mediated by plasma neurotrophins).

Secondary hypothesis stipulates an increase of markers of neuronal energy reserve: i.e. the ratio of phosphocreatinin to creatinine and of adenosine-tri-phosphate (ATP) to ~di-phosphate (ADP).

Third hypothesis is an increase in the volume of cortical grey matter

Aerobic exercise capacity is determined by a physician-supervised CPET