The goal of this clinical trial is to study the effects of aerobic exercise during the early rehabilitation after ischemic stroke. The main questions it aims to answer are:

• How is the recovery of motor function affected by regularly walking during the first 90 days after an ischemic stroke?
• Does regularly walking during the first 90 days after ischemic stroke affect cognition, physical comfort and the immune system? Participants will exert a heart rate controlled walking programme of walking 3-5 times 30-45 minutes per week. Researchers will compare the recovery of the walking group to a control group without any demands regarding physical exercise.

From animal experiments we know that wheel running has a positive impact on functional recovery after experimental stroke. We aim to translate this observations from our animal experiments into the clinic. Therefore, patients will be included shortly after ischemic stroke and start an aerobic exercise programme during the first 14 days after the event. At baseline visit the participants receive a neuropsychological testing with the focus on cognition, fatigue and depressive symptoms. Furthermore, we perform blood sampling for analysis of the activation state of the peripheral immune system. The patients receive a lactate ergometry with measurement of the 3 mmol lactate threshold to define the optimal heart rate range for their walking exercise. We perform the fugl-meyer assessment for the upper and the lower extremity.

For correlation with training-induced structural changes participants receive cerebral magnetic resonance imaging to assess the density of axonal fibre tracts (assessed by MRI-DTI). During the following 90 days participants in the intervention group are instructed to walk 3-5 times for 30-45 minutes per week and control the exercise intensity by optical heart rate measurement via smartwatch. The daily step count will be protocolled by the intervention and the control group. Participants will measure their resting heart rate in the morning before getting up to prevent overexercising. The assessments of the baseline visit will be repeated after 90 days.

Inclusion Criteria:

• initial NIHSS or NIHSS determined at the moment of maximum deterioration 1-18
• age > 18
• ischemic stroke
• pre-stroke independence
• sufficient motivation / patient's desire to cooperate / exercise for 3-5x/week for 30-45 min

Exclusion Criteria:

• transient ischemic attack
• premorbid motor disability / musculoskeletal injury / severe arthritis impairing degree of movement
• balance and transfer function that requires assistance
• cardiac disease not allowing to perform aerobic training
• inability to give informed consent