Brief Title: Aerobic Training on Cerebrovascular Function, Cognition and Gait in Parkinson's Disease

This is a parallel-group randomized controlled trial Participants (n=40) diagnosed with Parkinson's disease, stages 1-3 on Hoehn \& Yahr scale, will be randomly allocated (1:1 block randomization) to: * Aerobic Training Group; * Control Group (usual care) The intervention will last 12 weeks, 3 sessions/week Pre and post-intervention assessments will include: * Cerebrovascular function: neurovascular coupling, cerebrovascular reactivity (breath-holding index), dynamic cerebral autoregulation (transfer function analysis), and acute cerebral blood flow response to exercise (transcranial Doppler; vertebral artery flow during silent reading). * Peripheral vascular and cardiovascular function: brachial artery flow-mediated dilation, carotid intima-media thickness, resting blood pressure, resting heart rate, cardiorespiratory fitness (VO₂peak), heart rate variability (time and frequency domains), and baroreflex sensitivity. * Cognitive performance: Montreal Cognitive Assessment (MoCA), Trail Making Test A and B, and Stroop Color-Word Test. * Gait biomechanics: spatiotemporal parameters, 3D kinematics (Vicon system), and kinetics (force platform). * Clinical and non-motor symptoms: UPDRS, Non-Motor Symptoms Scale (NMSS), sleep quality (PDSS), anxiety (PAS), depressive symptoms (GDS-15), apathy (Apathy Inventory), fatigue (Parkinson Fatigue Scale), pain (Numeric Rating Scale), and quality of life (PDQ-8). * Body composition: quadriceps muscle thickness and subcutaneous adipose tissue thickness assessed by ultrasound. All experimental sessions will be performed in the "on" medication state