Effects of Transcranial Direct Current Stimulation Combined With Nordic Walking on Gait and Balance in Parkinson's Disease

Inclusion Criteria: * Idiopathic Parkinson's disease (e.g., UK Brain Bank criteria) * Hoehn \& Yahr stage II-IV (on medication) * Stable antiparkinsonian medication for ≥4 weeks before enrollment * Slowed gait phenotype (e.g., ≥6 seconds on 10-Meter Walk at preferred speed) * Able to ambulate at least 10 meters with or without a cane/poles (no hands-on assistance from a therapist) * Able to follow simple commands; provides written informed consent (MMSE ≥24 or equivalent cognitive screening) * Willing to maintain stable PD medication and usual care during the 4-week intervention, unless medically required Exclusion Criteria: * Contraindications to tDCS: implanted cranial/brain devices (e.g., DBS), metal in the skull (excluding dental), active skin disease/lesions at electrode sites, uncontrolled epilepsy or history of seizure in the past 12 months * Unstable medical or psychiatric conditions that preclude safe participation (e.g., uncontrolled hypertension, recent cardiovascular events, severe orthostatic hypotension with syncope) * Severe freezing of gait or fall risk that prevents safe participation in supervised Nordic Walking, as judged by the clinical team * Severe musculoskeletal or vestibular disorders that limit walking with poles; severe uncorrected visual impairment * Cognitive impairment incompatible with consent or testing (e.g., MMSE \<24) * Current participation in other interventional trials targeting gait/balance or brain stimulation; recent initiation or dose change of antiparkinsonian medication within 4 weeks.