Optimal Verbal Instruction to Improve Walking for PD

Background: One of the most disturbing motor symptoms in Parkinson's disease (PD) is gait disturbance. Clinicians often use various verbal instructions to correct abnormal gait patterns, and the most commonly used instruction is 'lift the foot up and make big steps.' Despite immediate performance improvement, people with PD are reluctant to walk outdoors with this exaggerated walking strategy because it makes them feel embarrassed, unbalanced, and fatigue easily. Since people with PD walk with flat foot, the investigators propose that an instruction emphasizing heel-strike at foot contact may be effective. When delivering verbal instructions, clinicians should also consider the attentional focus of the instruction. Evidence has shown that instructions with external focus of attention (EF) is more beneficial than internal focus of attention (IF) for motor performance and learning. However, most of the gait-related instructions for PD are IF. The investigators thus aim to design a novel EF instruction and determine whether people with PD can benefit more from EF than IF instruction. Objectives: (1) To investigate the effects of verbal instruction emphasizing heel-strike during gait training in people with PD. (2) To further determine whether an instruction with EF will induce greater training benefits than IF. Methods: Two experiments will be conducted in this study. In experiment 1, 60 individuals with PD will be randomized into the heel-strike (HS), big-step (BIG), and control (CON) groups. All participants will receive 12 sessions of gait training with the specific verbal instruction allocated for each group. The participants will be assessed before, immediately after, and 4 weeks after the interventions. The primary outcome will be gait performance, and the secondary outcomes will include measurements of cognitive and behavioral functions. Additionally, transcranial magnetic stimulation will be used to examine the changes of corticomotor excitability associated