Optimal Verbal Instruction to Improve Walking for PD

Each participant will receive 12 treatment with special verbal instruction which depends on participant's group. Each training session will last 60 minutes, including 5 minutes of warm-up stretching exercise, 40 minutes of treadmill training, and 15 minutes of over-ground gait and balance training. Throughout the 40 minutes of treadmill walking, the participants will walk on the level of 0% slope with a body-weight support system (LikorallTM 200, Liko, Sweden) used to protect the participants from falling; no actual weight support of the body will be provided. The frequency of intervention will be 2-3 days a week, spread across 4-6 weeks. The intervention protocols will be the same for all groups except the instruction provided to the participants in each group.