<qa>  How many people without disability will be recruited in the first year?In the first year, 20 people without disability will be recruited. The APA before voluntary COP displacement test, APA before GI, and gait performance will be evaluated. In the second year, 15 people with PD and 15 healthy people will be recruited. Subjects will receive GI test, gait test, and APA before voluntary COP displacement test. The relationship between different types of APA will be established for PD and healthy people. In the third year, 30 people with PD will be randomized into APA training group, balance group, and control group. The different training effect will be evaluated especially on GI, gait performance, and freezing of gait. 