Outpatient Physical Therapy Intervention in Subjects With Parkinson's Disease Currently Using APOKYN®

Inclusion Criteria: * Able to understand and sign an Investigational Review Board (IRB)-approved written informed consent and privacy language (e.g., Health Insurance Portability and Accountability Act (HIPAA) authorization) as per national regulations before any study-related procedures are performed. * Must have a diagnosis of idiopathic PD. * Adult male or female 18 to 78 years of age, inclusive. * Currently using APOKYN, per the Package Insert, for at least 4 weeks before Baseline Assessment Visit(s). * Currently using carbidopa/levodopa therapy at a steady maintenance dose, representing a stable treatment regimen in the opinion of the Investigator, for at least 4 weeks before Baseline Assessment Visit(s). * Able to walk 50 feet independently (cane permissible) at the Baseline Assessment Visit. * Meet all of the following parameters to demonstrate an optimal response to APOKYN at the APOKYN Response Verification Visit: must be "on" in the opinion of the subject and investigator within 20 minutes after the APOKYN injection; and have a motor state improvement of \>25% per the Movement Disorder Society (MDS)-UPDRS Motor Score (Part III), within 20 minutes after the APOKYN injection, as compared to pre-injection. * Willing and able to comply with scheduled visits, treatment plan, other study-related procedures, and have available caregiver to provide transportation to clinic visits as needed. Exclusion Criteria: * Received PT targeting Parkinson's disease within 6 months before Baseline Assessment Visit(s). * Received any investigational (i.e., unapproved) drug product within the last 30 days (or 5 half-lives, whichever is longer) before the Baseline Assessment Visit(s). * Currently taking, or likely to need to take at any time during the course of the study, any 5HT3 antagonist (i.e., ondansetron, granisetron, dolasetron, palonosetron, alosetron). * Currently on or likely to transition to the DUOPA (carbidopa and levodopa enteral suspension) during the course of the study. * Has orthostatic hypotension (defined as \>30 mmHg decrease in systolic blood pressure or \>15 mmHg decrease in diastolic blood pressure within 2 minutes of standing from a supine position) at the Baseline Assessment Visit(s), or within 20 minutes following APOKYN injection at the APOKYN Verification Visit. * Has a score of 24 or higher on the Modified Physical Performance Test (M-PPT). * Has a score of 80% or higher on the Activities-specific Balance Confidence Scale (ABC). * Has any significant current medical disorder, physical, or mental condition that would, in the Investigator's opinion, represent a hazard to the subject or prevent the subject from completing the study. * Subjects with dementia, in the Investigator's opinion, or subjects with a Montreal Cognitive Assessment (MoCA) \<18.