They showed that active robotic assistance resulted in significantly greater gains in motor function than in individuals who received passive robotic assistance.

Active Passive Assisted Active
Motor Function * * *
Balance *
Posture & GAIT * *
Bradykinesia *
Cardiovascular Fitness * *
Tremors *
Forced, Not Voluntary, Exercise Improves Motor Function in Parkinson’s Disease Patients.

https://www.ncbi.nlm.nih.gov/pubmed/19131578

Dynamic high-cadence cycling improves motor symptoms in Parkinson’s disease.

These findings show that dynamic cycling can improve PD motor function and that activation of proprioceptors with a high cadence but variable pattern may be important for motor improvements in PD.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4557094