  Parkinson's disease (PD) is a neurodegenerative disorder characterized by
increased response times leading to a variety of biomechanical symptoms such as
tremors, stooping and gait instability. Although the deterioration in
biomechanical control can intuitively be related to sluggish response times,
how the delay leads to such biomechanical symptoms as tremor is not yet
understood. Only recently has it been explained from the perspective of
feedback control theory that delay beyond a threshold can be the cause of
Parkinsonian tremor [1]. This paper correlates several observations from this
perspective to clinical facts and reinforces them with simple numerical and
experimental examples. This work provides a framework towards developing a
deeper conceptual understanding of the mechanism behind PD symptoms.
Furthermore, it lays a foundation for developing tools for diagnosis and
progress tracking of the disease by identifying some key trends.
