Fig. 3
The patient-specific postural control model of PD. The model consisted of human ‘Body’, CNS in form of a PID controller, and time delay (τd). The ‘Body’ was modeled by an inverted pendulum with all mass (mB) centered at the height of h (which were adjusted patient-specifically). J, moment of inertia of body around ankle axis. The COP displacement (yp) was calculated from the body sway angle (θ) considering the feet mass (mf = 2.01 kg), which is fully described in [37]. The CNS was modeled by a PID controller: KP (proportional gain—quantifies the stability degree), KD (derivative gain), KI (integral gain). Ta, corrective ankle torque; Td, disturbance torque; Kn, internal disturbance torque gain which quantifies the flexibility degree; τf = 100 s, time constant for low-pass filter