Fig. 1
Postural control model, an inverted pendulum as ‘Body’ with PID controller representing the CNS, and time delay. The human ‘Body’ is modeled by an inverted pendulum with all mass (mB) centered at the height of h. J = moment of inertia of body around ankle axis; mf = 2.01 kg, mass of feet; hf = 0.085 m, height of the ankle axis above the ground; df = 0.052 m, the horizontal distance between the ankle axis and the center-of-mass of the feet [9]; θ, body sway angle, yp, center-of-pressure (COP) displacement. The neuromuscular controller is modeled by PID controller: KP (proportional gain) main control parameter for generating corrective ankle torque; KD (derivative gain), KI (integral gain) control parameter responsible for undesired steady lean from upright stance. Ta, corrective ankle torque; Td, disturbance torque; Kn, internal disturbance torque gain; τf = 100 s, time constant for low-pass filter; τd, time delay