Table 1.

List of symbols

Symbol	Meaning
F Cx	Sum of the horizontal ground reaction forces
F Cy	Sum of the vertical ground reaction forces
g	Gravitational acceleration
h A	Ankle height w.r.t. the ground
K	Proportional gain of the virtual-ankle stiffness controller
K D	Derivative gain of the body sway controller
K P	Proportional gain of the body sway controller
l com	Height of the center of mass in upright stance w.r.t. the ankle
M	Subject mass
p x	Center of pressure in anteroposterior direction w.r.t. the ankle
θ sway	Body sway angle
τ ach	Desired support torque
τ tot	Total torque applied to the ankle
ϕ A	Ankle joint angle