CDF	cumulative distribution function
CoM	center of mass
CoP	plantar center of pressure
D	distal
DoF	degree of freedom
DS	double-support phase of the walking gait
e	mean efficiency
$F_{P1P2, P3}$ $M_{P1P2, P3}$	force (f) or moment (m) at P1: r: robot; h: human P2: a: ankle, k: knee; h: hip P3: x: anterior–posterior; y: medial–lateral or z: vertical (superior–inferior)
g	gravitational constant
GRF	ground reaction forces
HAT	head–arms–trunk
HRI	human–robot interaction
I	rotational inertia
ID	inverse dynamics
LS	link segment
m	mass
P	proximal
S	human subject
SS	single-support phase of the walking gait
$v_w$	walking speed
w	walking