α	Muscle pennation angle
Ĵ	Augmented cost function
λ	Lagrange multiplier in optimization
A	Data matrix
C	Coefficient matrix
S	Synergy matrix
θ	Angle in the operational space
a	Muscle activation
a*	Optimal muscle activation level
F	Muscle force
fl	Muscle force-length relation
fv	Muscle force-velocity relation
F0max	Maximum isometric muscle force
h	Non-linear transformation from muscle activity to operational space torque
J	Cost function in optimization
K{p, i, d}	PID parameters
l	Number of samples in the NNMF data matrix
m	Number of muscles in the models
n	Number of synergies in NNMF algorithm
r	Muscle moment arm
S	Synergy ratio
s	Slack variable in optimization
T	Torque in the operational space
w	Weighting factor in objective function