  Lipid bilayer membranes are commonly modeled as area-preserving fluid
surfaces that resist bending. There appear to be two schools of thought in the
literature concerning the actual area constraint. In some works the total or
global area (GA) of the vesicle is a prescribed constant, while in others the
local area ratio is assigned to unity. In this work we demonstrate the
equivalence of these ostensibly distinct approaches in the specific case when
the equilibrium configuration is a smooth, closed surface of genus zero. We
accomplish this in the context of the Euler-Lagrange equilibrium equations,
constraint equations and the second-variation with admissibility conditions,
for a broad class of models - including the phase-field type.
