In simulation of biomechanical structures the patient-specific geometry of the object of interest is very often reconstructed from in vivo medical imaging such as CT scans. Such geometries therefore represent a deformed configuration stressed by typical in vivo conditions. Commonly, such structures are considered stress free in simulation. In this contribution we present and compare two methods to introduce a physically meaningful stress/strain state to the obtained geometry for simulations in the finite strain regime and demonstrate the necessity of such prestressing techniques. One method is based on an inverse design analysis to calculate a stress-free reference configuration. The other method developed here is based on a modified updated Lagrangian formulation. The formulation of both methods is provided in detail and implementation issues are discussed. Applicability and accurateness of both approaches are compared and evaluated utilizing an analytical aorta model and fully three-dimensional patient-specific abdominal aortic aneurysm structures in the finite strain regime.