**5.1 Introduction to LifeMOD simulation software**

Recently, many software applications have been developed for impact simulation, ergonomics, comfort study, biomechanical analysis and surgical planning. Such software enables users to perform human body modeling and interaction with the environment where the human motion and muscle forces can be simulated. These tools are very useful for simulating the human-machine behavior simultaneously. LifeMOD from Biomechanics Research Group is a leading simulation tool that has been designed for this purpose.

The LifeMOD Biomechanics Modeler is a plug-in module to the ADAMS (Automatic Dynamic Analysis of Mechanical Systems) physics engine, produced by MSC Software Corporation to perform multi-body analysis. It provides a default multi-body model of the skeletal system that can be modified by changing anthropometric sizes such as gender, age, height, weight etc. The created human body may be combined with any type of physical environment or system for full dynamic interaction. The results of the simulation are the human motion, internal forces exerted by soft tissues (muscles, ligaments, joints) and contact forces at the desired location of the human body. Full information on the LifeMOD Biomechanics Modeler can be found online (LifeMOD).

In following subsections, the developing process of a detailed musculo-skeletal spine model is presented thoroughly. This process includes five main stages such as generating a default human body model, discretizing the default spine segments, implementing ligamentous soft tissues, implementing lumbar back muscles and adding intra-abdominal pressure.
