The huge amount of people who suffer from some form of disability implies that more research has to be done in order to develop efficient robotic technologies for them. Yet, research costs can not be neglected. In this matter, software simulators play a significant role as an alternative approach to minimize such expenses. This project aims to make use of OpenSim API and Simbody API, two C++ libraries in order to prove the feasibility of coupling and simulating an exoskeleton model with a musculoskeletal model. Due to the few information related about how to get it, this thesis embraces many others sub-goals strictly related to the achievement of the primary purpose. The first sub-objective has been to learn OpenSim and Simbody API. As solution proposed in this project has been to create a double pendulum model in OpenSim. The second one has been design a model of an exoskeleton. As a result, it has been implemented in OpenSim, and a controller has been designed to test it. The successful achievement of the previous sub-objectives have allowed to create the simulation of the exoskeleton coupled to the musculoskeletal model and simulate it in OpenSim. Last but not least, the documentation throughout the project in conjunction with the successful achievement of the proposed goals has made possible the creation of this thesis which indeed aims to keep working with the exoskeleton coupled to musculoskeletal model or even become a reference in future robotic orthosis projects build in OpenSim and Simbody APIs.