[en] The paper considers the optimization of the flexible components of mechanical systems modeled as multibody systems. This approach aims at considering as precisely as possible the dynamic loading of the structural components under service conditions in their mechanical systems. While most of the structural optimization developments have been conducted under static or quasi static conditions, the approach is clearly a challenge. Naïve applications of this approach generally lead to fragile and unstable results. To elaborate a robust and reliable approach, we investigate and compare several formulations of the optimization problem. Different optimization algorithms are also tested. To explain the efficiency of the various solution approaches, the complex nature of the design space is investigated. The developments are illustrated using the test-case of the structural design of the links of a two-arm robot subject to a trajectory tracking constraint.