Knowledge of the mass and inertial parameters of a humanoid robot or a human being is crucial for the development of model-based control as well as for monitoring the rehabilitation process. These parameters are also important for obtaining realistic simulations in the field of motion planning and human motor control. For robots they are often provided by CAD data while averaged anthropometric tables values are often used for human subjects. The unit/subject specific inertial parameters can be identified using the external wrench caused the ground reaction. However, the identification accuracy intrinsically de- pends on the excitation properties of the recorded motion. In this paper, a new method for obtaining optimal excitation motions is proposed. This method is based on the identification model of legged systems and on optimization processes to generate excitation motions while handling mechanical constraints. A pragmatic decomposition of this problem, the use of a new excitation criterion and a quadratic program to identify inertial parameters are proposed. The method has been experimentally validated onto a HOAP-3 humanoid robot and with one human subject.