This paper proposes an analysis of the effect of vertical position of the pivot point of the inverted pendulum during humanoid walking. We introduce a new feature of the inverted pendulum by taking a pivot point under the ground level allowing a natural trajectory for the center of pressure (CoP), like in human walking. The influence of the vertical position of the pivot point on energy consumption is analysed here. The evaluation of the energy consumption is done using a sthenic criterion in a 3D dynamics simulation of the humanoid robot ROMEO (Aldebaran Robotics) and shows a consequent reduction of the robot torque solicitation with a pivot point under the ground.