Schematic representation of sensorized surface related constraints. The figure shows the location of load cells on the right sensorized surface. The three-axial load cells (1, 2) are fixed to the ground (cylindrical rails) and each of the mono axial cells (3, 4) is connected to the frame by a two degrees of freedom free rail system. All tips of the load cells are connected to the sensorized surface by spherical joints. Areas A represent the rectangular extent where the load was applied during the FEA. In particular, A represents the area used by a subject while walking across both treadmills.