Mechanical relaxations of strained silicon on insulator (sSOI) nanostructures are studied for the isolation and implantation processes used in transistor technology. Two model systems are quantitatively analyzed by grazing incidence x-ray diffraction: long etched sSOI lines of different widths and bidimensional (2D) sSi samples implanted by As/Xe ions with the same stripe geometry, the gate stack acting as an implantation mask. For sSOI lines, the strain of the initial 2D layer is conserved along the longer direction, i.e., the transport direction. Along the small direction, a large relaxation is observed especially for the smaller widths. This relaxation is almost complete for thicker samples (70 nm), whereas it is much more limited for thinner ones (10 nm). The tuning by etching/size selection of the sSOI initial biaxial stress into uniaxial stress along the transport direction should represent a great advantage for n-metal oxide semiconductor (n-MOS) devices in terms of mobility. Similar relaxation anisotropies have been observed for the implanted samples with 60 nm thickness. In this case, the relaxed small dimension of the area under the gate stack corresponds to the transport direction. This direct source/drain implantation step should therefore damage the performance of partially depleted sSOI n-MOS devices. However these relaxation phenomena should be advantageously used with new integration schemes.