The recent application of strained silicon into transistor design has led to significant progress in increasing the performance of devices. However, up to now little is known about the mechanical behaviour of the strained Si layers and the elastic properties of the deformed semiconductor lattice. The perturbed angular correlation method is ideally suited to study strain related local phenomena in silicon using the acceptor 111In as probe. In the past, the influence of external uniaxial strain on In acceptors in pure Si and on donor-acceptor pairs in silicon has been investigated intensively (G. Marx, R. Vianden, Phys. Lett. A210, 364 1996; G. Tessema, PhD thesis, University of Bonn, 2003). In the course of these studies it was found that the unpaired indium probes on regular lattice sites showed an unexpected reaction to uniaxial strain, which depended on the dopant species. Our current experiments reveal that the tension induced local deformation around the In probe atoms also depends on the concentration of the co-implanted donors suggesting a local change of the elastic properties of silicon. In addition, the reaction of the silicon lattice to tensile strain applied along different crystal axes showed strong differences.