Two-legged stance. The distribution of principal stresses as the tension in the spring elements is increased. The length and direction of the arrows show the relative magnitude and direction of compression, in blue, and tension, in red. (a) Without spring elements, showing generation of tension in the group 1 trabeculae. Increasing the initial strain to (b) 2.5%, (c) 5% and (d) 10% shows how the stresses become compressive throughout the proximal femur and focussed into the arch of the group 1 trabeculae.