Lumbar vertebra mechanics in virgin, lactation, and 6-week post-weaning rats. (a)–(c) Extrinsic properties of the vertebra measured through compression testing of L2: (a) peak load, (b) stiffness, (c) energy to failure. (d)–(f) Apparent-level properties derived through normalization of L2 compression results for bone size: (d) ultimate stress, (e) elastic modulus, (f) toughness. (g)–(h) Nanoindentation of L1: (g) schematic illustrating the locations where nanoindentation was performed to assess material properties of the surface and center regions of the trabeculae, (h) nanoindentation-based Young’s modulus at the center and surface regions. * indicate significant differences among groups (p < 0.05).