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Due to the sparsity of cadaver lumbar shear stiffness data, tests on functional lumbar spinal units and a complete lumbar section (T12-L5) were done in both the anterior and posterior directions. Similar tests were performed on the Hybrid III lumbar spine for comparison. Sixteen lumber motion segments were tested quasi-statically for their viscoelastic properties in a multi-directional (5-axis) spine machine. A hydraulic testing machine was used to carry out dynamic tests including cyclic tests at several rates of deformation (0.5 - 50 mm/sec) and relaxation tests (300 sec) to determine the associated viscoelastic properties in constrained and unconstrained modes. The specimens were then loaded to sufficient displacement to cause hard or soft tissue failures. In the quasi-static tests the shear response was linear and the anterior stiffness (155 ± 90 N/mm) was found to be higher than posterior stiffness (104 ± 38 N/mm).