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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).

The effect of muscular response on occupant dynamics was studied in human volunteers exposed to low level impact acceleration. The study includes identification of muscular response, correlation of electromyographic activity with reaction force, and investigation of the effects of muscular restraint during impact. Human volunteers were subjected to −Gx impact acceleration in a simulated automobile environment while EMG activity of various lower extremity muscles was monitored. The seat and floor pan were supported on load cells which measured all restraining forces. Nine–accelerometer modules and high-speed photography were used to measure kinematics. Identical runs were made with an embalmed cadaver and dummy for comparison. Static EMG and force traces as well as dynamic results for various acceleration levels are presented. Differences between tensed and relaxed states are compared and discussed as to EMG response, force levels, and head kinematics.

The biodynamic response of cadaver torsos subjected to -Gx impact acceleration is discussed in this paper, with particular emphasis on the response of the vertebral column. The existence of an axial force along the spine and its manifestation as a load on the seat pan are reported. Spinal curvature appears to be an important factor in the generation of this spine load. In anthropometric dummies, the spine load does not exist. Details of the testing and results are given, and the development of a mathematical model is shown.