Biodynamic Response of the Musculoskeletal System to Impact Acceleration

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 −G_x 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.

It was found that reflex responses of the relaxed volunteer are too slow to have a significant effect on loads and accelerations sustained. However, the voluntary pre-impact contracted musculature in a volunteer can reduce certain acceleration levels and change the restraint load distribution so that significantly more load goes through the legs to the floor board with a concomitant lowering of seat and belt loads. Although a similar load distribution was seen in dummy and cadaver tests, the response of the relaxed or tensed volunteer was substantially different from either surrogate.