Male volunteers restrained by a lap-shoulder belt system were subjected to static and dynamic (low level impact acceleration) tests in a simulated automobile environment while electromyographic (EMG) activity of various lower extremity muscles was recorded. 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 tests were made with an embalmed cadaver and a dummy. While reflex responses of the relaxed volunteer were found too slow to affect loads and accelerations sustained, the voluntary pre-impact contracted musculature in a subject was found to reduce certain acceleration levels and to change the restraint load distribution. Significantly more load went through the legs to the floor board, with a concomitant lowering of seat and belt loads. Although a similar load distribution was seen in cadaver and dummy tests, the response of the relaxed or tensed volunteer was substantially different from either surrogate.
Abstract