THE IMPACT RESPONSE OF THE SEATED SUBJECT

An impact method for establishing the dynamic response of the seated subject is introduced. The method employs a pendulum to apply the impact to the suspended seat. Pins are placed in the spinous process at L3. Highly reproducible results are obtained. The results were not affected by the amplitude of impact, implying a linear system. A marked peak of transmissibility is found in the 4-5 Hz range and an attenuation peak is found close to 8 Hz. Both muscle contraction and postural changes affect the dynamic response. A relaxed posture shows greater gain and attenuation peaks. A valsalva stiffens the system and reduces the effective damping. The vertical response of the body probably shows in the 5-6 Hz peak, while the rotational response is probably encompassed in the 8 Hz attenuation peak.