DIFFERENTIAL SHOCK TRANSMISSION RESPONSE OF THE HUMAN-BODY TO IMPACT SEVERITY AND LOWER-LIMB POSTURE

The shocks imparted to the foot during locomotion may lead to joint-de generative diseases and jeopardize the visual-vestibular functions. Th e body relies upon several mechanisms and structures that have unique viscoelastic properties for shock attenuation. The purpose of the pres ent study was to determine whether impact severity and initial knee an gle (IKA) could alter the shock transmission characteristics of the bo dy. Impacts were administered to the right foot of 38 subjects with a human pendulum device. Combinations of velocities (0.9, 1.05 and 1.2 m s(-1))and surfaces (soft and hard foams) served to manipulate impact severity in the first experiment. Three IKA (0, 20 and 40 degrees) wer e examined in the second experiment. Transmission between shank and he ad was characterized by measuring the shock at these sites with miniat ure accelerometers. Velocity and surface had no effect on the frequenc y profile of shock transmission suggesting a consistent response of th e body to impact severity. Shank shock power spectrum Features account ed for the lower shock ratio (head/shank) measured under the hard surf ace condition. IKA flexion caused considerable reduction in effective axial stiffness of the body (EASE), 28.7-7.9 kN m(-1), which improved shock attenuation. The high correlation (r = 0.97) between EASE and sh ock ratio underscored the importance of EASE to shock attenuation. The present findings provide valuable information for the development of strategies aimed at protecting the joints, articular cartilage, spine and head against locomotor shock. Copyright (C) 1996 Elsevier Science Ltd.