ESTIMATION OF DISC COMPRESSION DURING TRANSIENT WHOLE-BODY VIBRATION

This study was performed to examine health effects of transient whole- body vibrations on the lumbar spine. The aim was to detect extremes in the time course of compressive load acting on the disc L(3-4) in orde r to estimate the health risk which depends on the amplitude of peak v alues of compression. Five healthy males were repeatedly exposed to va rious transient displacements with nearly sinusoidal or half-sinusoida l waveforms, different durations, and peak accelerations between about 1.4 and 4.1 ms(-2). Accelerations in the z direction were measured on the skin over the spinous processes of L(3-4) in five subjects and av eraged individually. Complete time series of dynamic compressive force s were calculated by means of a biomechanical model using the calculat ed effective mass of the human body above the disc L(3-4) and relative accelerations between the vertebrae L(3-4) for the first time. The am plitudes of the absolute peak values of the compressive forces were in fluenced only by the interaction between the initial direction and the duration of the waveform. Direct comparisons with the results of othe r authors are impossible due to methodical differences and missing dat a in the time domain. The nearly constant peak compressive forces with a shorter du ration of transients connected with a higher-frequency c ontent support the proposal to put more weight on vibrations above 8 H z in a revised International Standard ISO 2631. The comparison of the calculated internal forces with results of in-vitro studies indicates a possible health risk for persons with a low vertebral strength durin g repetitive exposures to moderate transient whole-body vibrations. Re levance The mechanical strain of the lumbar spine caused by transient whole-body vibration is examined, The consideration of the health risk caused by similar exposures can contribute to a better prevention of work-related low back pain.