The adverse effects of car seats and vibration frequencies on different lumbar intervertebral discs in different age groups.

The prolonged whole-body vibration (WBV) may be one of the important factors contributing to low back pain. This study used a validated whole-body model and the WBV evaluation standard (ISO 2631-5:2018) to investigate the effects of car seat, frequency and age on the risk factors of the lumbar spine during prolonged exposure to WBV. The modal frequencies contributing more to the human resonance were first preliminarily predicted by modal analysis, and then sinusoidal excitations with frequencies of 1, 3, 5, 7, 9, 11 and 13 Hz were applied for transient analysis. On this basis, the adverse effects of long-term WBV on the lumbar spine were assessed based on the risk factors defined in the WBV evaluation standard (ISO 2631-5:2018). The transient analysis and risk factor calculation demonstrated that the responses exhibited a pronounced frequency dependence, with the highest response occurring at 4 Hz and 5 Hz excitation for elastic and rigid car seats, respectively. Rigid car seat increased disc von Mises stress and risk factors by 7.6% and 11%, respectively, compared with elastic one. After 5 years from the age of 25, the peak risk factors for human-body exposure to vibration were 0.73 and 0.81 for elastic and rigid car seats, respectively and continued to increase with age. From age 45 onwards, the adverse effects of vibration on the lumbar spine will reach a risk level considered dangerous after 5 years.